volcano scientist

Etna Week (Part 3) - Etna's Volcanic Hazards

eklemetti — Fri, 20 Aug 2010 02:05:36 +0000

Etna Week (Part 3) - Etna's Volcanic Hazards

The final part of Etna Week, brought to us by guest blogger Dr. Boris Behncke. Check out Part 1 and Part 2 as well!

Etna Volcanic hazards
By guest blogger Dr. Boris Behncke.

Etna is one of the most active volcanoes on Earth, and a population of nearly one million people dwell on its flanks, many in areas that have been repeatedly invaded by lava flows during the historical period. A few villages have been constructed very close to the vents of eruptions only a few hundred years old.

Top: Residential areas surrounding numerous pyroclastic cones on the lower southeast flank of Etna, seen from Monte Arso, a cone that erupted in the late Middle Ages looking toward the metropolitan areas of Acireale and Catania. The cones seen in this image are all prehistoric but just outside the field of view are a few cones that erupted during the past 2000 years. Photo taken in 2000 by Boris Behncke. Bottom: A volcanologist's dream and nightmare - one day, a new crater will open and grow into a new cone in our backyard, like shown in this apocalyptic photomontage (the big cone formed during the 2001 south flank eruption projected onto a photograph of my hometown Trecastagni on the southeast flank of Etna). Both original photos by Boris Behncke

As mentioned before, few people are known to have lost their lives due to eruptions of Etna. During the last century, three deadly incidents are known, in 1929 (two deaths), 1979 (nine deaths), and 1987 (two deaths); in all cases the victims were visitors to the summit crater who were surprised by sudden steam-blast (phreatic) explosions. Amazingly, many people have escaped unscathed during a number of much more violent explosive magmatic eruptions, which, however, always showed a conspicuous buildup for some time before culminating. In contrast, phreatic explosions occur virtually without warning, as has been tragically demonstrated at Galeras volcano (Colombia) in 1993, when nine people, including six volcanologists, were surprised and killed by a relatively small explosion - they happened to be near the very crater (some were even within the crater taking gas samples). [For further detail on the Galeras incident, there are two rather gripping and contrasting stories, "Surviving Galeras" written by one of the survivors, Stan Williams (in collaboration with Fen Montaigne), and "No Apparent Danger" by former-geologist-turned-into-reporter Victoria Bruce'. I recommend to read Williams first and then Bruce, after which you may be having some sort of a balanced view of things.]

Volcanic hazards at Etna are: (1) lava flows, (2) tephra falls (and volcanic ash plumes endangering air traffic), (3) earthquakes related to eruptive activity and magma movement, (4) volcanic sector collapse, (5) tsunami, (6) pyroclastic flows.

Lava flows are by far the most common hazard at Etna. About half of Etna's historically recorded eruptions have caused damage to human property due to lava flow invasion. In most cases the losses have been cultivated land, but on a number of occasions buildings have been destroyed. More rarely have population centers been impacted and partly or completely destroyed - during the past 400 years this has happened only three times, in 1651-1653, 1669, and 1928.

Etna eating towns and villages - luckily this happens quite rarely. Top image is a reproduction of a fresco exposed in the sacristy of the cathedral of Catania, which neatly shows the erupting vent (Monti Rossi) low on the south flank of Etna and the lava flow being diverted around the city of Catania by its city walls; people can furthermore be seen fleeing on boats, others holding processions, and a few housewives hanging their laundry next to the hot lava to make it dry faster.

In a recent study, Behncke et al. (2005) for the first time tried to quantify the risk posed by lava flows, diving the Etnean area into six different zones of increasing hazard, from the coastal areas to Etna's summit. This work revealed a moderately high risk of lava flow invasion in a densely populated area on the southeast flank of Etna, including Trecastagni where I and my family are living. However, such hazard zonation is of relatively limited use for land use planners and civil defense, since the boundaries of different hazard zones are relatively vague and do not reflect the morphological variations of the terrain on a scale of a few tens to a few hundreds of meters.

Mapping the lava flow hazard at Etna. Top image shows the rough subdivision by Behncke et al. (2005) into six hazard zones, bottom image renders a much refined impression of the vulnerability to lava flow invasion based on the SCIARA lava flow simulation model (Crisci et al., 2010).

A much more sophisticated effort was thus launched in recent years, which involved several groups of scientists from various universities in Italy and abroad, and the Istituto Nazionale di Geofisica e Vulcanologia. I participated in some of this work, and the results are encouraging. The main means of defining the hazard from lava flow invasion, and fine-tuning the hazard zonation and the vulnerability of the Etnean area at very high resolution, is computer simulation of lava flows. Different models have been applied at Etna for the simulation of lava flows, which are described in much detail in publications by Crisci et al. (2010), Favalli et al. (2009), and Herault et al. (2009).

It is now possible to recognize those areas that would be impacted first - obviously those lying in morphologically low areas - and where to concentrate rescue efforts and salvage operations once the location of an imminent or starting eruption is known. The tens of thousands of computer simulations carried out during the project have not only served to produce very detailed hazard maps for Etna, they also produced virtually all possible eruption (lava flow) scenarios for any location on this volcano. These scenarios can be extracted with a few mouse clicks on demand, so that simulating new scenarios causing loss of precious time will not be necessary.

The risk of damage and disruptions caused by tephra fall has been seriously underestimated at Etna until recently, mainly due to the (false) notion of Etna being a non-explosive volcano. During the about 150 episodes of lava fountaining during the 1995-2001 "Millennium Fireworks" at the summit craters, heavy showers of ash and scoria (very porous, black, centimeter-sized fragments of lava) occurred frequently on the flanks of Etna, causing damage to crops, and sometimes breaking car windshields and disrupting road traffic. During one of these episodes, on 26 April 2000, a passenger airplane starting from Catania airport with more than 100 passengers on board encountered the tephra plume and falling scoria cracked its windshield, whereupon the airplane had to return for an emergency landing in Catania. Since that incident, air traffic is severely restricted during explosive eruptions at Etna.

This became a particularly biting issue during the prolonged ash falls from the 2001 and 2002-2003 flank eruptions, and again during the 2006 summit eruption. For periods of days to weeks, the airport of Catania remained closed, sometimes even the airport of Reggio Calabria, on the Italian mainland about 70 km northeast of Etna, had to be closed as well. For this reason, people in Sicily were not particularly shocked when Iceland's EyjafjalljÃ¶kull brought all air traffic in Europe to a grinding halt in the spring of 2010 for a few days, including northern Italy.

The revelation that ash-producing flank eruptions are far more common at Etna than previously thought indicates that the population around Etna and people travelling from and to Sicily in airplanes will experience further disruptions due to ash falls about once every 10-20 years. Obviously, tephra falls will be locally devastating if a flank eruption occurs close to the populated areas, as in 1669. A similar event would bury the villages to the east and southeast - including Pedara, my home town Trecastagni, Mascalucia, Tremestieri, and a few more - under up to several meters of tephra. In this moment, I know of no preparations for such a case, and educating the public (administrators and inhabitants) to create an awareness of this and other hazards is overdue.

Earthquakes accompanying the movement of magma or caused by magma-induced flank displacement are frequent on the eastern, southeastern, and southern flanks of Etna, and often cause significant material damage and occasionally kill people. Such events cannot be predicted, and prevention such as earthquake-resistant construction is essential. Building codes are applied for new constructions since the 1980s, but an amazing quantity of residential buildings as well as hospitals and school buildings were constructed during the 1960s to 1980s without applying any codes, so that a tremendous number of such buildings are vulnerable. This is an issue of unimaginable proportions, and extends far beyond Etna's magma-related seismic activity, because all of eastern Sicily is a high-risk seismic zone due to the presence of several major regional tectonic fault systems, and a number of large population centers such as Catania and Messina lie in this area, having a building stock of which maybe 20 per cent would resist (not collapse) during a major earthquake.

Volcanic sector collapse is known to have occurred at least once during the history of Etna, about 9000 years ago, forming the Valle del Bove. This event is believed by some researchers to have caused a massive tsunami, which ravaged the coasts around the eastern Mediterranean (Pareschi et al., 2006). Although the flanks of Etna continue to be severely affected by instability, the risk of a major sector collapse and related tsunami is currently considered low.

Pyroclastic flows are a fairly new discovery at Etna, although this volcano has proved more inventive in different mechanisms to generate such flows than any other volcano. I have had the doubtful privilege to witness small pyroclastic flows in the summit area of Etna on two occasions, in 1999 and 2006, and at very close range (less than 1 km), and a few colleagues have made similar experiences. These flows were showing nearly all the characteristics of pyroclastic flows on other, generally more explosive volcanoes, but were - luckily - very small and some apparently were much cooler than their more common counterparts.

Pyroclastic flow caused by the collapse of an oblique eruption column from the Southeast Crater, on 16 April 2000. Note the numerous people near the building in the left foreground, immediately after this photo was taken they fled downslope, and no one was touched by the flow. Note the large pyroclastic fragments in the air above the pyroclastic flow. Building is Torre del Filosofo, which was buried under tephra during the flank eruption of 2002-2003. Photo courtesy of Jean-Claude Tanguy, published in Behncke (2009).

During the past 25 years, small pyroclastic flows have occurred on at least 10 occasions in the summit area and on the upper flanks of Etna. A few were caused by collapse of eruption columns, which is one of the most common mechanisms of pyroclastic flows worldwide. A fine example of this type occurred on 16 April 2000 at the Southeast Crater, when a heavily charged pyroclastic jet shot out obliquely from an opening flank vent, the heavy downpour of gas-charged fragments developing into a pyroclastic flow that passed a few hundred meters from dozens of spectators, luckily without reaching any of them. Similar events occurred in 1986 at the Northeast Crater, repeatedly during the numerous lava fountaining episodes from the Southeast Crater in 2000 (and possibly also during similar events in early 1999), and more recently, on 10 May 2008 and on 8 April 2010.

A very different scenario was the one we encountered on 25 October 1999, during the one-month-long eruption that filled the Bocca Nuova to overflowing (Behncke et al., 2003). On that day, magma pushing through hot, though largely solid material filling the crater, uplifted a portion of that material, raising it like a lava dome and thrust it over the crater rim onto the steep outer flank of the central summit cone. The flank of this dome-like mass steepened, becoming unstable and collapsing like the flanks of a growing silicic lava dome, much the same way as the lava domes of SoufriÃ¨re Hills on Montserrat or Merapi in Indonesia. The collapsing masses of hot, gas-charged rock transformed into small pyroclastic flows that traveled at a speed of about 70 km per hour, and some of us were just a few hundred meters away from these flows.

Ground and aerial views of the small pyroclastic flows that formed during the Bocca Nuova eruption on 25 October 1999. These flows were generated by the collapse of a mass of hot lava, which was pushed from inside the crater over its western rim. Note the vigorous Hawaiian-style lava fountains in both images. Photos by Marco Fulle (top) and Marco Neri (bottom)

The most impressive pyroclastic flows seen in recent years at Etna were those of November 2006, and they were also the most enigmatic in terms of the mechanisms which generated them. On 16 November, during one of many eruptive episodes at the Southeast Crater between July and December 2006, lava issuing from the summit of the cone interacted explosively with wet, hydrothermally altered rocks into which it was eroding, causing numerous small and two larger (up to 1.5 km long) pyroclastic flows (Behncke et al., 2008). Different interpretations of the causes of the larger flows were proposed by Norini et al. (2009) and Ferlito et al. (2010), the earlier proposing a purely gravitationally induced collapse of the cone (the pyroclastic flow was in fact described as a debris avalanche by Norini et al., 2009), the latter envisaging a sudden decompression of shallow magma when the cone's flank collapsed. These scenarios fail to take into account that removal of a significant portion of the cone was not an instantaneous event but occurred over more than 6 hours at a rather slow speed, a process that I and numerous colleagues had observed since early on that day. But whatever the details of the causes, the pyroclastic flows were large enough to engulf people had they travelled southward rather than southeastward. The temperature was probably low, because plastic-coated wooden signs placed along a tourist path had not suffered any heat effects, but the mechanical impact might have been deadly for any living being in the path of the pyroclastic flows.

Dramatic sequence of photos showing development of a large pyroclastic flow from the southeastern base of the Southeast Crater cone on 16 November 2006, photographed from about 1.5 km to the south. The first photo (upper left) shows the initial explosive jets that generated the flow, consisting entirely of ash, blocks, and water vapor, but little incandescent material. The abundance of water vapor indicates involvement of a large volume of wet, hydrothermal-fluid-soaked rock, which mixed and interacted explosively with hot lava flows. Building visible in the first three frames is what remains of Torre del Filosofo, largely buried under 2002-2003 tephra. Photos courtesy of M. La Rosa

Similar pyroclastic flows occurred on 24 November and were again observed at close range by a geologist (Robin Campion from Belgium), but no study of the deposits and on the triggering mechanisms was carried out in this case.

Finally, a fourth mechanism producing pyroclastic flows was discovered during an episode of lava fountaining and emission of voluminous, fast-moving lava flows from the Southeast Crater on 29 March 2007. In this case, a large lava flow encountered deep snow on a steep slope, and apparently disintegrated as snow melted and failed under the moving lava; this caused powerful explosions which in turn produced pyroclastic flows and mudflows that advanced for about 1 km downslope into uninhabited areas.

As far as can be understood from current knowledge, pyroclastic flows as those observed in the past few decades are a severe hazard for visitors to the summit area, but do not threaten the lives and property of the people living on the slopes of Etna. However, larger pyroclastic flows were generated during the cataclysmic eruptions at the end of the Ellittico stage about 15,000 years ago, and during the 122 B.C. Plinian eruption. Chances of an Ellittico-style event are extremely remote, because the magma composition is different today, but an event like in 122 B.C. cannot be fully excluded to occur even in the short term.

Much, much more could be told about Etna - such as the relationship of the volcano with the people who live next to it, and the various monitoring techniques now being applied by the Istituto Nazionale di Geofisica e Vulcanologia of Catania, as well as a number of groundbreaking research efforts. It would be well worth to indicate how Etna can be discovered by volcano and nature lovers without beating the common tourist paths. All this may come in a future guest blog - and, obviously, one day there will be a new eruption to inform you of. We are all waiting for it - hoping that we will still have a peaceful summer and maybe a peaceful Christmas, and a peaceful next year. One day time will run out, and be certain that you'll receive the news firsthand here on this blog.

References
Acocella, V., Behncke, B., Neri, M., D'Amico, S. (2003) Link between major flank slip and 2002-2003 eruption at Mt. Etna (Italy). Geophysical Research Letters, 30, 2286, doi: 10.1029/2003GL018642

Allard, P., Behncke, B., D'Amico, S., Neri, M., Gambino, S. (2006) Mount Etna 1993-2005: Anatomy of an evolving eruptive cycle. Earth Science Reviews, 78: 85-114, doi: 10.1016/j.earscirev.2006.04.002

Andronico, D., Branca, S., Calvari, S., Burton, M., Caltabiano, T., Corsaro, R.A., Del Carlo, P., GarfÃ¬, G., Lodato, L., Miraglia, L., MurÃ¨, F., Neri, M., Pecora, E., Pompilio, M., Salerno, G., Spampinato, L. (2004) A multi-disciplinary study of the 200203 Etna eruption: insights into a complex plumbing system. Bulletin of Volcanology, 67: 314-330, doi: 10.1007/s00445-004-0372-8

Armienti, P., Tonarini, S., D'Orazio, M., Innocenti, F. (2004) Genesis and evolution of Mt. Etna alkaline lavas: petrological and Sr-Nd-B isotope constraints. Periodico di Mineralogia, 73: 29-52, http://tetide.geo.uniroma1.it/riviste/permin/testi/V73/2.pdf

Behncke, B. (1998) Il vulcanesimo del Plateau Ibleo (Sicilia sud-orientale) negli ultimi 230 Ma. Bollettino dell'Accademia Gioenia Catania, 31 (N. 355): 39-50

Behncke, B. (2009) Hazards from pyroclastic density currents at Mt. Etna (Italy). Journal of Volcanology and Geothermal Research, 180: 148-160, doi: 10.1016/j.jvolgeores.2008.09.021

Behncke, B., Neri, M. (2003a) Cycles and trends in the recent eruptive behaviour of Mt. Etna (Italy). Canadian Journal of Earth Sciences, 40: 1405-1411, doi: 10.1139/E03-052.

Behncke, B., Neri, M. (2003b) The July-August 2001 eruption of Mt. Etna (Sicily). Bulletin of Volcanology, 65: 461-476, doi: 10.1007/s00445-003-0274-1

Behncke, B., Neri, M., Carniel, R. (2003) An exceptional case of endogenous lava dome growth spawning pyroclastic avalanches at Mt. Etna (Italy): the 1999 Bocca Nuova eruption. Journal of Volcanology and Geothermal Research, 124: 115-128, doi: 10.1016/S0377-0273(03)00072-6

Behncke, B., Neri, M., Nagay, A. (2005) Lava flow hazard at Mount Etna (Italy): new data from a GIS-based study. In: Manga, M., Ventura, G. (Eds), Kinematics and Dynamics of Lava Flows. Geological Society of America Special Paper, 396: 189-209, doi: 10.1130/2005.2396(13)

Behncke, B., Neri, M., Pecora, E., Zanon, V. (2006) The exceptional activity and growth of the Southeast Crater, Mount Etna (Italy), between 1996 and 2001. Bulletin of Volcanology, 69: 149-173, doi: 10.1007/s00445-006-0061-x

Behncke, B., Calvari, S., Giammanco, S., Neri, M., Pinkerton, H. (2008) Pyroclastic density currents resulting from the interaction of basaltic magma with hydrothermally altered rock: an example from the 2006 summit eruptions of Mount Etna, Italy. Bulletin of Volcanology, 70: 1249-1268, doi: 10.1007/s00445-008-0200-7.

Bonforte, A., Bonaccorso, A., Guglielmino, F., Palano, M., Puglisi, G. (2008) Feeding system and magma storage beneath Mt. Etna as revealed by recent inflation/deflation cycles. Journal of Geophysical Research 113, B05406. doi: 10.1029/2007JB005334

Bonforte, A., Gambino, S., Neri, M. (2009) Intrusion of eccentric dikes: The case of the 2001 eruption and its role in the dynamics of Mt. Etna volcano. Tectonophysics, 471: 78-86, doi: 10.1016/j.tecto.2008.09.028

Borgia, A., Ferrari, L., PasquarÃ¨, G. (1992) Importance of gravitational spreading in the tectonic and volcanic evolution of Mt. Etna. Nature, 357, 231-235, doi: 10.1038/357231a0

Bousquet, J.-C., Lanzafame, G. (2001) Nouvelle interprÃ©tation des fractures des Ã©ruptions latÃ©rales de l'Etna: ConsÃ©quences pour son cadre tectonique. Bulletin de la SociÃ©tÃ© GÃ©ologique de France, 172: 455-467, doi: 10.2113/172.4.455

Branca S. (2003) Geological and geomorphologic evolution of the Etna volcano NE flank and relationships between lava flow invasions and erosional processes in the Alcantara Valley (Italy). Geomorphology, 53, 247-261, doi: 10.1016/S0169-555X(02)00315-X

Branca, S., Del Carlo, P. (2005) Types of eruptions of Etna volcano AD 1670-2003: implications for short-term eruptive behaviour. Bulletin of Volcanology, 67: 732-742, doi: 10.1007/s00445-005-0412-z

Branca S., Coltelli M., Groppelli G. (2004) Geological evolution of Etna volcano. In: Bonaccorso, S., Calvari, S., Coltelli, M., Del Negro, C., Falsaperla, S. (Eds) "Etna Volcano Laboratory", American Geophysical Union Geophysical Monograph, 143: 49-63.

Calvari, S., Tanner, L.H., Groppelli, G., Norini, G. (2004) A comprehensive model for the opening of the Valle del Bove depression and hazard evaluation for the eastern flank of Etna volcano. In: Bonaccorso, S., Calvari, S., Coltelli, M., Del Negro, C., Falsaperla, S. (Eds) "Etna Volcano Laboratory", American Geophysical Union Geophysical Monograph, 143: 65-75.

Chester, D.K., Duncan, A.M., Guest, J.E., and Kilburn, C.R.J. (1985) Mount Etna, the Anatomy of a Volcano. London, Chapman and Hall, 404 p, http://books.google.it/books?id=qS6sAAAAIAAJ&printsec=frontcover&dq=Mou…

Coltelli, M., Del Carlo, P., Vezzoli, L. (1998) The discovery of a Plinian basaltic eruption of Roman age at Etna volcano, Italy. Geology, 26: 1095-1098, doi: 10.1130/0091-7613(1998)026<1095:DOAPBE>2.3.CO;2

Coltelli, M., Del Carlo, P., Vezzoli, L. (2000) Stratigraphic constraints for explosive activity in the last 100 ka at Etna volcano, Italy. International Journal of Earth Sciences, 89: 665-677, doi: 10.1007/s005310000117

Coltelli, M., Carlo, P., Pompilio, M., Vezzoli, L. (2005) Explosive eruption of a picrite: The 3930 BP subplinian eruption of Etna volcano (Italy). Geophysical Research Letters, 32, L23307, doi: 10.1029/2005GL024271

Corsaro, R.A., Cristofolini, R., and PatanÃ¨, L. (1996) The 1669 eruption at Mount Etna: Chronology, petrology, and geochemistry, with inferences on the magma sources and ascent mechanisms. Bulletin of Volcanology, 58: 348-358, doi: 10.1007/s004450050144

Corsaro, R.A., MÃ©trich, N., Allard, P., Andronico, D., Miraglia, L., Fourmentraux, C. (2009) The 1974 flank eruption of Mount Etna: An archetype for deep dike-fed eruptions at basaltic volcanoes and a milestone in Etna's recent history. Journal of Geophysical Research 114, B07204, doi: 10.1029/2008JB006013

Crisci, G.M., Avolio, M.V., Behncke, B., D'Ambrosio, D., Di Gregorio, S., Lupiano, V., Neri, M., Rongo, R., Spataro, W. (2010) Predicting the impact of lava flows at Mount Etna, Italy. Journal of Geophysical Research, 115, B04203, doi: 10.1029/2009JB006431

Del Carlo, P., Pompilio, M. (2004) The relationship between volatile content and the eruptive style of basaltic magma: the Etna case. Annals of Geophysics, 47: 1423-1432, http://www.annalsofgeophysics.eu/index.php/annals/article/view/4402

Doglioni, C., Innocenti, F., Mariotti, G. (2001) Why Mt Etna? Terra Nova, 13: 25-31, doi: 10.1046/j.1365-3121.2001.00301.x

Favalli, M., Tarquini, S., Fornaciai, A., Boschi, E. (2009) A new approach to risk assessment of lava flow at Mount Etna. Geology, 37: 1111-1114, doi: 10.1130/G30187A.1

Ferlito, C., Viccaro, M., Nicotra, E., Cristofolini, R. (2010) Relationship between the flank sliding of the South East Crater (Mt. Etna, Italy) and the paroxysmal event of November 16, 2006. Bulletin of Volcanology, in press, doi: 10.1007/s00445-010-0384-5

Gvirtzman, Z., Nur, A. (1999) The formation of Mount Etna as the consequence of slab rollback. Nature 401: 782-785, doi: 10.1038/44555

Herault, A., Vicari, A., Ciraudo, A., Del Negro, C. (2008) Forecasting lava flow hazards during the 2006 Etna eruption: Using the MAGFLOW cellular automata model. Computers & Geosciences, 35: 1050-1060, doi: 10.1016/j.cageo.2007.10.008

Kamenetsky, V.S., Pompilio, M., MÃ©trich, N., Sobolev, A.V., Kuzmin, D.V., Thomas, R. (2007) Arrival of extremely volatile-rich high-Mg magmas changes explosivity of Mount Etna. Geology, 35: 255-258, doi: 10.1130/G23163A.1

Lo Giudice, E., RasÃ , R. (1992) Very shallow earthquakes and brittle deformation in active volcanic areas: The etnean region as an example, Tectonophysics, 202: 257- 268, doi: 10.1016/0040-1951(92)90111-I

Mazzarini, F., Armienti, P. (2001) Flank cones at Mount Etna volcano: Do they have a power-law distribution? Bulletin of Volcanology, 62: 420-430, doi: 10.1007/s004450000109

Neri, M., Acocella, V., Behncke, B. (2004) The role of the Pernicana Fault System in the spreading of Mt. Etna (Italy) during the 2002-2003 eruption. Bulletin of Volcanology, 66: 417-430, doi: 10.1007/s00445-003-0322-x

Neri, M., Acocella, V., Behncke, B., Maiolino, V., Ursino, A., Velardita, R. (2005) Contrasting triggering mechanisms of the 2001 and 2002-2003 eruptions of Mount Etna (Italy). Journal of Volcanology and Geothermal Research, 144: 235- 255, doi: 10.1016/j.jvolgeores.2004.11.025

Neri, M., Guglielmino, F., Rust, D. (2007) Flank instability on Mount Etna: Radon, radar interferometry, and geodetic data from the southwestern boundary of the unstable sector. Journal of Geophysical Research, 112, B04410, doi: 10.1029/2006JB004756

Neri, M., Mazzarini, F., Tarquini, S., Bisson, M., Isola, I., Behncke, B., Pareschi, M.T. (2008) The changing face of Mount Etna's summit area documented with Lidar technology. Geophysical Research Letters, 35, L09305, doi: 10.1029/2008GL033740

Norini, G., De Beni, E., Andronico, D., Polacci, M., Burton, M., Zucca, F. (2009) The 16 November 2006 flank collapse of the south-east crater at Mount Etna, Italy: Study of the deposit and hazard assessment. Journal of Geophysical Research, 114, B02204, doi: 10.1029/2008JB005779

Pareschi, M.T., Boschi, E., Favalli, M. (2006) Lost tsunami. Geophysical Research Letters, 33, L22608, doi: 10.1029/2006GL027790

Puglisi, G., Bonforte, A., Ferretti, A., Guglielmino, F., Palano, M., Prati, C. (2008) Dynamics of Mount Etna before, during, and after the July-August 2001 eruption inferred from GPS and differential synthetic aperture radar interferometry data. Journal of Geophysical Research, 113, B06405, doi: 10.1029/2006JB004811

Rittmann, A. (1964) Vulkanismus und Tektonik des Ãtna. Geologische Rundschau (now International Journal of Earth Sciences), 53: 788- 800, doi: 10.1007/BF02054564

Rust, D., Neri, M. (1996) The boundaries of large-scale collapse on the flanks of Mount Etna, Sicily. In: McGuire,W.C., Jones, A.P., Neuberg, J. (Eds) "Volcano Instability on the Earth and Other Planets", Geological Society of London Special Publications, 110: 193-208, doi: 10.1144/GSL.SP.1996.110.01.15

Rust, D., Behncke, B., Neri, M., Ciocanel, A. (2005) Nested zones of instability in the Mount Etna volcanic edifice, Sicily. Journal of Volcanology and Geothermal Research, 155: 137-153, doi: 10.1016/j.jvolgeores.2004.11.021

Schellart, W.P. (2010) Mount Etna-Iblean volcanism caused by rollback-induced upper mantle upwelling around the Ionian slab edge: An alternative to the plume model. Geology, 38: 691-694, doi: 10.1130/G31037.1

Schiano, P., Clocchiatti, R., Ottolini, L., BusÃ , L. (2001) Transition of Mount Etna lavas from from a mantle-plume to an island-arc magmatic source. Nature, 412: 900-904, doi: 10.1038/35091056

Schmincke, H.-U., Behncke, B., Grasso, M., Raffi, S. (1997) Evolution of the northwestern Iblean Mountains, Sicily: uplift, Plicocene/Pleistocene sea-level changes, paleoenvironment, and volcanism. Geologische Rundschau (now International Journal of Earth Sciences), 86: 637-669, doi: 10.1007/s005310050169

Spilliaert, N., Allard, P., MÃ©trich, N., Sobolev, A. (2006. Conditions of ascent, degassing and eruption of primitive alkali basalt during the powerful 2002 flank eruption of Mount Etna. Journal of Geophysical Reserarch, B04203, doi:10.1029/2005JB003934

Tanguy, J.-C., Condomines, M., Kieffer, G. (1997) Evolution of the Mount Etna magma: Constraints on the present feeding system and eruptive mechanism. Journal of Volcanology and Geothermal Research, 75: 221-250, doi: 10.1016/S0377-0273(96)00065-0

Tommasini, S., Heumann, A., Avanzinelli, R., Francalanci, L. (1997) The fate of high-angle dipping slabs in the subduction factory: an integrated trace element and radiogenic isotope (U, Th, Sr, Nd, Pb) study of Stromboli Volcano, Aeolian Arc, Italy. Journal of Petrology, 48: 2407-2430, doi:10.1093/petrology/egm066

Walter, T., Acocella, V., Neri, M., Amelung, F. (2005) Feedback processes between magmatic events and flank movement at Mount Etna (Italy) during the 2002-2003 eruption. Journal of Geophysical Research, 110, B10205, doi: 10.1029/2005JB003688

eklemetti Thu, 08/19/2010 - 22:05

Tags

Etna

Galeras

guest blogger

italy

Etna Week (Part 2) - The current dynamics and activity of Etna

eklemetti — Wed, 18 Aug 2010 04:14:53 +0000

Etna Week (Part 2) - The current dynamics and activity of Etna

This is Part 2 of 3 from guest blogger Dr. Boris Behncke. Check out Part 1 here.

The current dynamics and activity of Etna
by guest blogger Dr. Boris Behncke

The recent behavior of Etna is characterized by nearly continuous eruptive activity from the summit craters and eruptions from new vents on the flanks at intervals of a few years to decades. Summit eruptions vary from quiet lava emission to mild Strombolian explosions to high-discharge-rate Hawaiian to sub-Plinian style lava and fire fountaining accompanied by the emplacement of fast-moving lava flows; usually the strongest activity concentrates in episodes lasting from a few tens of minutes to a few hours. Most flank eruptions are predominantly effusive - that is, characterized by the emission of lava flows, and explosive activity during these events is often limited to Strombolian explosions or mild spattering. This leads to the emplacement of extensive lava flow-fields and only minor cones are built at the eruptive vents, including the smallest constructive volcanic features, called hornitos (Spanish: "small furnaces").

Pyroclastic constructs on Etna come in all forms and sizes. The photograph at top shows a cluster of steep, narrow spires a few meters tall built up around small vents by the ejection of liquid blobs of lava (spattering activity), seen against the backdrop of the huge composite cone of the Southeast Crater, one of the summit craters of Etna. The conspicuous yellow hue is from sulfur deposits. The bottom photograph shows the largest pyroclastic flank cone formed during the historical period, Monti Rossi at about 700 m elevation near the village of Nicolosi, on the south flank of Etna. The name, literally, means "the red mountains" - the plural stands for the two summit peaks, the crater actually lying between them; but the original name - Monte della Ruina, "mountain of devastation" - more accurately refers to the catastrophic impact of this eruption. The cone is approximately 250 m tall from base to top. Photos taken in 1999 and 2000 by Boris Behncke

Some flank eruptions, however, show much more intense explosive activity, like the 2001 and 2002-2003 eruptions, and a number of previous eruptions as in 1852-1853, 1879, 1886, and 1892. Conspicuous pyroclastic cones (also called cinder cones or scoria cones) are formed during such explosive activity, which can be up to a few hundred meters tall, like the prominent double-peaked Monti Rossi cone formed during the unusually voluminous and explosive 1669 eruption on the south flank of Etna. A typical feature of the flank vents is that each erupts only once, like the eruptive centers in monogenetic cone fields worldwide (e.g., the famous "new volcano" ParÃcutin in Mexico, 1943-1952). As a matter of fact, the numerous pyroclastic cones of Etna could be considered a monogenetic cone field, were it not for the huge central volcano on whose flanks they are sitting.

Flank eruptions represent a considerable hazard for the populated areas on the lower flanks of the mountain, which are home to approximately one million people. During the historical period, new flank vents have occasionally opened within those areas that are now densely urbanized, especially on the southern and southeastern flanks, most recently in 1669 near the village of Nicolosi. During the past 1000 years, lava flows have reached the coast of the Ionian sea on three occasions, in ~1030, 1224, and 1669. The map below shows the extent of historical lava flows, distinguishing those of flank eruptions (in different shades of pink, yellow and red) from those emitted during summit eruptions (in green). It is evident that summit lava flows have never come anywhere close to the populated areas and therefore summit activity poses no immediate threat to those areas.

Map of historical lava flows of Etna, distinguishing summit from flank eruptions. Modified from Crisci et al. (2010)

Evolution of the summit area
The summit area of Etna has undergone profound changes in the past century. Until 1911, there was a single large crater at the summit, about half a kilometer wide, and truncating a broad cone about 300 m tall, which had grown since a major summit collapse accompanying the large 1669 flank eruption. This crater was known as the Central Crater. At the beginning of the 20th century, it was a funnel-shaped pit about 200 m deep, but intermittent eruptive activity on its floor led to its gradual filling, and in the mid-1950s, lava flows for the first time overflowed from the Central Crater onto the upper flanks of the volcano. Vigorous activity from several vents within the crater in the early 1960s led to the complete filling and obliteration of the Central Crater, and two large cones built up around the two main vents, the Voragine ("Big Mouth") that had been present since 1945, and a smaller vent known as "the 1964 crater". In 1968, a third vent opened, which became known as Bocca Nuova ("New Mouth"), and which progressively enlarged in diameter mostly due to the caving in of its unstable rims.

For much of the 1970s to 1990s, the evolution of the Voragine and the Bocca Nuova was characterized by periodic intracrater activity and rim collapse, leading to their growth in diameter, until the two pits began to coalesce with only a thin septum remaining between the two, known as the "diaframma" (diaphragm). During a period of exceptionally intense summit eruptions in 1997-1999, both craters were filled to overflowing before subsidence of magma in their conduits led to the formation of new collapse pits, which gradually enlarged and coalesced into a single large depression, Etna's new Central Crater.

Aerial views of Etna's summit area showing the evolution from the single Central Crater in the early 20th century to the currently four summit craters. Top photograph was taken in the 1920s, when the Northeast Crater was already present (but is barely discernible in this view); the size and depth of the Central Crater is well recognizable here. The view is from the west. Center photo is of 1961 and shows the Central Crater filled-to-overflow with pyroclastic cones and lava; the much smaller Northeast Crater is seen behind the Central Crater to the left. The view is from the south. Photograph at bottom was taken in May 2008, the Bocca Nuova and Voragine are in the upper center, nearly coalescing into a new Central Crater, whereas the Northeast Crater is emitting a dense white vapor plume at right, and the Southeast Crater is at center left, showing conspicuous light-colored sulfur deposits lining its rim. The view is from the east. Photographers for top and center photographs unknown, bottom photo by Stefano Branca (INGV-Catania)

In the spring of 1911, a collapse pit opened at the northeastern base of the central summit cone, from which issued a vapor plume but which showed no eruptive activity until 1917. This pit became known as "the Northeast subterminal Crater" (the term subterminal is applied to eruptive vents lying close to Etna's summit craters and showing a eruptive behavior different from the vents of flank eruptions); it is now called Northeast Crater. The new crater remained a pit until 1923, when a small cone grew within and filled the pit, leading to the first lava overflows from the Northeast Crater. In the 1950s, cone growth intensified, as the crater became the site of virtually continuous, mild Strombolian activity accompanied by slow lava emission; this type of activity was termed "persistent" and for a long time was believed to represent the most common type of Etnean eruptive manifestation. In 1977, however, the Northeast Crater switched to a more dramatic form of volcanism, which proved highly efficient in making it become the highest point on Etna - brief but violent episodes of high lava fountaining with voluminous, fast-moving lava flows and tall tephra columns.

The Northeast Crater showing different types of eruptive activity. Top photo, taken in 1969, shows the cone of the Northeast Crater nearly as tall as the rim of the former Central Crater (in the foreground), and displaying weak Strombolian activity from its summit, while lava quietly issues from a small crack on the left side of the cone. This activity lasted with few interruptions from 1955 until 1971, and again from 1974 until 1977. Photographer T. Micek (?). The bottom photograph shows one of about twenty episodes of violent fire fountaining and tall tephra plumes that occurred between July 1977 and March 1978; this was one of the latest episodes of that series. View is from the village of Monterosso on the southeast flank of Etna, photo by Carmelo Sturiale.

By 1978, the Northeast Crater had grown to about 3340 m elevation and thus become the highest point ever measured on Etna. It produced a few more episodes of lava fountaining in late-1980 and early-1981, which brought its height to 3350 m. On 24 September 1986, an unprecedentedly violent eruptive episode caused a reduction in height by 10 m of its cone, and further collapse occurred throughout the following decade. Although the Northeast Crater went through another phase of intense activity in 1995-1996, its height continued to decrease, and in 2007 was 3329.6 m (Neri et al., 2008).

The Southeast Crater seen from the air immediately after its formation in spring 1971 (top) and in May 2008 (bottom). Note that the field of view in the latter photo is much wider than in the earlier. Photos taken by Carmelo Sturiale and Boris Behncke

The latest addition to Etna's summit crater family is the Southeast Crater, which formed during a flank eruption in May 1971 at the southeastern base of the central summit cone as a sort of pressure valve - while lava was emitted a few kilometers further downslope to the northeast, it emitted vapor-rich ash clouds for a couple of weeks. It then remained quiet until spring 1978 and then sprang to life with high lava fountains accompanying a series of flank eruptions in rapid succession - April-June, August, and November 1978, and August 1979. Since then, it has been the most persistently active vent on Etna, and its appearance on the stage was accompanied by a marked change in the eruptive behavior of the volcano. As a matter of fact, since the birth of the Southeast Crater, Etna has practically doubled its average output rate (Behncke and Neri, 2003a).

The Southeast Crater has grown much more rapidly than the Northeast Crater, and nearly 40 years after its birth its cone stands approximately 300 m above the site where it came to life in 1971, reaching a height of 3290 m as of 2007. This rapid growth is the result of numerous periods of frantic eruptive activity which are unparalleled in the documented history not only of Etna but of all volcanoes on Earth. The culmination was a series of 64 episodes of violent lava or fire fountaining between January and June 2000, followed by two more in August and 16 more in May-July 2001 (Behncke et al., 2006). The Southeast Crater has erupted more recently in 2006 and 2007-2008, again producing numerous episodes of strong Strombolian activity and lava fountaining, the latest - and possibly most violent - on 10 May 2008, when lava flows advanced 6.4 km in 4 hours, an unprecedented value for Etnean summit eruptions.

What are the reasons for such variable and, for a basaltic volcano, often unusually violent explosive behavior?

Eruption types and styles
It seems that much of the explosivity of Etna is driven by magmatic gases, foremost water vapor (H₂O) and carbon dioxide (CO₂). Etna is emitting significant quantities of these gas species, up to 200,000 metric tons of water vapor and about 20,000 tons of carbon dioxide per day. Eruptions tend to be more explosive when magma rises fast, which is the case when batches of new primitive magma enter into the plumbing system of the volcano, so that the most explosive eruptions of Etna in the past few thousand years have also produced the most mafic magmas (Coltelli et al., 2005; Kamenetsky et al., 2007). In particular, a powerful sub-Plinian eruption about 3930 years before present produced picritic magma, which was also extremely enriched in CO₂. In contrast, the Plinian eruption of 122 BC was apparently triggered by the sudden decompression of the magmatic system, which led to the catastrophic exsolution of gas although the pre-eruptive water content of the magma was found to be only about 1 weight-% (Del Carlo and Pompilio, 2004).

Hypothetical and simplified scheme of the magmatic plumbing system of Etna, illustrating magma transport feeding summit activity and the two different types (lateral vs. eccentric) flank eruptions, from Behncke and Neri (2003b)

Most magma ascends to the surface through the central conduit system of Etna, which leads to the frequent summit activity. Unless magma ascent is very rapid, much gas is lost from the magma during its ascent to the surface, and significant volumes of relatively gas-poor magma are stored in the shallow plumbing system of the volcano. During many flank eruptions of Etna, such gas-poor magma exits laterally from the central conduits, resulting in relatively weak or almost no explosive activity but copious lava outflow. Most flank eruptions during the 20th century were of this type; they are commonly called "lateral" flank eruptions. Typically such eruptions are accompanied by the cessation of summit activity and some collapse at the summit craters, as the central conduit system is drained of magma.

Extremes in eruptive styles at Etna: totally non-explosive extrusion of gas-poor lava near the Southeast Crater in 1999 (top), and the 10-km-high eruption column formed during a sub-Plinian eruption from the Voragine on 22 July 1998 as seen from Catania. Photos taken by Boris Behncke and Sandro Privitera

Another type of Etnean flank eruption is characterized by much more pronounced explosive activity, resulting in the emission of significant volumes of ash even for prolonged periods of up to several months, as in 1892, 2001, and 2002-2003. These eruptions occur when magma, rather than rising through the central conduits, pushes its way forcefully through the flank of the volcano to form new conduits called "eccentric" or "peripheral" (Rittmann, 1964; Neri et al., 2005). Being in a closed system until eruption, the magma does not lose significant amounts of its gas during ascent, and therefore the ensuing activity is considerably more explosive. The 1974 and 2002-2003 eccentric eruptions did in fact produce more tephra than lava (Andronico et al., 2004; Corsaro et al., 2009), belying the widespread notion of Etna being a rather non-explosive volcano!

Eruptions and flank instability
The question why Etna makes flank eruptions at all is not easy to answer. Certainly the fact that the volcano lies above the intersection of several main regional fault systems helps in rendering its flanks unstable and subject to fracturing. Mazzarini and Armienti (2001) demonstrated that the distribution of Etna's flank cones is largely controlled by intersections between tectonic lines of weakness. It has also been suggested (e.g., Chester et al., 1985) that the hydrostatic (or rather "magmastatic") pressure exerted on the conduit walls by the rising magma column within the conduit might lead to the opening of lateral cracks through which the magma could escape to feed flank eruptions. Bousquet and Lanzafame (2001) specified that magma transfer from the central conduits into the flank occurred in a more or less horizontal manner, rather than rising upward vertically. All of these scenarios concerned exclusively lateral flank eruptions, not eccentric ones, which had effectively been nearly forgotten prior to the 2001 and 2002-2003 eruptions.

The Pernicana fault cuts through the northeastern flank of Etna, from an elevation of about 2000 m at the Northeast Rift, down to sea level near the village of Fondachello. From Neri et al. (2004)

Displacement along the Pernicana fault during the massive flank movement of 2002, along the Fornazzo-Linguaglossa road (top) and the Catania-Messina highway (bottom). From Neri et al. (2004)

Since the early 1990s scientists (Borgia et al, 1992; Lo Giudice and RasÃ , 1992; Rust and Neri, 1996; Bousquet and Lanzafame, 2001) proposed that a large portion of the volcano, encompassing its eastern and southern flank sectors, was subject to lateral sliding, much in the same manner as the southern flank of KÄ«lauea on Hawai'i. There was some debate as for the cause of the sliding - was it caused by gravitational pull, the push of accumulating magma below the volcano, or by more shallow intrusion of magma into the flanks? Also the extent of the mobile sector was not unanimously defined; whereas there was agreement that the northern boundary of this sector was defined by the transcurrent (mostly horizontally moving) Pernicana fault, the southern or southwestern boundary was variously attributed to different fault systems cutting the southeastern and southwestern flanks of Etna. It is now known that the extreme southwestern boundary is the Ragalna fault system (Rust and Neri, 1996; Rust et al., 2005; Neri et al., 2007).

Speculation became truth in the fall of 2002, when a large sector of the eastern and southeastern flank of Etna underwent a massive move toward the Ionian Sea. During a powerful and complex flank eruption in the summer of 2001, the southern flank and summit area of the volcano were violently ripped open, and the eastern flank started to move away from the remainder of the mountain at accelerating speed. Though this was recognized only in hindsight (Bonforte et al., 2008, 2009; Puglisi et al., 2008), many of us were convinced that the 2001 eruption had significantly destabilized the volcanic edifice, and that further flank eruptions would occur from now on in rapid succession.

On 24 September 2002, a shallow earthquake occurred on the northeast flank of Etna, along the upper portion of the Pernicana fault system, which had been very active during the 1980s but had not shown any seismic activity or significant displacement since 1988. The earthquake was accompanied by conspicuous ground rupturing along the fault, similar to numerous events between 1980 and 1988. A few weeks later, on 27 October 2002, a more pronounced movement along the fault heralded the onset of a new flank eruption, which affected both the south and northeast sides of Etna and destroyed numerous tourist facilities as well as forested areas. During a few days, a part of the northeastern flank moved by more than 2 m eastward; then the movement extended over an ever larger area to the southeast side of Etna, where earthquakes accompanying the displacement caused severe damage in several villages, such as Santa Venerina and Milo.

Top: The sector of Etna's eastern to southern flanks affected by flank instability and displacement is shown in pink. PFS = Pernicana fault system; VB = Valle del Bove; RN = Ripe della Naca; ZE = Zafferana Etnea; SV = Santa Venerina; TFS = Timpe fault system; AC = Acireale; TF = Trecastagni fault; R = Ragalna fault system. From Neri et al. (2004). Bottom: Distribution of earthquake epicenters accompanying the 2002 eruption and flank movement helped to distinguish several blocks (Blocks 1, 2 and 3) within the unstable sector, moving at different times and speeds. From Neri et al. (2005)

This immense mass movement, which was later revealed to have involved about 2000 cubic kilometers of rock (Walter et al., 2005), both of the volcanic pile and of the underlying sedimentary basement, was documented in extreme detail, thanks to improved monitoring equipment placed on the volcano a few years before. It could thus be established that the movement started at the Pernicana fault in the northwestern portion of the moving sector, and then extended both eastward - to the Ionian coast - and southward, affecting numerous fault systems cutting through the eastern and southeastern portions of the volcano. In the entire area, earthquakes were strongly felt and often caused damage, and cracks ripped through buildings and other constructions as well as roads.

Since the fall of 2002, the movement of Etna's eastern flank has continued, most of the time at somewhat reduced speed, but often with new accelerations accompanied by shallow earthquakes. Since 2004, the southern block in the unstable sector has started moving slowly southward. At the Pernicana fault, dramatic slip accompanied by earthquakes and rupturing of the ground surface has occurred several times in 2003 and 2004, and again in early April 2010. This all indicates that the volcano has not yet returned to a state of relative stability and equilibrium as before 2002 (or 2001, if we consider the eruption of that year a significant factor in destabilizing the volcano). As a matter of fact, the behavior of Etna has changed profoundly since 2001.

Fluctuations in Etna's eruptive behavior since 1600 AD, with marked variations in the frequency, style, and size (volume) of eruptions. The output rate was exceptionally high from about 1607 until 1669, when ten - most of them very large - flank eruptions occurred (see black vertical bars in the graph at the bottom of the figure) and up to 3 cubic kilometers of magma was erupted. Very low output and few flank eruptions are seen during the following ~100 years, until the 1760s when flank eruptions pick up in frequency and size. A marked acceleration in the activity of Etna is evident starting in the second half of the 20th century. Unpublished figure by Boris Behncke and Marco Neri

Eruptive cycles
If one looks at the historical record of Etna's eruptions, it becomes evident that the intervals between these events, as well as their characteristics (duration, location, volume, eruptive style) vary strongly. Unfortunately the record is complete only since the beginning of the 17th century, yet these past little more than 400 years show remarkable fluctuations in Etna's activity. The first 70 years of the 17th century showed unusually high levels of activity, with frequent summit activity and ten flank eruptions. Some of these flank eruptions lasted for years - the one of 1614-1624 being the longest flank eruption in the historical record of Etna - and produced large volumes of lava (1614-1624: about 1 km3, 1634-1638: about 200 million m3, 1646-1647: about 160 million m3, 1651-1653: about 450 million m3, 1669: about 650 million m3). A few of the flank eruptions were quite explosive and built large pyroclastic cones, like Monte Nero during the 1646-1647 eruption and Monti Rossi in 1669.

The last eruption in this series, in 1669, apparently emptied a shallow magma reservoir that had existed throughout the previous decades - evidence for such a reservoir lies in the presence of abundant up to centimeter-sized plagioclase feldspar crystals in the lavas of all eruptions from 1600 until 1669. The rounded shape and pale yellow color of these crystals has led the locals to call the lavas of this period "cicirara", which means something like "chickpea lava", because the crystals resemble chick peas! Due to a prolonged presence in a reservoir relatively close to the surface, the magma could cool and crystallize to the degree that plagioclase grew to the "chick pea" size crystals seen in the 17th century lavas. Further evidence for wholesale magma extraction from a shallow reservoir and a dramatic withdrawal of the magma column in the central conduit is the collapse of Etna's summit cone during the 1669 eruption (Corsaro et al., 1996).

After the 1669 eruption, Etna has never again produced "cicirara". Furthermore, the frequency and size of flank eruptions dropped sharply for about 100 years, with only three minor flank eruptions being recorded in 1689, 1702, and 1755. It seems that the magma reservoir that had fed the intense activity of the 17th century had disappeared, the feeding system of the volcano had been disrupted, and the mountain had become structurally stable. Much of the time, all magma that made it to the surface rose to the summit, where a new cone was constructed. Flank eruptions became frequent again from 1763 on, and for the next 100 years occurred about once per decade, with volumes of a few tens to rarely more than 100 million cubic meters per eruption.

Interestingly, throughout the 18th and the first half of the 19th centuries, there are no records of significant earthquakes in the unstable eastern sector of Etna as those of the 1980s and of 2002 and the following years. A powerful and destructive earthquake in 1818 near Acireale was probably caused by movement along a regional tectonic fault, not by movement of Etna's unstable flank.

Etna's unstable eastern to southern flank sector, and a selection of earthquakes presumably caused by movement of this unstable sector. Note that there have been many more earthquakes in this area during the period since 1865, when the first of these events took place. Unpublished figure by Boris Behncke

Then came the year 1865, which brought a large eruption on the northeast flank - the Monti Sartorius eruption - and soon after its end, a very localized, extremely shallow (close to the surface) earthquake on Etna's eastern flank, which devastated the village of Macchia di Giarre and killed about 70 people. Similar earthquakes have since then occurred at a recurrence rate of a few years, luckily rarely resulting in as many fatalities, but often causing significant damage and a few human deaths. Most, if not all, of these earthquakes are now known to be related to slippage, or movement, of Etna's unstable eastern to southern flank sectors.

At the same time, the intervals between flank eruptions have become systematically clustered into determined sequences, or parts of cycles. The first cycle started after the large 1865 flank eruption (and the first earthquake in modern time that can be with confidence attributed to flank displacement), initially with quiet emission of gas from the Central Crater and a few years later, mild activity within the Central Crater. From 1874 until 1892 there were five flank eruptions, which showed an overall increase in emitted volume in time, the latest - in 1892 - being the most voluminous (besides 120 million m3 this eruption also produced a significant amount of pyroclastics). This increase in the volume of flank eruptions was apparently the result of increasing structural instability of the volcano. Apparently the emission of a large volume of magma brought this cycle to a close, the volcano returned to relatively stable conditions, and a new cycle started, like the previous one, with a period of quiescence, followed by summit activity, which in turn was followed by a further series of flank eruptions. Four cycles of this type occurred between 1865 and 1993. The latest of these was longer than its predecessors - 42 years - and culminated in a series of no less than 13 flank eruptions, many of which were among the largest of the past 300 years. This cycle ended with the 472-days-long eruption that lasted from December 1991 until March 1993 and produced the greatest lava volume - about 250 million cubic meters - of any Etnean eruption since 1669.

Evolution of the 1952-1993 eruptive cycle at Etna, showing three main phases (Eruptive quiescence -> summit activity -> flank eruptions, ending with a particularly voluminous flank eruption). Unpublished figure by Boris Behncke and Marco Neri

Interestingly, there was very little seismic activity in Etna's unstable sector during the first two phases of this cycle, whereas they became more and more frequent during the third phase. Many episodes of accelerated flank displacement preceded flank eruptions by days to months, as in 1981, 1983, 1985, and 1989.

Etna's latest and ongoing cycle started after the end of the large 1991-1993 flank eruption. For two years, no eruptive activity occurred anywhere on the mountain. Then, in summer 1995, eruptive activity returned to the summit craters - first at the Bocca Nuova and then at the Northeast Crater; in 1996 and 1997 also the Southeast Crater and the Voragine joined the party (Allard et al., 2006). This period of summit eruptions continued until July 2001 and consisted of several long-lasting lava overflows and more than 150 episodes of violent Strombolian to sub-Plinian explosive activity, nearly always with copious lava emission. We called this exceptional period of activity "The Millennium Fireworks". Still more exciting fireworks came with the flank eruptions of 2001 and 2002-2003, and two more flank eruptions have occurred in 2004-2005 and 2008-2009, separated by a period of spectacular eruptions from the Southeast Crater in 2006-2008. These events are described in detail in the Bulletins of the Global Volcanism Network (scroll down the page to get to the more recent reports).

What should be noted is that since flank eruptions kicked in again in 2001, the unstable flank sector of Etna has moved at sometimes astonishing rates (up to several tens of centimeters in a few days in spring 2009), and seismic activity in this sector has been intense, including a series of rupturing events at the Pernicana fault as recently as April 2010. The volcano seems to be currently in the middle of an eruptive cycle, and it is likely that this will come to an end (and bring back the volcano to a state of temporary stability) only with a very large, voluminous flank eruption (Behncke and Neri, 2003a; Allard et al., 2006). From a scientific point of view this is rather exciting. From a human (and civil defense) point of view, these prospects are rather disconcerting and challenging.

So why does the flank of Etna move? It is now believed that much of the movement is caused by the pressure of magma accumulating within the volcano. As a matter of fact, much more magma enters into Etna's plumbing system than exits during eruptions. The quantity of this unerupted "excess" magma can be approximately calculated from the amounts of gas emitted from the volcano, in particular sulfur dioxide. It has thus been revealed (Spilliaert et al., 2005; Allard et al., 2006) that at least three-quarters of the magma that enter into the Etnean feeder system stay there, which leads to a constant volume increase. Where does all this magma go? There are certainly no empty spaces that can host this magma, so space must be created, and this is best done in pushing the volcano, both upwards (so that the volcano swells, or inflates), and sidewards, in whatever direction the side of the mountain gives way most easily. At Etna this is on the eastern, southeastern, and to a lesser degree, southern flanks, which are not buttressed by surrounding mountains as the northern and western flanks. It can be speculated that the more magma accumulates below the volcano, the more unstable it becomes, and this in turn facilitates the opening of fractures on the flanks, allowing magma to escape in flank eruptions. Possibly the presence of a large, relatively shallow magma reservoir during the 17th century led to a strong destabilization of the volcano, which thus had magma leaking through its open flanks on any given occasion, and in large volumes. A similar situation seems to be on the way to become established in recent decades - so no one would be really surprised to see Etna behave again like it did between 1600 and 1669, but once more, these are anything else than comforting prospects.

eklemetti Wed, 08/18/2010 - 00:14

Tags

Very interesting.

I was just wondering, is a catastrophic flank failure at all likely?

Outstanding work Dr. Behncke! Thank you so much for publishing this to the impressed hobby-volcanologists!

"...much more magma enters into Etna's plumbing system than exits during eruptions."
This is, to me, a stunning revelation.
1. Do you believe that a massive failure of the southeastern slopes could take place, in a similar way as it did in Mt. St. Helen's?
2. Is ice accumulation, in winter, heavy enough to affect the stability of big fat Mamma Etna?
3. If you pick Etna and covers it with a huge Icecap (like in VatnajÃ¶kull, in Iceland) what would happen? Could we compare processes in Badarbunga system with Etna's?
It's getting more and more interesting and enlightening.
Thank you Boris.

@Gareth #1 and Renato Rio #3 - currently a catastrophic flank failure seems unlikely, because the stress on the eastern flank sector is released in numerous small slip episodes and nearly continuous, slow, aseismic creep. This is similar to the flank slip at Kilauea, and some publication (I admit I don't remember which one) recently proposed that basaltic volcanoes such as Kilauea, Etna, and Piton de la Fournaise are capable of accomodating their flank instability in numerous and frequent minor episodes rather than collapsing catastrophically. Obviously, catastrophic collapse does occur (it is well documented for the Hawaiian volcanoes and the Valle del Bove collapse at Etna seems pretty much ascertained by now) but more rarely.

Ice and snow accumulation are currently relatively minor at Etna - virtually all snow melts during the summer - but minor quantities of ice can be preserved under tephra if this is deposited on snow during the winter as in early 2000 and late 2002. The quantities of ice do not appear to be significant in affecting the volcano stability. However, a few thousand years ago this might have been different - a group of British scientists (Deeming, McGuire and Harrop) recently proposed that the Valle del Bove collapse was triggered by magma intrusion into water-saturated flanks during cooler and wetter weather conditions.

We know that Etna was covered with glaciers before the cataclysmic "Ellittico" eruptions 15,000 years ago. The presence of the glaciers certainly led to much more explosive volcanism than has occurred since then. However, this is an area of ongoing studies and much more needs to be revealed.

Boris,

I lived on Etna (in Nicolosi) from 1993 to 1996. I was able to witness it "re-awaken" from its slumber following the huge 1989-1993 lava eruptions. I used to go up to the fractures produced by the initial 1989 intrusions which cut the roadway to the ski area (as I remember!). At times, while I was at the fractures, the guardrails would abruptly begin to creak and pop, I believe due to further intrusion and spreading going-on beeath that area. so i had my own makeshift strainmeters! Upon returning to my home, following one particularly noisy/active visit to the fractures, the Northeat Crater erupted!
By the way,...another outstanding presentation of your knowledge of Etna volcanology!

Thank you Boris,especially for the information about flank stability. It never even crossed my mind that Catania on the sea may be in a fault/slip zone.

What an amazing volcano.

Stupendous.

Boris,

that was a fantastic presentation! I was watching some of what was going on, too, and that made it all the more interesting for me to read. I can hardly wait for the next installment! I can see why you chose to study Etna because it is a facinating mountain with some interesting seizmic zones along with the volcanic mechanisms.

From the illustration of Behncke and Neri (2003b) it looks like some fault blocks on the north-east area and I am wondering if it is part of the flank collapse or fault blocking.

I remember the quake that offset the roads and did so much damage and watched as the Piano de Lago disapeared. That was such a beautiful area before the eruption that covered so much of it. But there is beauty even in the lava flows just like the area around Mt. St. Helens and Mt. Lassen. It is amazing how things can recover so quickly and something else that I have found interesting is the fact that around Mt. St. Helens, there has been fossilization found already! I think that has blown the scientific world's mind. I will look forward to the day when some recovery will be evident in the Piano de Lago area. It will take a while, but I bet it will come back faster than we ever thought possible. Of course, it depends on Etna's activity. It could send more lava down that way.

Has there been any indication of an eruption taking place any time soon? Maybe you will be talking about that in your next post.

Thanks so much for taking the time to teach us about Etna and the complexities of the inner workings of a volcano not fully understood. Interesting stuff.

just a random thought ...

a large active sill type magma chamber extension in the E / SE would have a very high "lubricating" effect on the movement ? no ??

sort of like trying to walk on a sea of ball-bearings ???

I am in awe..I feel like saying "we are not worthy". Almost reluctant to ask what are probably rather silly questions, but:

Re the 'chick-pea' lavas: surely basalt magma held "in storage" for some time would first crystallise olivine? Are there olivine phenocrysts? Or did this mineral sink under gravity, so that somewhere in Etna's guts there are olivine cumulate lenses? (left after the bulk of that magma body had erupted)

Second: I read a while back (in a press story, so a dubious source) that recent Etna lavas had been found to contain amphibole, for the first time in many years. Is this so, and is it related to the recent changes in behaviour?

Third (more relevant to part 1, sorry); how does the historically active Campi Flegrei del Mar Sicilia (sp?) SW of Sicily fit into the plate-tectonic scheme for the Etna/Sicily area?

#10 @Mike Don
Your third question also came to my mind. I was curious to understand the tectonics under both Campi Flegrei Mar Sicilia and Pantelleria. The latter is explained as being "continental rifting" (!?)(SMI Global Volcanism Program)but they don't mention any correlation between the two volcanoes. Could Campi be a continuation of Calabric Arc? Could there be another segment of subducting oceanic lithosphere underneath? Or another "slab rollback" to the W? I have been doing some research over the web, but all I could find was this abstract from an article concerning the Lipari-Vulcano Volcanic System (LVVC):

"...the LVVC crustal structure and the evolution of the volcanism are consistent with those recognized in zones of transition from arc-related to rift volcanism. In addition, results of a preliminary mechanical analysis based on the available structural data indicate low values of the ratio between magmatic overpressure and tectonic stress. This suggests a passive mechanism of mantle upwelling. The mantle upwelling is due the post-collisional normal strikeâslip tectonics affecting the Aeolian Arc."

http://www.sciencedirect.com (link to big to be pasted)

Since the LVVC is further NE I don't know if has any relation to Campi and Pantelleria, both only 70 km apart.
When Boris said "the geodynamic setting of Etna is a bit complicated" he really meant it.
Any clues, Boris?

@Mike: I also found a very interesting book on the subject through Google Books:
"Postcollisional tectonics and magmatism in Mediterranean region and Asia, by Yildirim Dilek,Spyros Pavlides (you can read parts of it):
Here's a transcript:
"These features collectively suggest that the fault pattern observed in the Sicily channel may result from coexistent deformation regimes, with NE-SW-directed extension superimposed on the subduction-related NW-SE-directed compression in the Maghrebides (?), Sicily and the Apenines. The case history of the Sicily channel indicates that continental and extensional processes can overlap in the same area. Moreover, the coexistence in this central Mediterranean area of two deformational settings suggests that plate boundaries are passive features rather than the driving mechanisms of plate tectonics."
Isn't that awesome?

I'm still trying to get my head around just how big this volcano is.

http://i34.tinypic.com/2n9jl34.png

@Lurking
Fantastic plot! You can almost see the magma pushing up through the "slab-rollback-created-window". And yes. It is huge. Good job!
I suggest that everyone tried some Google-earthing over Sicily. And also over Pantelleria. Don't miss the pictures attached - you can see the most extraordinary rock formations near the southern edge of the island.
And then you all understand why Boris is so happy in this geological paradise.

Okay... I have more faith in these profile quake plots.

View North

http://i33.tinypic.com/8ys4dz.png

View East

http://i38.tinypic.com/2mq0pow.png

Note how the quakes tend to veer off to the East as they get shallower. (compare the two views)

View North is one degree across, View East is 0.5 degrees across.

#15 You mean, like in an ascending helical? Interesting...

Fantastic article, Boris, thanks! When will you write the definitive book on Etna?

@Lucky #13: what strikes you as odd about the topology?

Other Etna data graphs of interest:

1. Using the Volume vs Time chart, if one goes to the Wikipedia Little Ice Age entry and captures the past portion of the temperature plot (1600-2004) and superimposes a semi-transparent image over the TvV chart, very nice correlation may be found in the rate change over time.

2. Using the 'example of a cycle' chart, and superimposing upon it a portion of the 'Global Temperature Record' (also a wikipedia graphic), again, we see an interesting correlation between phases and temperature.

So what is going on here? We got a hint, in Boris' comment above, that one of the phases of activity *may* be correlated to Ice Age recession of Etna glaciers at existed during the Dryas period of icecap recession.

We think temperature glacier rebound, centered just below Switzerland where large icecap fragments once existed and glacier recession is much in evidence, and change in Mediterranean sea level during recent hemispheric cooling (LIA, within the last 400 years) might be factors at work in 'loading' aesthnosphere window flow to the magma chamber, with corresponding flank fissure periods during record warm periods.

If the window aperture were relatively narrow, the adjacent plate flexure may explain sensitivity to continental isotactic shift and through changes in sea floor pressure.

Conjecture of course, but interesting correlations nonetheless. If this were true, it might provide a basis for modeling past events and predicting activity cycles as a function of climate and sea-level change.

I wouldn't exactly call that helical. A bend, yes... but I don't think a helix from that small amount of data. (2009 to like... two days ago)

I did see a helix pattern in some of the EyjafjallajÃ¶kull quakes, but I can't tell you what it means... other than being an interesting fracture pattern.

#19 Yes, I recall having seen that pattern elsewhere too, that's why I mentioned it. Maybe there isn't enough length for a full helix to develop, or maybe magma isn't fluid enough to let it go, but it looks like, for my amateur eyes, after so many plots of crust and mantle features, that there's always this twisted shape in most instances, whatever they be, faults, quakes or rising magma. Comes to my mind another discussion upon its vortex-like behavior. (??!!!)

That's the idea of the blog!
Learning more and more. I hope in the future an article of the different types of volcanic quakes (VT, LP, HB, etc.) to know what they mean, not only the abreviations, but the physical interpretation.

Boris,

Thanks Boris, I'm looking forward to part 3. I was on Etna in october 2009 and returned in july this year, I never realized that Etna is such a huge volcano. The pit at the foot of South-East crater was intermittently steaming vigorously. http://picasaweb.google.nl/ptibben/EtnaSicily#5507022110941199874

@Renato Rio, I did my master's project on Pantelleria last year. It is in an extensional setting despite the overall tectonics being compressional, which surprised me to begin with. GPS studies show that the western tip of Sicily is moving slightly more eastwards than Tunisia, leading to E-W stretching in the Sicily Channel. Paleomag also shows Sicily has rotated clockwise. Why this should be happening, though, I never did find out; I was measuring CO2 output so it wasn't really relevant. Boris may know more, he did write a paper on it, after all...

After the past week of non-stop earthquakes around the world this quiet trend that has been going on for the past few days almost feels like the calm before the storm.

Thanks again, Boris. You've given us such an amazing resource. Non-scientists almost never have access to graphics like these, with descriptions and analyses written in non-scientific English. I'll come back to this again and again.

@24 Haven't really noticed a quiet trend, then again haven't really paid attention. However I have noticed the sun's activity has quietened down from what is was the last few months. I'm not making any connections here just an observation.

@26 Chris, Did you see the solar eruption yesterday that happened on the far side of the sun, it was a blast which produced a C4-class solar flare and hurled a bright coronal mass ejection (CME) over the sun's western limb?

http://www.spaceweather.com/swpod2010/18aug10/cme_c2_512.gif?PHPSESSID=…

I look at the solar weather site too, it is possible that the magnetic storms could effect more that we think.

Thank you, Boris! My knowledge is by far not good enough to understand everything but I still very much enjoy reading your great texts! Keep it coming, please :-).

Renato 11/12: Thanks for these references. it looks like the western end of Sicily is as complicated as the east (and thanks for that to Gareth too) I wonder if the CFdMS activity has some relation to that curious kink in the plate margin down the west of Sicily (diagram from Boris' link to Highly Allocthonous) We really need Boris on this one.

An ability to visualise in three dimensions is vital for geologists..it's something I'll have to re-learn :o(

Gareth: more please sometime on Pantelleria, it's one of those forgotten volcanoes that no-one ever mentions

@Gareth:
Thank you for the update. It is becoming clearer now.
@Mike don:
Thanks for bringing up the question. It was a fascinating piece of research.

@23, Gareth: this citation answers your question on the clockwise rotation you mentioned in your comment.

Structural evidence for Neogene rotations in the eastern Sicilian fold and thrust belt. Monaco and DiGuidi (2006)
J Struct. Geol. 28(4):561-574.

>From a geodynamic point of view, the Neogene clockwise rotation in the eastern Sicily fold and thrust belt is related to the regional framework of the AfricaâEurope convergence.

Historical Etna flow diagram from Dr. Behncke's post draped on Google Earth (3D) with roadways enabled. 3 x vertical exaggeration.

http://i37.tinypic.com/8ygcvq.png

@27 R.Hurst Yes I saw that. Pretty cool stuff. Seeing the sun build up to some high activity for the last few months and now showing some low activity again is a bit of a let down, almost anticlimatic. I was hyped up over all the sun activity then I read about 3 X-class solar flares that were directed at earth in 2005, I think it was, and really had no adverse effects besides some nice aurora's further south. Also I'm waiting to see if we get more swarms at yellowstone in the dec/jan time frame.... sorry to diverge from the Etna topic at hand.

@33Chris, A great site to see a dozen pics of the real-time sun each with a different filter is

http://www.solarmonitor.org/index.php

I made a mistake posting the sun comment on the Etna topic, I was aiming for the summer thread #2, sorry everyone.

I really enjoy reading about Etna Boris, I brought up this page at home and my 14 year old son saw your write-up. On Discovery channel last month we watched a show on the most dangerous volcanoes in the world and Mt.Etna was featured, lets just say that he was very impressed, you are a great writer Boris.

Lurking, master of charts could you do on on the activity at VatnajÃ¶kull?

Hello.This post was really motivating, particularly because I was investigating for thoughts on this subject last week.

Amazing points. Going to want a bit of time to ponder the info=D

I image this could be diverse upon the written content? even so I nonetheless believe that it is usually suitable for nearly any form of topic subject matter, because it might continuously be fulfilling to determine a warm and delightful face or possibly listen a voice whilst initial landing.

Etna Week (Part 1) - Brief Anatomy of an Exceptional Volcano

eklemetti — Mon, 16 Aug 2010 03:58:11 +0000

Etna Week (Part 1) - Brief Anatomy of an Exceptional Volcano

Etna Week Part 1

Mount Etna - Brief Anatomy of an Exceptional Volcano
By guest blogger Dr. Boris Behncke.

Italy truly deserves to be called "the Cradle of Volcanology" - not only because it hosts virtually all existing types of volcanoes and volcanic rock compositions, and seven of its volcanoes have had confirmed eruptions during the historical period (i.e. the past approximately 2700 years), but also because the earliest surviving eyewitness account of an eruption was written in Italy, the first volcano observatory and the first geothermal power plant were built in Italy, and three volcanological terms denoting styles of eruptive activity - Strombolian, Plinian, and Vulcanian - have their origin in this country. The word "volcano" itself has its origin from the southernmost of the Aeolian Islands, in the Tyrrhenian Sea north of Sicily, Vulcano. Vesuvius, uncomfortably close to Naples and its very densely populated suburbs, is possibly still the most famous volcano worldwide, and certainly one of the most dangerous volcanoes on Earth.

Snow-covered Etna seen from the village of Trecastagni, on the southeast flank of the volcano, in January 2008, taken by Boris Behncke.

In this exceptionally varied volcanic setting, Mount Etna on the island of Sicily is a volcano of superlatives. It is the most active volcano of Europe and - after KÄ«lauea on Hawai'i - possibly the second most active volcano on Earth, in terms of eruption frequency and long-term average magma output rate. It has the longest record of documented eruptions of all volcanoes worldwide, and can be said to be virtually continuously active, with significant eruptive events occurring almost every year. Its summit stands at 3330 m elevation as of 2010 (Neri et al., 2008), making it the tallest mountain in the Mediterranean basin, and the highest summit in Italy to the south of the Alps. Besides the four nearly continuously active craters at its summit, Etna has approximately 350 craters and minor vents on its flanks, each of which erupts only once, and many of which form sizable cones, like miniature volcanoes, on the flanks of the mountain.

But what makes Etna really unique is its incredible versatility in terms of eruptive styles, eruption magnitudes, and eruption locations. During the historical period, it has produced numerous effusive, Hawaiian to Strombolian style eruptions from vents both at its summit and on its flanks, sometimes purely effusive activity going on for years, countless short-lived episodes of violent Strombolian to sub-Plinian fire fountaining accompanied by voluminous lava and tephra emission, Vulcanian and phreatomagmatic explosions and persistent ash emission sometimes lasting for months (Branca and Del Carlo, 2005). This record is punctuated by a Plinian eruption in 122 B.C. (Coltelli et al., 1998), which caused devastation and hardship to the population of Catania, a city that had been founded more than 600 years earlier by the Greek at the southern base of the volcano. Pyroclastic flows, the most lethal and destructive of all volcanic phenomena, have been observed on a number of occasions in recent years, but luckily affected only the remote summit area (Behncke, 2009).

In spite of its frequent and sometimes violent and hazardous activity, Etna has claimed a surprisingly small number of human victims - less than 80 deaths can be with certainty attributed to the activity of the volcano in the past 2700 years. This figure might be higher because the historical record contains several gaps up to a few hundred years long, like the Arab domination from the 9th to 11th centuries A.D. (all Arab records were lost during the Christian recolonization); yet it is clear that Etna is not a killer volcano, and this is one of the reasons why the people living on its slopes call it "the friendly volcano".

Geological setting and evolution of Etna
Like all things in Italy, the geodynamic setting of Etna is a bit complicated. For this reason, the origin of Etna has been ascribed by various workers to subduction, rifting, and a mantle plume, and more recently, some more exotic factors.

Sicily lies on the boundary between two converging (or colliding) lithospheric plates, the African plate to the south and the Eurasian plate to the north. This convergent margin runs across much of the Mediterranean along a general east-west trend, but shows a marked bend in Italy, where it turns NNW up to the Alps before taking on a SE trend in the Balkans toward Greece. Differently from many convergent plate margins, where one plate consists of oceanic and the other of continental lithosphere (like in the Pacific Northwest of the U.S. where the oceanic Pacific plate runs into, and dives underneath the continental North American plate), the colliding plate margins in Italy are heterogeneous, with bits of oceanic lithosphere alternating with continental lithosphere. The character of convergence therefore changes over short distances from subduction, as in the Calabrian and Aegean arcs, to mountain building as in northern Sicily and along the Apennines and the Alps.

The volcanoes of the Aeolian Islands are believed to be, at least in part, due to the subduction of oceanic lithosphere of the Ionian Sea under the Calabrian arc. However, rather than consistently erupting calc-alkaline magmas as subduction-related volcanoes commonly do, the Aeolian volcanoes also produce more sodium and potassium-rich magmas, which some scientists attribute to magma melting at different depths along a very steeply dipping subducting lithospheric slab (Tommasini et al., 1997).

While out in the Ionian Sea, to the east of Sicily, the northern margin of the African plate consists of oceanic lithosphere subducting underneath the Calabrian arc, on the island itself it is constituted by rather thick continental lithosphere, which makes up the southeast corner of Sicily. Rather than subducting, it bites and pushes into the continental lithosphere of the southern margin of the Eurasian plate. The result is mountain building - much like in the Himalayas or in the Rocky Mountains - going on in the Peloritani, Nebrodi, and Madonie mountain belts, which together constitute the northern backbone of Sicily. Etna lies just north of the plate boundary and away from the Calabrian arc subduction zone, in a rather uncommon place for a volcano to occur, plate tectonically speaking. For this reason, some researchers have invoked a hot spot origin of Etna, and of the older volcanic area of the Monti Iblei to the south, where volcanism has occurred over more than 200 million years (Schmincke et al., 1997; Tanguy et al., 1997; Behncke, 1999). Schiano et al. (2001) present arguments for a transition from a hot spot origin to a more and more pronounced subduction component in Etna's magmas. However, the hot spot model is not plausible because volcanism has shown a northward shift from the Monti Iblei to Etna, which would require movement of the African plate to the south, whereas in reality the contrary is the case (the African plate is moving northward).

Interpretative sketch of the geodynamic setting of Mount Etna, based on Gvirtzman and Nur (1999). From Armienti et al. (2004)

A series of recent publications (Gvirtzman and Nur, 1999; Doglioni et al., 2001; Schellart, 2010) places Etna into a context of slab rollback related to the subduction of Ionian oceanic lithosphere below the Calabrian arc. Slab rollback means that the bend where an oceanic plate starts descending into subduction moves gradually away from the subduction zone due to the weight of the subducting plate, and consequently it sort of tears the subduction zone and the overriding plate into the direction of the subducting plate. In the case of the Ionian plate subduction this would mean that the subduction zone migrates southeast, which is well illustrated here at Highly Allochthonous. This leads to the tearing open of a gap between the subduction setting of the Ionian oceanic lithosphere and the Calabrian arc to the east, and the continental collisional setting of Sicily to the west, which in turn causes decompression and the formation of magma in the upper mantle below this opening gap, or "window". The magma rises along the intersection of a number of major regional fault systems and feeds the activity of Etna.

Whatever the geodynamic cause of Etna, it appears to be highly efficient. Throughout its roughly half-million-years-long history, Etnean volcanism has become more and more vigorous and increasingly focused on a large volcanic edifice, eventually leading to the building of the large mountain that dominates Sicily today. The geological evolution of Etna is subdivided into four main phases: (1) the Basal Tholeiitic phase, (2) the Timpe phase, (3) the Valle del Bove centers phase, and (4) the stratovolcano phase.

Geological map of Mount Etna, from the INGV-Catania web site (courtesy of Stefano Branca). Key: (1) Recent alluvial deposits; (2) Mongibello (past 15,000 years) eruptive products (2a) "Chiancone" volcaniclastic debris deposit; (3) Ellittico eruptive products; (4) Valle del Bove centers eruptive products; (5) Timpe phase eruptive products; (6) Basal Tholeiites; (7) Sedimentary basement; "Faglia" = fault, "Orlo della Valle del Bove" = Valle del Bove rim; "Crateri Sommitali" = Summit craters

Distribution of eruptive products of the four main phases of volcanism in the Etna area: (a) Basal Tholeiites; (b) Timpe phase; (c) Valle del Bove eruptive centers; (d) Stratovolcano phase. From Branca et al. (2004)

(1) Basal Tholeiites. The first phase of volcanic activity in the Etnean area occurred about 500,000 years ago, in an area then occupied by a broad bay - referred to as the pre-Etnean gulf - leading to the emission of submarine lava (pillow lava) and associated debris, which is known as hyaloclastite. Some eruptive events lasted long enough to build small volcanic islands, much the same way as the island of Surtsey formed in 1963-1967 off the south coast of Iceland. Outcrops of these earliest products of Etnean volcanism occur along the coast of the Ionian sea immediately to the north of Catania, in the area of the fishing villages of Acicastello and Acitrezza. The castle rock of Acicastello is a world-class geological site (unfortunately not placed under protection as it would certainly deserve) where pillow lavas can be seen next to a typical breccia of small glassy fragments (hyaloclastite) and debris of shattered pillows (pillow breccia or flow-foot breccia).

The spectacular outcrop of Acicastello, on the coast of the Ionian Sea at the southeast base of Etna, where the earliest eruptive products of the volcano (Basal Tholeiites) are exposed. The left (western) part of the outcrop consists of densely packed pillow lavas, whereas breccias of shattered pillows and hyaloclastite (fragments of volcanic glass altered into yellowish-brown palagonite) make up the right portion of the section. Photos by Boris Behncke.

The products of this earliest phase of volcanism in the Etna area are tholeiitic basalts - virtually the same magma that is currently being erupted from KÄ«lauea (Hawai'i), which is the reason that this phase in the evolution of Etna is referred to as "Basal Tholeiites". Besides the outcrops of Acicastello and nearby locations such as Acitrezza and Ficarazzi, products of this phase occur also further to the west, near the town of Adrano at the southwest base of the volcano.

(2) Timpe phase. The second main phase of Etnean volcanism occurred between >220,000 years ago and about 110,000 years ago in a narrow belt along the Ionian coast along a fault system known as the "Timpe" (the steps). The Timpe faults are marked by conspicuous morphological scarps, and terminate to the NNW near Moscarello and Sant'Alfio on the east flank of Etna. During this phase, numerous fissure eruptions occurred in this relatively restricted elongate belt along the Ionian coast, and led to the growth of a NNW-SSE elongated shield volcano about 15 km long. The internal structure of this shield volcano is today exposed in the Timpe fault scarps between Acireale and Moscarello. During this eruptive period, sporadic volcanism also occurred along the valley of the Simeto river, constructing, amongst others, the large scoria cone that constitutes the hill of PaternÃ² and a number of thin, strongly eroded, lava flows like those cropping out in the northern periphery of Catania at Leucatia-Fasano. The products of this phase showed a shift from tholeiitic to alkali basaltic compositions.

(3) Valle del Bove eruptive centers. About 110,000 years ago, the focus of volcanism shifted from the Ionian coast into the area now occupied by the Valle del Bove. In this period, the character of Etna's activity underwent a profound change, from sporadic fissure eruptions as during the first two phases, to a more centralized activity of both effusive and explosive character. This activity led to the construction of the first composite volcanic edifices in the Etna region, the Rocche and Tarderia volcanoes. The products of these eruptive centers crop out along the base of the southern flank of the Valle del Bove at Tarderia and Monte Cicirello. Subsequently, the activity concentrated in the southeastern sector of the Valle del Bove, at Piano del Trifoglietto, where the main eruptive center of this phase was built up, Trifoglietto volcano, which reached a maximum elevation of about 2400 m. Three minor eruptive centers formed subsequently on the flanks of Trifoglietto, which are named Giannicola, Salifizio and Cuvigghiuni; their activity continued until about 60,000 years ago. This phase marks the formation of a stratovolcano structure in the Etna edifice and the superposition of different eruptive centers.

(4) Stratovolcano phase. About 60,000 years ago, a further shift in the focus of eruptive activity toward northwest marks the end of the Valle del Bove centers, and the start of the building of the largest eruptive center of Etna, now named Ellittico (the elliptical), which constitutes the main structure of the volcano. The Ellittico volcano produced intense effusive and explosive activity, constructing a large edifice, whose summit may have reached a height of 3600-3800 m. Numerous flank eruptions generated lava flows that reached the Simeto river valley to the west of Etna. About 25,000 years ago, the Alcantara river was deviated from its former valley closer to Etna (in correspondence with the towns of Linguaglossa and Piedimonte Etneo) into the present-day Alcantara valley (Branca, 2003). Much of the Ellittico lavas and pyroclastics are present in outcrops in the northern wall of the Valle del Bove.

The tan-colored clastic rocks in these photos are the pyroclastic-flow deposits emplaced during the climactic explosive eruptions at the end of the Ellittico stage of Mount Etna, about 15,000 years ago. These deposits occur in outcrops near the town of Biancavilla on the lower southwest flank of the volcano. Photos taken in August 2001 by Boris Behncke

The Ellittico stage ended about 15,000 years ago with a series of powerful explosive (Plinian) eruptions (Coltelli et al., 2000), which destroyed the summit of the volcano leaving a caldera about 4 km in diameter. Intense eruptive activity continued during the past 15,000 years, largely filling the Ellittico caldera, and building up a new summit cone. This current summit edifice is called Mongibello. About 9000 years ago, a portion of the upper east flank of Etna underwent gravitational collapse, generating a catastrophic landslide (the Milo debris avalanche), and forming the huge collapse depression of the Valle del Bove, which still today bites deeply into the eastern sector of the volcano (Calvari et al., 2004).

Aerial view of the Valle del Bove, a huge collapse depression formed by a massive sector collapse of Etna's eastern flank about 9000 years ago. Much of the depression has been filled by more recent lava flows; the original depth must have been significantly greater. This view is from the southeast, showing the summit craters in the upper center. Photo taken in August 2007 by Boris Behncke

Following the Valle del Bove sector collapse, remobilization of the debris avalanche deposit by alluvial processes led to the generation of a detritic-alluvional deposit, known as Chiancone, which crops out between Pozzillo and Riposto along the Ionian coast. This huge collapse of the eastern flank of the Mongibello edifice has exposed a large portion of the internal structure of both the Valle del Bove eruptive centers and of the Ellittico volcano, which crop out in the walls of the depression. The eruptive activity of the Mongibello is strongly controlled by structures of weakness in the volcanic edifice, where most intrusions occur along a number of main trends.

These predominant trends are characterized by three main rift zones, the Northeast, South and West rift zones. Although much of the activity of the Mongibello volcano is effusive, numerous strongly explosive events are known as well, mostly from the summit craters (Coltelli et al, 2000). The most powerful eruption of this eruptive phase occurred in historical time, in 122 B.C. (Coltelli et al., 1998). This eruption, which occurred from the summit of the volcano, produced a large volume of pyroclastics (ash and lapilli), which fell in a sector on the southeast flank of the volcano, causing heavy damage in the city of Catania.

(Part 2 to follow later this week.)

eklemetti Sun, 08/15/2010 - 23:58

Tags

Thanks, Boris Behnke, for this interesting and clear explanation of the Mt. Etna.
Bevor I came on this blog I didn't realise that here in Europe we have " real" volcanos und how interesting they are!
Looking forward to Part 2.

Hello Boris Behncke, thank you,this is great stuff, especially for this neophyte who has been training on the EyjafjallajÃ¶kull eruption! Lots of information clearly expressed and building on what we have already learned. Looking forward to the next installments.

Etna is ... huge.

I am amazed at how much detail has been gathered about the history of the volcano. But when you conciser the size, there is probably a lot of information to be found.

Great article.

Terrific write-up on Etna Boris! Thank you for bringing us "up-to-date" on current thoughts about the history and behaviour of la Etna!

Thanks folks - and there's quite a bit more to follow later this week!

In the meantime Sicily's geodynamics continue to be alive. This afternoon (16 August 2010) we had a magnitude 4.6 earthquake in the Aeolian Islands, the epicenter being near Vulcano island. There has been damage to buildings and infrastructures on Lipari, Vulcano, and Salina, landslides, and 7 people have been reportedly injured.

No way saying whether this earthquake is related to Vulcano, which last erupted 1888-1890.

Some more info at www.flickr.com/photos/etnaboris/

Approximate timing of Etna's eruptive phases appears to correspond to Northern Hemispheric IceAge mass changes.

See Temp Figs, Sediment Records (temps) and pattern of temperature and IceAge volume changes, section on Glacials and Interglacials.

http://en.wikipedia.org/wiki/Ice_Age

Of particular interest is the timing of 100KY climate cycles, at ~500KY, where benthic O-18 shows large fluctuations.

Expanded map showing the collision interface between African and Eurasian plates.

www.uwgb.edu/dutchs/GeolColBk/BW/AfricanPlateBW.gif

Thank you, Boris, for the interesting first installment of Etna info. Sounds to me as if Sicily and the surrounding area is just about as complex as Island. I am still trying to wrap my head around slap rollback. I think I have an understanding of it, but I am not sure so I will be reading that again to see if I can make sense out of it. From the interpretative sketch, it looks very complicated and the geo community is really not all that sure what is the cause of Etna's activity because it "isn't supposed to be there" sort of thing.

Thanks for posting a picture of the Valle de Bove because that has given me a perspective of what that area looks like and where the lava flows were going in 2006. That was the time my DH and I watched the Etna Treking cam for six hours! That was awesome.

I look forward to your next post to learn more. You know, I miss your reports that you used to do on you web site. So much has changed!

Yay.... I found data.

INGV Centro Nazionale Terremoti

cnt.rm.ingv.it/earthquakes_list.php?year=2010&month=12&ml_selection=0

Gathered all quakes from 2010 to present and plotted.

View north

http://i34.tinypic.com/29cx3ie.png

View East

http://i35.tinypic.com/x411sl.png

Note: This plot goes down to 600 km, which is about 20 times deeper than my Icelandic plots.

And a zoomed in perspective view. Colors adjusted to reflect shallower depth limits.

http://i37.tinypic.com/10xfz21.png

Boris, what (if any) significance is there about tholeiitic basalt being the first eruptive products of etna, changing to alkalic?

Does it imply more of a mantle component in the initial products?

Also, given the large amount of melt that rises through etna, has there been any thought about whether the area might be prone to hosting a shallow magma chamber? What leads to that sort of thing? Is it a more diffuse area where intrusions take place vs the established magma path to the surface that etna posesses?

Boris' website page on Etna References, per citations referenced in his Etna introductory material.

http://boris.vulcanoetna.it/ETNA_references_ac.html

Passerby (#11) rightly noted that there were no references in this first Etna bit - they will come with the third part (I placed them at the end of the whole thing I submitted to Erik). So with a few days of patience you'll also get the whole bunch of references (there are many recent ones included, which are not on my old "Etna references" page) ...

Stay tuned.

Meanwhile, we're getting the happy information that today afternoon's M 4.6 earthquake near Vulcano has, as it seems, not caused any injuries to people. However, it's the Big News tonight in Italy, though there's a tendency to downplay a little bit on the side of Lipari's administration, we're at the apex of the tourist season!

@Lurking [8-9]
I think you just got your coordinates wrapped around your head... ;)

This should be on East longitude, ie. increasing from left to right when viewing North, and a northward plot should show longitudes, while the eastward plot has lats growing from right to left.

(Yeah, me too: the same head all the year round...)

Funny thing: when I started typing this comment, the keyboard was Chinese - never happened before; English pops up rather often, but this was the first spontaneous Chinese pop-up.

It's possible. I generated two of them when I saw the issue, I may have linked the wrong one. I'll go check.

err....

"increasing from left to right"

Which one are you looking at? That's what I'm seeing. "View North" has the low numbers on the left (west)

The "View East" has north to the left (high numbers)

If you are seeing something different please let me know.

@Lurking -
Woops! My bad (partially); what you have are mixed longitude/latitude texts.

Thanks, Boris for an informative look at Etna and its effects on the area surrounding it. I only wish I had read this before when I went up to Etna in 2006 and saw the lava flow from the 2003(?) eruption. It looked like the beginning of a 4 lane asphalt highway leading down from the summit almost to Linguaglossa (one lucky town). I was in Acireale. I wish I had known about the geologic area of Acicastello. For anyone interested in volcanoes their impact on culture and history, Sicily is a great place to visit.

I'm a fan of the INGV webcams. When are they going to fix the Stromboli webcams? And would you explain the thermal imaging webcam and what that is supposed to be telling us. I understand the thermal webcam for Stromboli but not the one for Etna.

Fantastic article Boris I enjoyed reading it.
Now what are the chances of you resuming the updates to Italy's Volcano's???? An excellent site and I've had withdrawal symptoms since you stopped updating it.

Thanks for the article Boris. Its very interesting to read.
Have you ever considered writing your own blog about Etna and whats going on there? Something like the style of your Flickr Postings today. I think there would be interest for it.

@Kultsi, Askola, FI

Okay, now I see it. The labels are backwards.

I'm currently working on extracting terrain data for Etna/Sicily in order to get a better view. I'll be correcting those labels then... if I don't decide to lash out at the guy who coded this PoS Ladserf software package in Java. (It should not take this long to save a [expletive deleted] file).

Boris, thank you for the discussion chock full of wonderful nuggets about Etna. I have to admit, I'm still a beginner, and it will take me longer to fully appreciate your information. I'm adding it to my "to read after more study" file. ;-)

@Dr. Boris Behncke
Never thought it could be sooooo interesting and enlightening to go through your article, specially the geodynamics part. I got stuck, like Diane, around the "slap rollback", but for what I could understand, it provides a very reasonable explanation which is not "mantle-plume"-related. The idea of a "window" tearing that subducting slab is amazing. It's like "rifting" in the middle of a subduction boundary, if I got it right. And Lurking plots show deep focus earthquakes typical for subduction zones, which denies the "hotspot" version.
I've been to Italy many times and my friends always wanted to drag me to Sicily, and I declined it for other historical locations, but next time this won't happen. Thank you very much indeed!

#9 #13 @Lurking
I've noticed the shifted labels too. Your plots go N through all Italian volcanoes and seismic zones up to Firenze, I think. Which makes it very interesting, because you can "see" magma rising to Stromboli, Vesuvius, etc.

M 4.5 - SICILY, ITALY - 2010-08-16 12:54 UTC
http://www.emsc-csem.org/Earthquake/earthquake.php?id=184125#maps

#20 @parclair
I forgot to thank you for the amazing link on Lake Kivu's methane harvesting, on the other thread. Very good "mood-stimulating" effect to me.

Thanks, Boris, my wife went to Etna when she visited back in the 70's. Erupting then. Amazing system.
Would like to see it and Sicily sometime...

Okay... a redo. Been fighting and cursing the terrain extraction program most of the day.

This is a pretty wild view, not real pretty, but its all of Sicily with the quakes planted under it. Perspective view.

http://i36.tinypic.com/2lxayde.png

And these two are closer in views with the terrain of Etna plotted over top of it.

Copy paste these two. (the forum monster will get me if I make them into links)

i38.tinypic.com/smrpya.png

i36.tinypic.com/5k38ki.png

Caveat: If I have hosed up the lat-lon labels again, I'm going to go out back and kick something.

Re: #25
Hydrothermal vents rising from the same aesthenosphere source, under Sicily?

Mount EtnaâIblean volcanism caused by rollback-induced upper mantle upwelling around the Ionian slab edge: An alternative to the plume model. Schellart (2010) Geology.

http://geology.gsapubs.org/content/38/8/691.abstract

#25 @Lurking: You did it again! Latitudes are supposed to be between 36Âº and 38Âº and longitudes between 12Âº5 - 16 Âº. :)

Well, then prove that this one is wrong...

http://i35.tinypic.com/dximu1.png

Plan view.

The North-South and East West things are just right. Good job!
BTW what was that spoofing all about on the other thread?

Some one was using my moniker and posting stuff using it. I noticed that they put some URL in their sig. I didn't follow it since it's usually some advert when the Intruder Bots strike. A lot of times it's a script that wanders around to make random but believable posts to drum up traffic or customers.

It looks like Katla is starting to stir again this morning, it seems that the activity is going in waves starting on the North fault line and slowly moving South, it almost seems that the fault line has a pulse.

http://en.vedur.is/earthquakes-and-volcanism/earthquakes/

Wow.... Etna rocks...!!

As a Frenchman, I don't get too often my fix of active volcanism (or I would have to go to La RÃ©union, which would be interesting by the way ;), and I'm absolutely delighted to have such a volatile neighbor not too far away... (unless it does what Eyjaf did this spring and grounds every aircraft for two weeks..)

Kudos to Boris Behnke for such a master piece of information.... To everybody who run this blog, Keep on the good work!!

Now, for everything to go insanely cool, I would love to have it erupt.... Oh nothing big, just the pyrotechnics we all know and love, without disturbing anything nearby!

@RH #32... check the depths. All 1km. Nothing to remotely get excited about it!

Boris;

love these articles, but could we get access to higher resolution images, please

Thanks;
Robert Somerville

WOW! I am amazed at how much detail has been gathered about the history of the volcano. But when you conciser the size, there is probably a lot of information to be found.

A wonderfull articles you have written here, I know a little bit about Etna when I was a master degre student and visited Etna in 2001. I have seen one unexpected eruption then I was in Sommitali crater, dangerous but stronger than a real thriller. Therefore, after your explaination, I now understand some detail better than in 2001.

A advised man staleness skin a move of revenge without tantalising foolery

Could the developer of this site contact me a.s.a.p - I may be able to help you out.

Welcome to Etna Week!

eklemetti — Mon, 16 Aug 2010 03:57:12 +0000

Welcome to Etna Week!

Italy's Mt. Etna erupting in November 2006.

Well, I am currently off in the wilderness, but that doesn't mean that things aren't still hopping here at Eruptions. We are lucky to have Dr. Boris Behncke of the INGV Catania as that blogger and he brings us a three-part series on Mt. Etna on the island of Silicy. That means this week is Etna Week here on Eruptions, so for all of you chomping at the bit for more information on the Italian volcano, you are going to get it (and then some).

modern-day satellites who can watch that same summit from space.

I think you're all going to love this series, so I'll thank Boris now for his great work. Enjoy!

eklemetti Sun, 08/15/2010 - 23:57

Tags

@Erik @Boris
This blog is similar to soap operas in Brazil: once you see the first chapter you get addicted. You guys should be in the entertainment business.
Just coming back from work to my daily checking of volcanic news (all quiet over Iceland) and you give us Etna! And introducing it with the most fantastic picture.
Good grief!
I have papers to write, but I'll just get a snack and read through the main page.
Amazing blog! I'm so happy to be here.
Thank you!

Heh, better than Shark Week! on the Discovery Channel.

@Boris:
Congratulations for the beautiful family you have.
I saw the picture of your daughter (http://www.flickr.com/photos/etnaboris/) playing with sulfur on Etna's slope and I remember that when I was a kid my mom used an old Portuguese formula ("talco Granado") to sooth our skin rashes. It consists of a mix of talc and sulfur and happens to be an excellent antiseptic and deodorant, specially for parts of the body exposed to heavy sweating. The patent was bought by Johnson & Johnson, and I don't know if it is commercialized elsewhere. Still today I use it as a dry deodorant (it has a slight sulfur smell but it proves to be excellent for feet and armpits).
I must say I was happy to find out that Etna has a low lethality history (only 84 in historical registers), otherwise I would be worried for your family safety. But the landscape and the volcano itself are stunning , so I assume you people must have a a wonderful time living in the shade of Mama Etna.
Looking forward to more information on this amazing volcano.

GVP's Sally Kuhn Sennert answers your questions!

eklemetti — Fri, 13 Aug 2010 02:49:04 +0000

GVP's Sally Kuhn Sennert answers your questions!

Earlier this summer, we had a chance to ask Sally Kuhn Sennert of the Smithsonian Institution/USGS Global Volcanism Program questions about her job as the main writer of the well-loved Weekly Volcanic Activity Report. Well, now here are the answers!

Sally Kuhn Sennert of the Global Volcanism Program in front of Mt. Rainier, Washington.

Q&A Sally Kuhn Sennert:

Q: Could you describe how you go about putting together the weekly update?
A: If time permits, I would start to gather information on Friday when particular sources post their weekly summaries. The majority of the information gathering, however, actually happens on Monday mornings, when I visit about 40 websites. I also rely on reports coming to me via email either directly from the source (like from Rabaul Volcano Observatory) or indirectly through news feeds. I read the source information and write reports for most of Monday and Tuesday, often revisiting sites for updated information in the process. On Wednesday morning, I check a few more sites and then pass the "finished" Weekly Report to colleagues. The Report then goes through two rounds of editing by two of three regular Weekly Report editors in the Global Volcanism Program. In the meantime, I prepare the website files, such as the interactive map. If everything goes smoothly, the Report should be posted around 4 PM on any given Wednesday! Whew!

Q: How do you differentiate between reliable and unreliable sources?
A: I consider THE authority to be the folks at individual observatories and therefore the reports they produce. I also utilize the notices from the multiple Volcanic Ash Advisory Centers (VAACS). News reports are also important, especially when there are no other sources. With the media, I try to only use major sources, such as Reuters or Associated Press, and I use them carefully! Once in a while, one of the sources gets something wrong (analysts initially thought plume seen in satellite imagery was from volcano- later discovered it was from forest fire) or I misinterpret a translation, and a correction has to be posted in the report. That is the nature of the "rapid reporting" of the Weekly.

Q: Do you get a lot of "tips" from people about volcanic activity that is happening?
A: Funny thing about that- on a few occasions now, I have learned about eruptions I had no clue about from my grandma or mom!! In my defense, they are events that happened on weekends, when I am tuned out. Yeah, that's my story.

Q: What would make your job easier in terms of getting a complete picture of activity?
A: Definitely visiting more volcanoes!! It is so much easier getting the big picture of an event if you have been there and know the layout of the land or have seen the previous eruption products first hand. I would also love to meet more volcanologists (esp. folks at the observatories) around the world. Familiarity with people you communicate with is so important.

Q: How do you see the reports changing in the future? What about the GVP in general?
A: As the world becomes more digital, GVP has lost some of the personal connections with contacts that have really strengthened the monthly Bulletin, the database of activity, and to some degree the Weekly in the past. People used to call in or fax information, but now, observers can just post reports on their own blogs or websites! We are in the process of really reconnecting with people and fostering better information exchange. We are also continuing to improve our website and how we communicate to reach as many people as possible. For the Weekly specifically, I would love to see better maps available for each volcano- perhaps something 3-D and interactive.

Q: Have any new social networking sites like Facebook or Twitter made your job easier or harder?
A: Both! It is important to keep up with the current communication technology and methods; if you want to get your information out there, you have to do it in the way your audience prefers. The downside is that I can't keep up! My grandma and I share this complaint.

Q: What sort of questions do you get at the GVP from the general public? How about the media?
A: Public questions vary depending on the interests of the individual asking the question. GVP recently participated in the Smithsonian's Folk Life festival and showcased what we did. Questions from the public varied from why the "African Plate" is named the Nubia Plate to what was the magnitude of an earthquake that happened in the questioner's hometown on the day they were born. Questions like these, and seeing the wonder on people's faces when you talk about volcanoes or geology in any form, make it all worth it. Most of the questions from the media come during an eruption and center on trying to get us to predict when it will stop. Enthusiastic reporters are always fun to talk to, no matter what they try to make you say!

Q: Is there any way the general public can get involved with helping the GVP, the weekly reports or the website?
A: YES! GVP hosts several volunteers that work on the Bulletin reports, if you're interested drop me an email. We also welcome reports of volcanic activity from anyone that will send them, either volcanologists doing fieldwork or the casual vacationing observer. We do need specific information to incorporate the information into a report, such as date of observation or where the observer was. The more info the better! Many of our reports of volcanic activity "in the middle of nowhere" come from a recreational sailor passing by or a hiker on an adventure. I often ask, if a volcano in the ocean erupts and no one is there to see it happen, did it? A later random floating pumice raft may have the answer.

Q: What volcanic event of the last few years was the most interesting to follow?
A: The eruptions that stand out in my mind are from Jebel at Tair (2007), Nevado del Huila (2007), Kelut's dome growth (2007), ChaitÃ©n (2008), Sarychev Peak (2009), and finally the 2010 EyjafjallajÃ¶kull eruption. All of these events were new, exciting, important, and fun to follow.

Q: What else do you do for the Global Volcanism Program and/or the Smithsonian Institute/USGS?
A: My current high-priority "other project" is to write film scripts. I am helping my Global Volcanism Program colleagues create short educational films based on our historic film footage archive that we are currently digitizing. Several will be available on-line very soon, and in multiple languages.

Q: What is your favorite volcano?
A: I have to pick only one? That is tough! My default favorite (from grad school days) is PopocatÃ©petl, specifically because of the fabulous existence of "Popo Cam", but when I really think about it, I have to say Kilauea. It is such an interesting and accessible volcano! People from all walks of life, all ages, all backgrounds and interests can go there, hopefully at the right time, and have an experience of a lifetime. I lucked out when I participated in a field school and got to stand on cooled lava flows while watching (and feeling the heat of) new Earth being born right in front of me. I will never forget my time there, and probably never again eat a burrito as good as the one I cooked on an incandescent crack.

Q: How do you determine which volcanoes are listed in the active category versus the ongoing category (each week)? (From Diane; Stephen in the UK)
A: There is a page called "Criteria and Disclaimers" that discusses the topic of your question (http://www.volcano.si.edu/reports/usgs/index.cfm?content=disclaimers). Even though the reasoning behind the category assignment seems straight-forward, there are some volcanoes or some eruptions that don't quite fit the mold. So I sometimes consider the assignment on a case-by-case basis. For instance, I reported seismic swarms (no eruption) at Melimoyu in mid-June 2010. That volcano has never been reported on in the Weekly or the Bulletin, as it has only two documented eruptions in the Holocene. I assigned it to the "New Activity/Unrest" section to draw attention to it simply because it has not been reported on before. There are other volcanoes that have periodic or "typical" seismic swarms that I don't include in the weekly at all.

Q: Why are there sometimes unfinished or outdated information on the Global Volcanism Program website? (from Jon Friman)
A: The only area that may seem "unfinished" that I can think of is the Geologic Summaries written for each volcano. They are occasionally written in a way that does not accommodate new activity, and need to be re-worded. They, along with some other areas of the website, get updated yearly. As far as "outdated," one of the main goals of GVP is to database and archive information about volcanic activity over the last 10,000 years. We are currently archiving data from volcanoes active in the Miocene as well. So, by design the archived information is "outdated!"
Seriously, if you see something on the website that seems incorrect, unfinished, or just leaves you scratching your head, please email me and I will certainly look into it.

Q: Why was the recent large eruption at Redoubt 2008-2009 removed from the list of larger Holocene eruptions? (from Riggs)
A: I am not aware that it was there and removed. The list of large Holocene eruptions consists of volcanoes with VEI eruptions classified as 4 or higher. Perhaps the Redoubt eruption in question was thought to have been a 4 or higher at first and then changed to a 3 once the activity and products were better understood.

eklemetti Thu, 08/12/2010 - 22:49

Tags

Global Volcanism Program

Q&A

Smithsonian Institution

@Erik Klementti:
We are most honored to have Sally Kuhn Sennert answering to our questions. Hope she will continue doing her wonderful job and that we may someday be able to provide some contribution from here. And hope she comes back again.
Looking forward to see the new improvements to the GVP site. It will be great to have 3d maps and footages to illuminate our volcanic discussions.
Thank you Sally and Erik!

I've obviously missed the opportunity to forward a question and I would like to make up to that.

I would like to know why a continuous red status volcano like ChaitÃ«n is left out of the report.

Thanks in advance for answering my question and the opportunity to ask questions in the first place.

Great opportunity, continue the good work.

And maybe we should thank her for another recent improvement to the GVP site: a vastly increased photo archive for many of the world's volcanoes

I'd like to thank Sally and everyone at the GVP for the weekly report. I always look forward to Wednesday afternoons!

Also, to echo mike @ #3, the GVP recently added thousands of volcano photos to the site.

Keep up the good work!

OT: For everyone that could answer. A volcano classified as a 'caldera' could be a 'stratovolcano' at the same time?
Because I think there are stratovolcanoes that have a caldera only as a morphologic feature caused by an individual eruption.

For stratovolcanoes that have calderas as well look no further than two of the largest eruptions of the last two centuries: Tambora and Pinatubo. Both volcanoes now have a substantial caldera but both also retain enough of a peak to still be a stratovolcano as well.

OT, a new episodic tremore slip (ETS) initiated in the northwest a few days ago. These events happen every 14 months or so and it was only a few years ago that seismologists figured out how to tease the tremor signals out of the background noise. The tremor seems to be associated with non ductile shearing and/or hydaulic movements in or near the accreationary wedge above the subducting plate. To me this sounds like part of the story of the ongoing uplift of the eastern Olympic mountains, but I haven't yet found a report that identifies if there is a vertical component to the tremor.

Here are two site that track the episode:
the blog, with near daily comments and links to previous events: http://www.pnsn.org/WEBICORDER/DEEPTREM/summer2010.html

the data map, updated daily with tremor location: http://www.pnsn.org/tremor/

Thank you ,Sally for answering our questions. I check the info periodically and I plan to check it more regularly again as I used to. Thank you for the work you do.

@R. de Haan: The ChaitÃ©n status was lowered to yellow a few months ago, although is still moderately active.

Thank you, Sally Kuhn Sennert, for answering our questions. Come back and see us!

Riggs is actually the name of my beagle, as is Sassy, I used them in my email addy.

CHAITEN Southern Chile 2008Â Â MayÂ 2Â 4
OKMOK Aleutian Islands 2008Â Â JulÂ 12Â 4?
KASATOCHI Aleutian Islands 2008Â Â AugÂ 7Â 4
REDOUBT Southwestern Alaska 2009Â Â MarÂ 22Â 4
SARYCHEV PEAK Kuril Islands 2009Â Â JunÂ 11Â 4

http://www.volcano.si.edu/world/largeeruptions.cfm

I read your post very impressed seen this kind of important informationâs. Really am interested to back to your blog again to gather some more informationâs.

I'm Sally's grandma, and LOVED the article she wrote ! Talk about a proud grandma ! Way to go , Sally Sue ! You are special , and much loved !

Hi Sally,
What a wonderful article. I had no idea I had such a smart, talented great niece! Your field has to be very exciting and interesting. Keep up the good work!
Virginia Norris, Fla.

Wow, Sally, I am impressed with all you do. Of course, I don't understand much of it, but I'm impressed nonetheless.
I have such a smart niece!!

What a great article and interesting career you have! I am ERUPTING with envy!!!!

I have been here before but this is among the best blogposts yet. continue the good work!

Wednesday Whatzits: Mixing it up at Hood, alert lowered at Taal and plumes over Vanuatu

eklemetti — Wed, 04 Aug 2010 02:09:35 +0000

Wednesday Whatzits: Mixing it up at Hood, alert lowered at Taal and plumes over Vanuatu

Mt. Hood in Oregon, taken August 2008. Image by Erik Klemetti. Click on the image to see a larger version.

Quick news!

I'm not going to go into too much depth right now about the recent study published in Nature Geoscience on Mt. Hood in Oregon - I plan to talk about it more in a few weeks. Why is that? Well, the lead investigator on the study, Dr. Adam Kent of Oregon State University, is a friend of mine (and occasional Eruptions commenter) so I plan to get the details from him before posting. I was also peripherally associated with some of this work - mostly in the field acting as a pack mule and offering my witty observations. Nevertheless, the long-and-short is that magma mixing seems to be a strong control on eruptions at Mt. Hood, where mixing of two different magmas (one felsic, one mafic) can trigger an eruption. This mixing could be only weeks before the eruption, suggesting short time intervals between the trigger of an eruption and the eruption itself. Interestingly, Mt. Hood seems to play by its own rules in this respect relative to what we know about how other Cascade volcanoes behave.
Lava continues to flow from Kilauea into the area around Kalapana, although it has slowed. Only two breakouts were noted near Kalapana on August 1, suggesting that less lava is flowing. However, lava continues to reach the ocean to the southwest of Kalapana.
PHIVOLCS lowered the alert status at Taal to level one after signs of eruption waned, with only 5 earthquakes over the last 3 weeks. However, the restrictions for tourists remain in place for the time being as new measures are created, especially when it comes to approached the main crater. At the crater, steam explosions can still happen unexpectedly and the concentrations of volcanic gases can be dangerous.
The NASA Earth Observatory posted an image of the plumes from Ambrym and Gaua in Vanuatu. You can see the thin, wispy plumes of mostly steam and volcanic gases (which possibly some very minor ash) drifting to the northwest.

eklemetti Tue, 08/03/2010 - 22:09

So if there is an earthquake swarm at Mt Hood it would be best to take notice earlier rather than later.

Here is the abstract of an interesting paper. I wonder if the full paper gives any specific info on plate tectonic differences below Mt. Hood? (From mantleplumes.org)

Xue, Mei; Allen, R.M., Mantle structure beneath the western United States and its implications for convection processes, J. Geophys. Res., 115, No. B7, B07303, 2010.

@2: No, it's a 'Big Picture' type article. Better reads on the cold mantle down-welling process under Western US:

Dripping 'Blob' Under Western U.S.: A Hidden Drip, Drip, Drip Beneath Earth's Surface. Science Daily May 2009

www.sciencedaily.com/releases/2009/05/090526171813.htm

John D. West, Matthew J. Fouch, Jeffrey B. Roth, Linda T. Elkins-Tanton. Vertical mantle flow associated with a lithospheric drip beeath the Great Basin. Nature Geoscience 2, 439 - 444 (2009) DOI: 10.1038/ngeo526
(full paper below)
www.iris.edu/hq/esreg/priv/download_file/127

Western USA mantle structure and its implications for mantle convection processes. (same authors as paper cited by Pyromancer)

seismo.berkeley.edu/annual_report/ar07_08/node14.html

"Nevertheless, the long-and-short is that magma mixing seems to be a strong control on eruptions at Mt. Hood, where mixing of two different magmas (one felsic, one magma)"

I am assuming you meant one felsic, one mafic...or did you mean that a felsic magma can interact with any other type to trigger an eruption?

@VolcanoMan - Oops, thanks for catching that. It was supposed to say "mafic". Will fix it now.

TJÃRNES FZ:

I have been waiting for someone with a bit of knowledge to write about the long series of quakes we have been seeing at TFZ (about 10 km north of GrimsÃ¶y).
It has after all been going on for more then 2 weeks now without letting up.
The action is not situated at the site of the 1868 underwater eruption, it is to the nort-west to it. Lurking did a nice picture of it a week ago that seemed to show that it was a pipe pattern to the quakes.

So, anybody with a take on this? Is it an eruption, or a what?

Looking forward to any answer.

Hey that's an amazing insight on the subject, thanks so much! never heard it more clear.

A sense of humor... is needed armor. Joy in one's heart and some laughter on one's lips is a sign that the person down deep has a pretty good grasp of life.

Just texted my mom to see if she wanted to get pedis after work. It was only after I sent it that I realized iPhone corrected 'pedis' to 'penis'. I asked my mom if she wanted penis after work. Brilliant.

I hope that guy that "wants to be a billionaire" makes $999,999,999.00 and then gets hit by a bus

You must never promote a journey of revenge without giving a lunatic : Confucius

Things you mentioned made . Nevertheless, think about this, what happens if you offered a little more? I mean, I do not want to teach the way to write your site, but if you actually added something which can grab people's focus? Simply like a video or a graphic or few for getting viewers psyched about what you are talking about.

Very useful article. Myself and my neighbor were getting ready to do a little study regarding that. We bought a helpful guide on that issue by our own neighborhood library and many publications are not as descriptive as your content. I am very thankful to discover such info which I was searching for a long time.

A volcanic cruise through the Mariana Islands: Part 2

eklemetti — Fri, 16 Jul 2010 05:43:30 +0000

A volcanic cruise through the Mariana Islands: Part 2

Our tour of the Marianas begins SW of Guam. In this area the volcanoes are submerged and make up a region known as the Southern Seamount Province. Our first stop is Tracey Seamount, which lies 30 km west of Guam. Tracey is a ~2 km tall cone and volume of ~45 km³ It is one of the smaller volcanoes in the Mariana arc; Pagan, contains about 2200 km³ of material (Bloomer et al., 1989). It has a sector collapse on its western flank and resembles a submarine Mt. St. Helens. It was investigated by the ROV Hyper-Dolphin from the R/V Natsushima in Feb. 2009, which revealed that the cone is map up of alternating pyroclastics and dacite built on a basaltic-andesite base. A dome of dacite has formed in the collapse area. It is still considered active and that along with its proximity to Guam and its history of sector collapse suggest an underappreciated risk to the island.

Map of the volcanoes of the Marianas Islands.

Next up is West Rota. This is a large submarine caldera 40 km WNW of Rota. In fact it is the largest caldera in the IBM system, similar in size to Crater Lake in Oregon. Found in the caldera are large balls of rhyolite that are inferred to be rhyolite "balloons" that may have actually floated for a time after erupting (Stern et al. 2008). The youngest material dated so far is 37,000 years old, but there is evidence of current hydrothermal activity.

64 km of Rota and west of the main arc is the small but notable submarine volcano NW Rota 1. It is notable for being the site of the first directly observed deep submarine eruption. In 2001 it was dredged (my first cruise), but nothing unusual was noticed. In 2003 NOAA scientists detected an acidic plume above the summit. Subsequent dives by ROVs in 2004, 2005, 2006 and 2009 found continued vigorous activity, including sulfur-rich plumes, occasional small explosions and density flows of tephra down the flanks. The material being erupted is basaltic-andesite and despite the non-stop activity, no evidence has ever been observed on the surface that anything is going on down below. NW Rota is also the home to a rich ecosystem of shrimp and other organisms that are dependent on sulfur-loving colonies of chemosynthetic bacteria.

Further to the north we enter the Central Island Province, but not all volcanoes here have breached the surface. In addition to a multitude of small submarinevolcanoes, there are several larger ones: Esmeralda Bank, Zealandia Bank, Ruby and East Diamante Seamount. Several of these have some historic record of possible activity (mostly disturbed, discolored water) and Diamante has noticeable hydrothermal activity.

The islands proper start (moving S to N) with the intriguing Anatahan, which consist of overlapping calderas

Morning view of Anatahan from my room, R/V Natsushima June 2009.

Anatahan had a significant eruption in 2003 and there is an interesting story about Japanese holdouts on the island at the end of WWII that was made into little-known movie.

Sarigan is next.

Sarigan Island in the Marianas.

Recently there was a submarine eruption south of Sarigan. A cruise underway at this moment may, if time permits, send an ROV to visit the presumed eruption site.

Guguan last erupted in the 19th century. Alamagan to the north has no definitive historic record of activity, although there was a false alarm in 1999. Pagan is one of the few islands (outside of the larger Saipan, Tinian, Rota and Guam) to have any population. Even minor activity there presents a concern due to this. Agrigan has a caldera that was the site of small eruption around 1917. The symmetrical cone of Ascuncion had reported activity early in the 20the century, but its northern neighbors, the Maug Islands, have no historic eruptions and are in fact the eroding remnants of a caldera. Further north we enter another seamount province, except for Uracas or Farallon de Pajaros. This particular volcano and its submarine neighbors seem to be particularly restless. North of FdP is considered to be the end of the Marianas and the start of the Bonin or Volcano Islands.

Guguan and Alamagan Islands in the Marianas. Image by Ed Kohut.

References
Bloomer, S. H., Stern, R. J., and Smoot, N. C. "Physical Volcanology of the Submarine Mariana and Volcano Arcs." Bull. Volcanology, 51, 210-224, 1989.

Gill, J., Klemperer, S., Stern, R., Tamura, Y., and Wiens, D. 2003. 'Subduction-Factory' Meeting Studies Izu-Bonin-Mariana Margin. Eos, v. 84, No. 1, p. 3

Stern, R.J., Fouch, M.J., and Klemperer, S., 2003. "An Overview of the Izu-Bonin-Mariana Subduction Factory" in J. Eiler and M. Hirschmann (eds.) Inside the Subduction Factory, Geophysical Monograph 138, American Geophysical Union, 175-222.

Stern, R.J., Tamura, Y., Embley, R.W., Ishizuku, O., Merle, S., Basu, N.K., Kawabata, H., and Bloomer, S.H., 2008. Evolution of West Rota Volcano, an extinct submarine volcano in the Southern Mariana Arc: Evidence from sea floor morphology, remotely operated vehicle observations and ⁴⁰Ar/³⁹Ar Geochronology. The Island Arc 17, 70-89.

eklemetti Fri, 07/16/2010 - 01:43

Thank you again, doc Ed!

A question, though: at what depths are these submarine volcanoes, and how does that affect the ejecta, or does it?

Agrigan (Agrihan to the natives) had VEI 4 eruption in 1917, according to SI-GVP.

I'm also going to question the cited population (Wikipage) of less than 10 in 2006. No reason to believe that the island has become depopulated since this casual report was written in 1992. The officially reported by the US Census Bureau as zero in 2000 and estimated to be less than 10 in 2005.

The island had been continuously inhabited for 48 years at the time the author visited. Family members who go onto high school return to the island later on. The Chamorro indigenous people are nearly all Roman Catholic and tend to have large families.

My guess is that CMNI is reluctant to officially recognize settlers who haven't been granted land ownership - political shenanigans.

cnminorthernislands.com/current_doc/agrihan.html

I doubt that the CMNI authorities would be over-happy about having to evacuate ten unofficial settlers on Agrigan/Agrihan in the event of volcanic unrest there. Not impossible, since they have had to evacuate two islands (Pagan and Anatahan) in the last thirty years, and Pagan gave the authorities, I rather suspect, a nasty scare -warning earthquakes were ignored, and the islanders were only evacuated AFTER the climactic explosion

A couple of questions for EKoh:
West Rota - if both plates in the Marianas are oceanic crust (no continental material) where did the large-volume rhyolite come from?
NW Rota 1 - if it is west of, ie behind, the main arc, are its products more alkaline than the main arc volcanoes?

There was NO 'nasty explosion'. There was some EQ activity that raised alarms, which is apparently not uncommon nor are volcanic exhalations, according to that article which is dated two years after the incident. An unknown number lived on the island before the 1990 evacuation and they all apparently returned and were slowly increasing in number as of 1992.

My bad, the islanders are Carolinians (people originating the Caroline Islands, 2 different atolls speaking different dialects who migrated for work in the 1880s) and at about 6,000 total in CMNI, are a small non-indigenous Micronesian population.

en.wikipedia.org/wiki/Caroline_islands
www.pacificworlds.com/cnmi/arrival/comeash.cfm

USFWS biologists are conducting survey work in the islands this summer, so we can find out through the science grapevine.

Bill Chadwick might be able to answer your question on the lavas at NW Rota-1, although I think he might be on the field expedition Ed mentioned.

nwrota2009.blogspot.com/

Ed will have to explain the details of this paper, it's complex.

Evolution of West Rota Volcano, an extinct submarine volcano in the southern Mariana Arc. Stern et al. (2008)
Island Arc 17:70â89.
http://www.utdallas.edu/~rjstern/pdfs/W.Rota.TIA08.pdf.

OT: June 2010 SciAm has an article about postperovskite. A denser form of perovskite that may account for the seismic seen at 2,600 km.

Really OT [@Passerby]:

"...My bad, the islanders are Carolinians (people originating the Caroline Islands, 2 different atolls speaking different dialects who migrated for work in the 1880s)..."

I'm glad you clarified that, for a moment I thought that there might be an Algonquian link.

Re: boo boo

Please insert "discontinuity" between "seismic" and "seen" in my last post.

I'll have time later this evening to answer your questions on NW-Rota. Passerby, Bill Chadwick is usually not on the JAMSTEC cruises, but I think Bob Embley is supposed to be. I'll see if I can get any updates from them regarding NW-Rota activity.

Ed Kohut

Right, Bill wasn't on the JAMSTEC mission (Japan Agency for Marine-Earth Science and Technology), he was on the 2010 ROTA-NW expedition/NSF Vents Program at Sea, with the Jason ROV, and he was on the 2009 cruise as well:

nwrota2010.blogspot.com/2010/03/science-team.html
www.jamstec.go.jp/e/about/index.html

This large research group is part of longterm NSF program/project series to monitor and study the volcanology, chemistry and ecology of submarine vent systems.

The 2009 and 2010 expedition blogs are very cool to browse - and timely, with respect to Ed's series on Mariana Island Arc volcanism this week, but it's not the same expedition that Ed references in his post.

Sorry for the loon question.

What amount of stress does a subducting plate feel if "slab pull" is the main driving mechanism? Wouldn't there be a region somewhat away from the trench that experiences quakes related to the bending stress? Natch, it's actually a shallow bend towards the area of the trench, but is there a scenario where a segment could snap and create a new volcanically active region if not a full on large igneous province?

If it's too weird of a question, no biggie, I've been drinking.

The NW-Rota lavas are not that much different than typical Mariana Arc basalts in terms of alkalis. Within oceanic crust, the initial melts in spreading centers and the waning ones in hotspots tend to be more alkaline.
The Marianas arc is building continental crust, but the arc crust at this time is still relatively thin compared to Japan or New Zealand.
For the West Rota rhyolite, Stern et al. suggest that a basaltic magma provided heat to melt andesitic crust. Rhyolite is bery viscous and has difficulty reaching the surface in many arc volcanoes, but they suggest that the faults in the area provided pathways to the surface.
@9 Lurking, not a loon question at all. The slab pull and overall plate convergence create tremendous compressive stress in both the subducting and overriding plate, particularly in the forearc region. This stress creates thrust faults and they can build up a lot of strain or potential energy in between slips. When they go you can megathrust quakes with Magnitudes >9 and simultaneous uplift and subsidence on the coast and seafloor. This can produce tsunami. The 1960 Chile quake/tsunami, 1964 Alaska quake/tsunamiand the 2004 Indonesian quake/tsunami were all megathrust quakes. Just another reason why subduction zones are so important to understand.

Passerby 4: was that comment for me? I never mentioned a 'nasty explosion' -I said that the authorities were given a 'nasty scare' by the Pagan 1981 event. not quite the same thing, and a reasonable inference from the GVP 'Monthly Reports' for Pagan at the time. Nor did I say that the evacuation from Pagan in 1981 was permanent (because I have no information on that point) merely that, according to GVP, it took place

Passerby 8: Thanks for the links to the Rota blogs, they're going to be useful.

Ekoh: thanks for answering my queries about Rota rhyolite and the NW Rota basaltic andesites: on the latter, I asked because in other arcs volcanoes behind the volcanic front (eg Bogoslof and Batu Tara) are distinctively more alkaline, and was wondering if NWR-1 fell into that category. Obviously it doesn't.

The GVP monthly report was ambiguous on details of the evacuation. Certainly, Pagan was evacuated. Alamagan may also have been evacuated, but I can't find mention of Agrihan being evacuated in 1981, although we know it was populated at the time. Indeed, the extensive ash plume is described as traveling SSE, while Agrihan lies to the N of Pagan.

The subject was Agrihan, it's residents and the disjoint figures reported for it's population at various dates. I made no mention of Pagan.

Interesting things are happening in the Mariana Islands.

A new naval training base is under construction
www.saipantribune.com/newsstory.aspx?cat=1&newsID=101400

and increased military presence has spurred interest in seismic detection in the islands, with the USGS and it's prime collaborator, SMU, planning to install and operate 4 (probably more later) multi-sensor field sites:

Volcano monitoring will target threats to Marianas. Feb 2010
www.saipantribune.com/newsstory.aspx?cat=1&newsID=97566

which is a Very Good Idea, given the uptick in volcanic activity in island and submarine volcanoes.

See: Table of recent eruptive activity at Northern Mariana volcanoes.

Interagency Operating Plan for Volcanic Ash Hazards to Aviation in the Pacific Region of the N Mariana Islands. June 2009 (updated Aug 09)

www.ofcm.gov/p35-nvaopa/regional_plans/Draft%20Framework%20MARIANAS%20P…

Sorry for the misunderstanding; I thought you were casting aspersions (as painful as a bash on the head from a lump of scoria)

Guess the main hazard on Guam would be tsunami, either earthquake-triggered or as the result of edifice collapse since many Marianas volcanoes are pretty 'high' mountains with respect to their base, even if only the summits (sometimes) appear above sea level. I don't know much about the geography of Guam, but isn't it fairly low-lying? Ash hazard for aircraft, of course, but not such a problem for subs, I would think

USDOD keeps it future plans on the QT, but with increasing tension between the US and Japan over pollution, noise and crowding issues on Okinawa, the general impression is that 'some' US military base operations in Japan are going to shift southward to Guam.

Submarine training ops in Guam is the US answer to increasing Chinese Naval military exercises in the Yellow Sea.

However, the primary concern is surveillance and routine USAF ops hazards from volcanic dust in the region; hence it's presence in the cooperative interagency agreement I cited, wherein they supply met capabilities for plume and storm monitoring.

Meanwhile, Ralph at The Volcanism Blog has posted on a Volcano Art exhibition. Worth a gander.

volcanism.wordpress.com/

Science and the movies - I love it!

At one point, wasn't there a Northern Marianas Volcano Observatory? I haven't seen that for a while, but one can still get updates of the Northern Marianas volcanoes at http://volcanoes.usgs.gov/nmi/activity/index.php

Note that Pagan is currently at Yellow alert. The GVP eruptive history page doesn't have an stop date listed for the eruption that began on April 15, 2009, so perhaps this current unrest there is still considered a part of that eruption?

You're thinking of the USGS NMI webpage:

volcanoes.usgs.gov/nmi/activity/

And yes, according the update posted by the USGS duty officer for NMI (out of HVO), activity is ongoing at Pagan, but at low levels...for now.

The webpage will be expanded when the expanded monitoring system comes online.

Sooner would be better.

Off topic, but there was a 3.5 at Long Valley just an hour ago. Not very large but bigger than what's been going on the past few months, located inside the caldera rim.

Jen, I saw that. It seems a bit unusual as we haven't seen one of that magnitude for some time. I'll be watching that area as I usually check it every day.

On the open thread, I posted the info on two quakes on New Britian Is. One was 6.9 and the other was 6.8.

New Britain area EQ was upgraded to a 7.3 (occurred at 13:35 UTC)

Passerby, I just saw that. I was checking out other things and checked again. I don't think I would want to be there right now.

Dr. K,

An OT; do think the quakes on New Britian will have any affect on Rabal? I know that they can affect a volcano, but that doesn't mean they will. I just would like to hear your opinion.

Any opinions on the Alaska quakes? Relativly close to Cleveland and really strong...

@ Diane, don't forget all the other major volcanoes on New Britain, Dakataua for instance (http://www.volcano.si.edu/world/volcano.cfm?vnum=0502-04=), that are much closer to the epicenters and worth a look at (that said these quakes are tectonic thrust events and don't seem to be related to volcanism).

Bruce: I recall reading of some research -in that general part of the world- where the authors suggested a correlation between major earthquakes at depth and subsequent eruptions..but even if that applied in this case, and I'm not sure it does, for the same reasons as you, the interval between the two events was on a timescale of many months. I'll have to look it up..it's in my "library" (two shelves!)....somewhere

Mike, sounds tantalizing!! The region has certainly been extremely active. BTW, I've since realized Pago is much closer to the epicenters than Dakataua. Both of these volcanoes have had VEI 6 eruptions in the Holocene and are more or less in direct line with the epicenters of these quakes. I wonder how far down the plate boundary the rupture extended. The epicenter of the M7.3 event was at 53 km depth. As a rough guess the plate boundary is probably about 100 km under Pago which lies 40 km to the north of the epicenter.

To put it really crudely; even if the rupture extended down the boundary to underneath Pago this does not translate into the sudden provision of new melt even though of course the constant subduction of the plate releases a steady supply of volatiles. I guess that a much more critical relationship between large tectonic earthquakes and volcanic activity lies in the mechanics of the conduit and any magma chambers closer to the surface (though I now prefer the term mushy reservoirs after all I learnt about Eyjaf!!), i.e. local faulting and stress relationships in response to the tectonic movement could facilitate or thwart eruptive activity, which I guess is stating the obvious ... sorry for the long rant going nowhere ;-)

pardon, misusing terms. I meant hypocenter and not epicenter.

The pictures of Anatahan or Guguan would have been great "mystery volcano photos" :)

The European-Mediterranean Seismological Center reported a 6+ earthquake on Russian coast that happened approximately 9 hours ago and was not even mentioned by USGS. How come?

2010-07-18 13:42:35.8 (9hr 22min ago)
49.12 N 139.72 E 33 km6.0 (MAG) KHABAROVSKIY KRAY, RUSSIA

http://www.emsc-csem.org/#2

@Renato Rio [27]

Probably the same reason that many SIL reported quakes, even the 3+ ones, don't make it in there. It's also the reason that I can't make any definitive statements about some of the stuff I plot. I don't know the rhyme or reason for the different data sets.

Not everyone plays with the same deck of cards.

Re: www.emsc-csem.org

What a novel idea. "Export to CSV" generates a semicolon separated file. Gee, whoda thunk.

At least it generates an exportable file of some sort, most sites don't even do that.

Bruce #22, just checked a better map and the quakes on New Britian are a bit far from Rabal. I am not familiar with the other volcanoes on the island. Need to do some studying. :-) I know the quake was techtonic/thrust, though if it was strong enough and close enough, I would think it could set off an eruption if one was ready to start or close to it.

I am not too saavy on the relationship of the depth of the quake and the plate boundary. They were on the island just a few kms from the shoreline (or so it appears) and how far from the plate boundary is that part of the island not only horizontally, but vertically as well? I am curious.

#30 @Diane For what I 've been reading from past eruptions, I think there's enough reason for concern here, even though the EQ's have a tectonic origin and are not right under the caldera itself. There are two active vents involved (Wikipedia): Tavurvur and Vulcan which had two destructive eruptions in a recent past, just after similar EQs. This is the humble opinion of a non expert. :)

Overlapping coordinated networks have regional 'authorities and their partners' that specialize in monitoring and reporting for that region.

Map of the USGS Global Monitoring Network (US consortium)
earthquake.usgs.gov/monitoring/gsn/

The Big Picture is handled through many centralized data collection and notification systems.

An example list, but not comprehensive:
fullspectralimaging.net/edms.aspx

The Global Disaster Alert and Coordination System is one of the best known. GDACS employs JCS, the Asgard automated event collection and dissemination netork.
http://www.gdacs.org/sources.asp

You can subscribe to and received RSS alerts for any of the EQ reporting agencies.

IDEO was a failed attempt; it was meant to monitor seismic signals for the Atmospheric Test Ban Treaty.
www.ldeo.columbia.edu/~richards/EARTHmat.html

The US backed out of ratification. The NSF, however, had already started on it own Global Seismic Network under Neal Lane in the 90s and would be integrated into the USGS seismic system under the IRIS program:

http://geophysics.ou.edu/solid_earth/readings/global_seismograph_networ…

and by 2008 had exceeded it's original goals
geophysics.ou.edu/solid_earth/readings/global_seismograph_network.html

2009 report on the NSF GSN
adsabs.harvard.edu/abs/2009AGUFM.U51C0021B

Meanwhile, in the 90s, WHOI embarked on an ambitious project to build large seafloor seismic monitoring networks:
www.whoi.edu/oceanus/viewArticle.do?id=2388

to fill the gap in the global sesimic monitoring of the open oceans and coastal environments. We're talked about this program here, but it was some time ago.

USGS has sparse station coverage for Europe, by necessity.

@20 Diane,
Local tectonic quakes would probably not have affect on an eruption, unless things were ready to go. Very large quake, like the 1960 Chile quake redistribute a lot of strain over large area. Although that may not immediately cause an eruption, it has been suggested that it could affect magma deeper in the system. Boris or someone else who works on eruption mechanisms would have a better handle on it.

@26. I actually gave Erik a picture I took of Sarigan a while back and some one identified it right off the bat!

Ed Kohut

@Passerby

Thanks for the info. I just marked it up as a conspiracy. See, at only 33km deep, it's obviously evidence of the ongoing secret nuke test program disguised to look like a deep seismic event. Granted, 108,267 feet is deeper than the current drilling record... and the ambient temperature is conservatively in the 2012Â°F (1100Â°C) range just from the average gradient...

[Note to all, I'm joking]

Back to Passerby, I'm not joking about the usefulness of your data. I had always been puzzled about that. Thanks again.

#33 @EKoh Thanks a lot for your precious intervention. What I was trying to say about these volcanoes is that, to me, they look pretty much "ready to go". But this is mere speculation.

@Passerby: Thank you very much for the links . I didn't have any idea that there were different coverages on EQs. Not for a 6.0. Very useful explanation, indeed.

@Lurking: If that's the case, I'm curious: who would be running the nuclear program? The Chinese or the Russians? There was a big one in Taiwan a little earlier. Could that explain? ;)

There are fairly frequent explosions happening on the Sakurajima webcam right now if anyone is interested. You need to be a little patient to see the flying bombs and ash plumes but the camera often zooms in for some great closeups.

motsfo, are you still reading this? The weather's cleared enough around Redoubt to see it. It's still steaming? Has it been steaming since the eruption stopped? I'm thinking that if it's taking this long to cool down, Eyjaf will be steaming for quite a while.

(you have a) Curious sense of humor, Lurking (did I detect a touch of Raving's cynicism there?).

LDEO is still running, but at a more modest scale. The monitoring group has annual meeting and published proceedings, and updates.

www.ldeo.columbia.edu/res/pi/Monitoring/

Fortuitous use of CNTB treaty monitoring data includes large industrial explosion and major mining accident forensic investigations.

Happy to provide useful links that provides a bit of background / clarification on various topics here.

Just as a side note the thoro cam is especially perfect right now...clear good resolution and a nice white plume

Do you happen to know if the seismic network that did the preliminary intercept on the Kurst mishap was plugged into that info share? I thought that was one of the sharper collateral uses of technology at the time. Before that all I had read about was the use of SOSUS data to track whales and eruptions.

As an aside, recently there was a news report that the mine investigators were still having trouble at the VA mine disaster, and back on the 16th, there was a Mag 3.6. Nothing freaky until you realize that that's pretty much the same mountain range and that it's still experiencing quite a bit of stress... squeezing the rocks. The day before the mine incident there had been a quake about 45 to 60 miles north of the mine. Not that it caused it, but it demonstrated that the rocks were under stress. My guess is that this enhanced the movement of gases in the rock structures.

As for Raving's cynicism. I have my own people to doubt and axes to grind. None of them reside on this blog. On one hand, I'm hoping for a light schedule next week so I can play with more plots, on the other, I never turn down work. Even if it's driving 240 miles round trip to change a 2 cent fuse. I was a bit shocked at that one.

@EKoh

Thank you for your informative posts.

You mentioned that Pagan has sector collapse but that it reside underwater. Are the mechanics of that pretty much the same as the St. Helens event? I would think that the density of the water / buoyancy would impart different critical angles (angle of repose) for the slope, but I may be wrong.

@ Diane, you and me are in the same boat here, trying to understand the interaction between seismic events and local volcanoes. The things I learnt this week (thanks EKoh!) were that the volcanic front tends to occur along the line marked out by where the subducting slab reaches a depth of somewhere between 80 to 120 km, so you can pretty well assume that the plate boundary has reached this depth where you see a line of volcanoes. If you couple this knowledge with the charts of historic seismicity from USGS you can get a rough handle on the plate boundary.

BTW, I don't know if you've discovered this page on slab models at USGS. It's fantastic:
http://earthquake.usgs.gov/research/data/slab/

And if you want some juicy research into imaging plate boundaries in terms of their relevance for volcanism this work on New Zealand got me really excited a few years ago (check out the pdfs for excellent summaries)
http://www.gns.cri.nz/research/tectonics/subduction.html

@Passerby

##$@@$%... you point at some of the most distracting stuff.

While poking around the www.ldeo.columbia.edu site, I ran across a link to NE US events from March 2009 till July 2010. Well, I had to plot them. Interesting plot. And, it has a quake stack. I never expected to find one in the NE US.

i28.tinypic.com/25hzhhz.png

Slewing up to an overhead view, it appears to be next to Albany NY.

i30.tinypic.com/2s01g1w.png

Not having an explanation... I dug around for some sort of clue. A Magnetic Anomaly chart of that region. (derived from overlaying a segment of pubs.usgs.gov/sm/mag_map/mag_s.pdf on Google Earth)

You can see the Ramapo fault arcing up through New Jersey, but it's not on that structure, so I don't know what it is. This whole region is a collection of squashed volcanic arcs/islands that have been accreted onto North America, uplifted, eroded, shaved off rifted, glaciated.... you name it. Why there would be a near vertical quake stack there is beyond me.

On Google Earth, it's a gentle valley next to a hill. Maybe with a cow or two hanging out for good measure.

Anyone have any ideas?

Err, forgot the link to the Mag Anomaly map.

http://i32.tinypic.com/33c7mgz.png

@Lurking:
It is amazing how much quakes a large mine can produce.
Since I live "close" (relatively speaking) to the worlds 2 largest pit-mines I have a fair knowledge about the level of seismic events they produce.

The Kirunavaara mine regularly produces quakes between 1 and 3,5. The principles on mountain stress is fairly well known. The only thing people are waiting for now is when they will have to let the former mountain rest.
With a new 1300+ meter level in the making it will sooner or later become interesting times. As you all of course know the mountain stress increases with depth of the mine. And pretty much it is unknown territory since no one has ever operated a mine at that depth and with the enormous speed of iron ore blasted out of the ground from that depth.

http://sv.wikipedia.org/wiki/Kirunavaara

www.lkab.com

@Carl, Mining

What sort of geological event caused such a large high concentration of iron ore? In the wilds of Russia's mining region are the Siberian Traps, and in a sector of Canada rich in copper, there was an impact event whose crater melt concentrated the ore. Was this just mountain building?

@41:
Hunting Hilltowns earthquakes (April 29, 2010)
www.timesunion.com/ASPStories/story.asp?StoryID=926208

Seismologists studying this activity are from LDEO
(Columbia University's Lamont Doherty Earth Observatory)

The article says: local fault system that originates near Lake George.

Geology of the Lake George/Adirondaks
www.lakegeorgeassociation.org/html/geology.htm

Do not know if LDEO was plugged into the 2000 Kursk OSCAR-2 submarine disaster investigation, but presume so indirectly, as the initial explosion caused ~6-7 torpedo warheads to ignite, causing the fatal secondary ruptures that sank the vessel.

@Lurking #47 http://epubl.luth.se/1404-5494/2005/46/LTU-HIP-EX-0546-SE.pdf gives the following explanation (2.1 Geology):

The ferro-apatite iron ore body is about 1,900 million years old and the area is part of the Sveco-Karelian Orogen Complex. The body, some 4km long by 80-90 m width on average and more than 1Â½ km deep (indications are it runs to a depth in excess of 2 km), is angled at 65-70 degrees towards the east. On one side, the surrounding rock consists of thrachy-andesitic vulcanites, mostly lavas. On the other, rhyo-dacite, often pyroclastic in nature.

The genesis is thought to be either magmatic or hydrothermal. The characterisitics of the ore body itself, texture and geochemistry, indicate a magmatic origin.

It is also the largest homogenous body of Iron ore currently known. Apologies for errors in translation, due to my lack of petrological schooling.

Dr K #33, thank you for answering my question. I figured that was the case. There seems to be the thought that if a quake occurs within a certain distance from a volcano, there will be an eruption or the quake will affect it for a later time. I guess it just depends on the magnitude, location, depth, and whether a volcano in the area is ready to go anyway. Thank you again for an interesting presentation on the Marianas.

Bruce #43, thank you so much for those links. I saved them in my favorites and I will be doing some reading. I had no idea there was a page from the USGS on subduction zones. The maps will help me see what is going on and the link to the study will be a help in understanding this stuff.

I wish I had taken more geology!!

ÃÃ³rÃ³lfsfell cam is showing a vigorous steam plume, but not so white.
BTW What happened to MÃºlakot cams?

A stack of earthquakes in Long Valley now. All right on top of each other, inside the caldera just to the West of Lake Crowley. http://earthquake.usgs.gov/earthquakes/recenteqsus/Maps/special/Long_Va…

Look at the Mammoth Lakes seismograph:
http://earthquake.usgs.gov/monitoring/helicorders/nca/94/latest/

>What happened to MÃºlakot cams?

*sigh* Webcam access was cut-off, after we crashed their server yet again last week. I think they got fed up with us, but there may be other reasons. Mulakot was a serendipitous view, never intended to support volcano monitoring from a globally distributed audience.

I'm not positive, but the steam seems to going down the hill following the old lava path--

Jen-- thanks for the heads up. I was thinking about going to Lava Beds Nat Monumnet next month, but perhaps long valley will be a little more interesting. :-)

Yeah, on thorolscam it looks like there may have been a lake breach.

@Renato -
The steaming is, indeed, vigorous - new water from the glacier; how and how much, I cannot say.

Yes, MÃºlakot webcams are off limits; they tightened the server access, which is a good move, securitywise: giving all the world access to your security camera views is not a good thing. At the moment there is only one view available and it sure does not point towards EyjafjallajÃ¶kull. The other cams might be available as well, but I've limited my hacking to just a direct view of that one feed's picture.

@parclair [56] -
You are right, only it's water that goes down the lava trench and the still-hot lava boils it away.

The reason for the steam being dark is heavy cloud cover.

@Lurking:

KirunafÃ¤lten and MalmfÃ¤lten Ironore fields are the largest and second largest iron ore-fields in the world.

The Kirunavaara-mine was from the beginning an 852 metre high mountain, today the mountain is gone and after a brief period of open pit mining they went down below, today they are preparing to start a level at 1350 metres below ground level.

Both the towns of Kiruna and Malmberget is being moved because of the risk of collaps is so large from the respective mines. The name of Malmberget mine is Kaptensgruvan (Captain's mine). The Captain's Hole is the worlds largest fault sink pit created by a blocking subsurface mine.

These 2 ore-fields (and a number of other ore-fields in the neighbourhood not being mined yet) was created 1,9 million years ago due to volcanic activity. Odd composition of the lava since the ore is above 50%FE, rich in phosphor and low on silicates and highly magnetitic.

The Kiruna-ore is a slanted slab 4km wide, 80m thick and confirmed to be 2 kilometres deep. No bottom is known to exist for it, and general assumption is that it continues pretty much continuously downwards without interuption. The geologists believe that the ore-body widens into a magma chamber at between 2 and 3 kilometres depth and some new bore-holes seem to validate this assumption. The chemical composition is the same for all of the known ore-bodies except the Luossavaara-ore. So most geologist believe that the known ore-fields join up deep down into one supermassive ore-body large enough to fill the entire planets need of iron ore for thousands of years.

If you ever want to see a mine... Go there, everything is one such a stumpingly min-boggling scale that the entire mind just go "Duh!"

Did I say that the mines are almost entirely automatic and run from above ground?
Of course this is the home of the rather famous Swedish Steel(TM) ;)

Sorry all for the redundant posting above, I missed that the other resident swede had answered upon our little national pride;)
He even bothered to get a source and I just used my tired old head and the memory of the geological reports I've read on the subject.
My interest in the mines are the unusually high tectonic activity.

Carl, (Intl Mines Inc etc, etc), definitely not redundant but rather, complementary, with lots of added and very interesting information. Heder!

Very true. The magma chamber referenced in post [61], is that as in "old" magma chamber? I doubt that anyone would even attempt to mine an active one. At a temp gradient of 1Â°C/30m that places the 3Km depth right at boiling. (I know the gradient varies depending on geology, this is just an eyeball guess)

Speaking of which... I have always wondered what an authoritative value is for the crust's average temperature gradient. The one I used is just some "thing" that ran across on the Internet while trying to debunk a "secret underground base" thread on another site. (BTW Passerby, that's where I came up with that idea) My logic was that it couldn't stay secret for very flippin' long with the amount of thermal energy that they would have to get rid of... no matter how advanced of a magical cooling system that they used. I think the gradient that I used was based on accounts of a silver mine out West.

I took a look at that mine in Google Earth and see that (at the time of the imagery) that it was mainly a trench cut through where the mountain was at. But if you make an assumption of a cone 852 meters high and 1000 meters across, then an inverted cone 1350 deep, that works out to about 6.9 billion metric tones if the rock has the density of basalt.

Now that's a lot of dirt. Has there been a noticeable change in seismically?

Gaffed by auto correct yet again.

*sigh.... "seismicity"

Wow Erik, this is a great volcano-mystery photo. Really difficult with many traps. I still think it could be Piton de la Fournaise, but this ist whishful-thinking. But I donÂ´t think it is Surtsey (no bamboo there). I compares fotos of Katia and Maurice Krafft and she had definetely little jug ears. And the hair of the guy in the middle could be Maurice Krafft because of the curly hair. I know they have been at the eruption at Heimaey but not at Surtsey. So it could be Eldfell, but I have never seen such a cone there. So if it is Katia and Maurice there, it could only be Piton de la Fournaise (which would have the nice side-effect, that I would habe win my first Volcano-Mystery contest) or Hawaii. Unfortunately there are also people form Island with jug ears, so IÂ´m afraid Boris Behncke could be right!

@Lurking in 64:

Yes that would be a 1,9 million year old magma chamber, if it really is a magma chamber there. It is still just a theory partly validated by one drilling. But it looks good. If I am correct it would be the first old magma chamber that was mined.

The gradient is lower in the Scandian mountains. Way lower. If I remember correctly the temperature at 1050 meters is 22 degres celcius with ambient rock temperature ten meters below surface being at 4... Would be around 1 degree per 75 meters.

The density is higher for iron ore than for basalt. The weight is 4.9 to 5.2 grams per kubic centimetre, basalt is 3. Generally the other stone around it is mostly granite.

The weight in ore (not counting grey-stone) hoisted out of the defunct mountain is actually 3.043.000.000 ton. The "mountain" you see on google earth is not the mountain, it is stapled grey-stone (mostly granite).

There has been a tremendous change. From pretty much seismically stable to daily seismic events ranging from 1 - 3.5. They thing the seismic event when the lake is going to fall down into the mine might exceed 5. And yes, they are prepared for a rather big lake falling down.

#60 @Kultsi, HyvÃ¤Ã¤ iltapÃ¤ivÃ¤Ã¤ ja kiitos!

#66 @Thomas: I've just copied and pasted your post to the other thread. Hope you're luky, my friend...

#37 @myke livers I've been watching at times Sakurajima webcams and I was lucky to see one small explosion. There are various cameras in the website, would you suggest one providing a better view? It takes a loong time to complete the buffering.

http://kagoshima-live.com/en/sakurajima.html

#70 @mike lyvers. My bad. :)

@41 (again): see answer, 48. I presume you were looking for a probable seismicity source.

@70 - try this link for the Japanese volcano. If the weather is good, you'll see some great roiling clouds of ash. http://tinyurl.com/23s47nv

#73 @santarosarita: Thank you very much for the link. Works great for me!

Yeah I uh... read 48. What about it?

Alright... another question comes to mind. I realize that the relative density of the oceanic crust is responsible for the it loosing out and becoming subducted in a convergence zone verses continental crust. I have also read that the Farallon plate made a shallow dive as it passed under North America. While poking around at the Aleutians quakes, I noted that the dip/dive angle seems a bit steep... the same for the Marianas. Is the dive angle a function of just how old (and dense) the oceanic crust happens to be, or is there another mechanism that decides that?

This one is the best Sakurajima webcam and it is erupting right now: http://webcam-svo2.pr.kyoto-u.ac.jp/local/camera.html

PS I had a quick look at it last night and saw quite a spray of glowing bombs!

@Mike, thank you very much for the link. It's easy to understand why there are so many cameras aimed at this spectacular volcano (not talking about who's sponsoring them) ;)
I'll wait till it gets dark to watch the show.

The tuna fishing on the reefs near Saipan is excellent. If you're the sort who like deep sea fish like marlin, you can catch 'em around there too. My colleagues observe the volcano(es) while I devour the fishies - occasionally they manage to drag me away from the table and get me to do some work.

@76 Lurking,
that's exactly the current thinking. The older the crust, the cooler and more dense it becomes. Young hot crust, such as you get in Cascadia, is more buoyant and has more difficulty.

EKoh 81: so presumably that's why (from your diagram in Part 1) the Jurassic-age oceanic crust of one plate was subducted below the younger Eocene oceanic crust of the other? Or are there other factors at work?

#27 #28 @Lurking: KHABAROVSKIY KRAY, RUSSIA EQ has been removed from EMSC. No traces, no explanation. (???)

Hmm... three possibilities.

1) Analysis of the waveform showed that it was an intercept of a different quake form somewhere else or noise, such as can be found from a bolide exploding (simultaneous intercepts on multiple seismos)

2) Super-Secret underground testing, ignored by other countries since they don't want the hassle or the political problems involved in dealing with it

3) Aliens.

I vote for #1.

#84 Very interesting, indeed. Seismicity has been very high over the last days. Waves are getting interlaced, seismographs go bamboozled. I only think it's weird considering a mag. 6 quake. And it stayed there for almost 24 hours until they noticed. OK. There have been no after shocks after this one, so probably just a misinterpretation of the signals.

@85

Well, there was an event not too long ago that put a tsunami alert out for Florida and the East coast from a MASSIVE quake in or around Hispaniola. Turns out it was some one doing tests on some reporting equipment and the auto alert portion of it did what it was supposed to. But there was no quake.

It's not like some idiot held an electric razor up to the underwater microphone while their ship was steaming in formation...

(from what I understand, it sounds just like a torpedo... which explains why everybody broke formation at the same time)

#86 Yes, I remember that one. A 8+ in Dominican Republic, but it was quickly deleted. But this one... humm... a torpedo... that sounds quite possible... like on the edge of a bowling lane :)

And there was another shallow 2.0 at BÃ¡sar... maybe an UFO colliding with the glacier. :)

@Renato Rio [86]

Ooops... I forgot, there is a 4th possibility.

Graboids.

http://www.imdb.com/title/tt0100814/

#89 Graboids! Could never have imagined... :)

@Lurking:

I loved the documentary TV-series on the Graboids:)

This sounds wonderful. I'm just chilling in my own hotel room in Killarney looking at a lot of these opinions. Many are great and many fail to help to make a lot real sense in the least. We are on a break however , I just could not help myself away from taking a look at this blog site notwithstanding my hotel room now in Killarney charges on-line usage allowance by the hour.hotels in killarney co kerry,list of hotels in killarney ireland

A volcanic cruise through the Mariana Islands: Part 1

eklemetti — Tue, 13 Jul 2010 02:10:00 +0000

A volcanic cruise through the Mariana Islands: Part 1

This week I welcome Dr. Ed Kohut as a guest blogger here on Eruptions (while I am off in the Sierras doing some field work). I've known Ed for 10 years now - we were both graduate students in igneous petrology at Oregon State University - and we are both Massachusetts natives. Ed was in the Coast Guard before getting degrees at University of Rhode Island and Boston University before heading of to Oregon State for a Ph.D., where he worked on melt inclusions in minerals. One of his major research areas is magmatism in the Mariana Islands and he was nice enough to put together a look at the Marianas for Eruptions - this is Part 1. Enjoy!

------
Big thanks to Erik for inviting me to post a bit on the Marianas. I have been working in the Marianas since 2001 and I have to extend gratitude to Sherm Bloomer at OSU and Bob Stern at UTDallas for not only getting my involved to begin with, but also for keeping me involved. I hope to show that there is a lot more to the Marianas than just the trench.

What, Where
If you look at a map or a globe, you will see many long chains of nearly regularly spaced islands, particularly in the Pacific. Some of the chains are curved to form an arc shape, and are the origin of the term island arc. Since these islands are largely volcanic, they are also the source of the geologic term "volcanic arc". These arcs are the volcanic expression of subduction zones (more on that later). The Western Pacific is home to several of these arcs, including the Marianas.

General location map of the Mariana Islands in the Pacific Basin. Click on image to see a larger version.

The Marianas Islands lie south of Japan and run ~750 km from Guam to the Bonin Islands. The larger southernmost islands (Guam, Rota, Saipan, and Tinian), are uplifted volcanic and carbonate rock and are not part of the active volcanic arc. The more northern islands are active volcanoes that have built up from the seafloor. Several of the larger submarine volcanoes were historically noted as shallow banks. The Marianas are part of an extended series of three subduction zones, Izu, Bonin and Mariana, that are known as the IBM system and are the focus of ongoing research.

First, a little human history. Geographically the islands are part of Micronesia and the original inhabitants are the Chamorros. The Chamorro way of life dramatically changed on March 6, 1521 when Ferdinand Magellan landed in Umatac Bay, Guam during his expedition's circumnavigation (crazy as it sounds, Guam was the first land they touched since leaving South America). Spain eventually formally claimed the islands in 1667, ushering in 231 years of Spanish rule. Defeat in the Spanish-American War forced Spain to cede Guam to the U.S. in 1898 and sell rest of the islands were to Germany. As a result of Germany's defeat in WWI, Japan was given the northern islands as a League of Nations Mandate. Guam was taken by Japan on Dec. 8, 1941. Major battles in 1944 resulted in the destruction of Japanese naval air power and bloody amphibious assaults on the Guam, Saipan and Tinian. Tinian became a major U.S. airbase and the atomic bombing missions in 1945 originated from there. After the war, Guam returned to U.S. territorial status and the northern islands eventually became the U.S. Commonwealth of the Northern Mariana Islands. During the period of recorded history, eruptions have occurred on Asuncion, Agrigan, Pagan, Guguan, Sarigan and Anatahan Islands.

Why
The reason for the islands and the volcanoes is the process of subduction. To get subduction you need to have two plates converging, plates being the crust and uppermost mantle, called the lithopshere . The lithosphere is above another layer of mantle called the asthenopshere, where the rock is at just the right pressure and temperature to flow over time and help move the plates. One plate then begins to go down under (subducts) the other. The leading edge of the continental plate must be basaltic oceanic crust, continental crust is less dense and too buoyant to go under the mantle. In the Marianas the Pacific Plate is subducting westward under the Philippine Plate. As the subducting plate (or slab) sinks, it slowly warms. Water in crust, in minerals, and in any sediments along for the ride is released in to the mantle of the overlying plate. This water forms new minerals that are then dragged deeper as the process continues. Around 80-120 km deep, these minerals breakdown and release the water into the surrounding mantle rock. At this depth, water promotes melting of the rock and we have magma. Since this occurs at same depth along the subduction zone a chain of volcanoes develops. The magmas start off with abundant water and CO₂, and are often thicker andesitic and dacitic magmas that will hold onto the volatiles until reaching the surface. As a result, subduction zone arc volcanoes often produce explosive Vulcanian to Plinian events.

Schematic cross section of the Mariana Islands subduction zone. Click on the image to see a larger version.

Looking at the cross-section, you'll notice a couple of other features. Where the plates meet a depression forms in the seafloor - a trench. The sides of the trench are not as steep as imagined since drawings often have vertical exaggeration, they are usually around 8 to 10x wider than they are deep. The Marianas Trench is famous as the deepest point in the Earth's oceans (10,916 meters or 35,814 ft). Beyond the trench is the forearc, an area of compression, folding and thrust faulting. Huge megathrust quakes such as the 2004 Indonesian quake and resulting tsunami originate in these areas. Then we have the arc itself. Behind that there may be an area of rifting appropriately named the back-arc basin. Back-arc basins operate much like mid-ocean ridges, but exist for different reasons. In the Marianas, the Phillipine Plate itself is subducting on its NW edge and being pulled in that direction at the same time it is converging with Pacific Plate:

Plate motions at the Philippine Sea. Click on image to see larger version.

The difference in movement creates tension within the Marianas Subduction Zone, resulting in a rifting of the arc not once but twice. Rifting of the old arc left fragments in the present fore-arc, these bits have been uplifted to form the Guam, Saipan, Tinian and Rota. The arc began rifting again ~7 million years ago and eventually opened to form the current Mariana Trough back-arc basin (not to be confused with the Mariana Trench!)

Subduction history of the IBM.

The Marianas, together with the rest of the IBM, is largely free of interaction with continental crust and sediments. As a result, the cycling of water, CO₂, chlorine, sulfur and silicate material between the mantle , crust, oceans and atmosphere in subduction zones can be examined and all stages of back-arc development are present in the IBM as a whole. The Marianas then are much more than a deep spot in the oceans and are an exciting place to visit and work.

Next I'll give you a tour of the volcanoes!

eklemetti Mon, 07/12/2010 - 22:10

Tags

Thanks, doc Ed!

That was a very informative condensation of what, where and why of the oceanic subduction mechanics; 'specially it explains why the deepest point in oceans is connected with subduction.

We are all very happy to welcome you, Dr. Ed. And bringing to your opening night such an illuminating subject.

Dr. K, thank you for informative post. You've given me an explanation of the asthenopshere that explains what it is and why it exists. So, do the pressure/temperature gradients vary from subduction zone to zone? can it vary within a subduction zone? Is there a fixed range of pressure/temperature? Thank you.

Thank you, Dr. K for introducing an interesting subject. I have been hearing about the Marianas and I have wanted to know more about them and get an idea of not only where they are (I didn't know that Guam was part of them), but how they formed. As I was looking at the map of plate motions in the area, I was thinking what a mess it is with all the different directions of plate movements. It is no wonder why there is so much volcanic and earthquake activity in the area.

I look forward to your next post.

Hello to all,
Welcome Dr Kohut.Subduction and the ever changing face of planet Earth has been a source of fascination for me for a long time and I read your first post regarding The Marianas with great interest.
What will this planet look like in the next 100 million years or so ? Fundamentally different to how she is now.
I look forward to further posts with anticipation.

Umm,i've just been reading an interesting piece on Iceland Review,link is http://www.icelandreview.com/icelandreview/daily_news/?cat_id=29314&ew_…

Let me explain.After the controversy yesterday,I think that what I saw on the left of d9tRotterdam's time-lapse video from Mulakot cam was the "ghost" or even an "echo" from FimmvÃ¶rduhÃ¡ls.
I believe that the "plume" that I saw was in fact a large amount of steam rising from the FimmvÃ¶rduhÃ¡ls site,as explained by the article itself and what is said by the Hikers interviewed.
So,no new activity from anywhere,just a "blast from the past".

Please post your off-topic comments to the Open Thread.

Thank you for that explanation. I knew about volcanic arcs arising from subduction zones, but was confused by the term "back-arc". I need to go and re read some previous links now with a fresh eye.

@8:
Congratulations, you have won a spanking brand new bubblegum-machine filled with scout-cookies.

Thank you for a beautifully written, interesting and informative article.

As Paul says, thank you for an article so beautifully written, interesting and informative that even Passerby will enjoy reading it.

:mischief:

Hey!! EKoH!! Great to see you stepping in for Erik. I was wondering where you were and then you serve up this delicious course for us! Funny, how even when I read the basics again, I still learn new stuff (all credit to you I might add). For instance I didn't realize the upper asthenosphere moved in line with the plates. I had always assumed the lithosphere was decoupled from the asthenosphere at the Moho and that the plates were moving across it as this explains hot spot-related volcanic chains... oh dang it, must have got it wrong again. How do hot spots work if the aesthenosphere itself moves? Is it because the asthenosphere itself is not very thick?

BTW the way a volcanic forms at the 100km depth contour of the subducting plate is beautifully illustrated in Japan in this movie by Ross Stein et al that I chanced upon two days ago:

http://sicarius.wr.usgs.gov/fragment/download.html

Another question, the Kermadecs and the Havre Trough interest me, particularly if you follow the ridges down into New Zealand as they line up beautifully with the TVZ on the one hand (which is line with the arc of the Kermadec Islands) and Taranaki and Mayor Island on the other hand which is in line with the ridge marking the western border of the Havre Trough. My question: this western margin of the Havre Trough, is this also formed by rifting as you illustrate above for the IBM and if so, is there any connection between the associated faulting and the western arc of volcanism in New Zealand (i.e. Taranaki, Mayor Island?

My point being, that given that volcanos form above the approx. 100km depth contour of a subducting slab, is this evidence for subduction of a microslab west of the TVZ, it's margins being delineated by the rifting found in the Havre Trough? ok, I'm postulating wildly here, guess I better rein myself in a bit.. ;-)

me again, re that last little postulation, I just checked out the seismic records from Geonet again and I can't see any evidence for a subduction of a microslab.. which begs the question: why is Taranaki there?

Hi Bruce,
Tonga Kermadec is also a complex little world of subduction and multiple rifts. I'll check on your questions and see what I can find.
The asthenosphere is a particularly weak part of the mantle that is a few 100 km thick. It does flow, not only from back arc to arc and the down, but parallel to the arc in some places. It also upwells under mid-ocean ridges and back-arcs. The mantle plumes that a presumed to be the source of many hotspots are supposed to originate deeper in the mantle.

Erik should do something on hotspots and the plume idea and debate - that'll teach him to confuse BU with BC ;)

Ed Kohut

To all readers, I will try to answer any question through the comments section.
I should add that Dr. Yoshi Tamura at IFREE in Japan is also an important investigator in the Marianas and has done a lot to propose and schedule research cruises to the area.

Ed Kohut

Thanks EKoh!

I take it that the circulation in the asthenosphere from back arc to arc then down then upwelling in the back-arc basin is also at least partly driven by friction against the submerging plate (i.e. not only does the collision throw up an accretionary wedge but it also drags asthenosphere down with it. Is this right?

What an excellent volcanic cruise. I look foward to subsequent installments!

@Bruce stout: the movie by Ros Stein is amazing. Thanks for posting. Wish @Lurking could take a look at this.
And thank you very much EKoh for sharing your knowledge with us.

hi everyone

Today there was a earthquake at laki volcano. the depth was at 1.1 km and the mag. was a 2.2. This could be tectonic more than magmatic but something to keep watching.

Are there any examples of back-arc distinct volcanoes or are they just spreading-center vents?

I think the article was fantastic. I had heard the back arc / fore arc terminology used in discussions of the Sumatra Shindig, and had murkily worked out what they meant. This provided "back-fill" that explained what I was reading. THANKS!

OT: @jack [20] Laki and the Technonicsâ¢ I'm not that sure that a tectonic event at Laki/EldgjÃ¡ would be a very good thing. 934 and 1783 didn't turn out so well.

Here is a cross section pretty much perpendicular to the ERZ. Lat/Long coordinates omitted to eliminate some confusion. The view angle is approximately 307Â° (looking to the North West)

http://i28.tinypic.com/25tc5dt.png

Oops... those are all July quakes to present.

By chance I have been doing some introductory reading about geodynamics. It is a fascinating story that is becoming as confusing as it is enlightening.

Kultsi(1)says that EKoH has explained why the deepest parts of oceans are subduction zones.

I don't easily see it but assume that such deep places are caused by subduction in contact between two or more 'dense', thin, structurally resilient oceanic plates.

There are many other processes involved and I allow myself the opportunity to go perceptually dyslexic and fall back into confusion.

Most everything in volcanology could be attributed to state change and the annealing/quenching brought about by flux in the respective factor. (factor = temperature, gas concentration, chemical concentration, pressure, ? )

'State change' as in melting/solidifying and 'flux' as in temperature and thermal transport keep emerging as the main factors. Numerical simulations show that rifting is particularly sensitive to establishing and maintaining a thermal flux.

This leads me to consider some fanciful questions as a means of rapidly setting context.

- How deep does an ocean have to be before the pressure does away with the lithosphere altogether and problem is reduced to a liquid/liquid water/mantle phase boundary? Obviously the water acts as a calorimeter sink and the existence of a liquid/liquid interface is implausible, yet as the lithosphere transformation is described in the topic introduction, the deepest part of the deep oceans of 2 miles of liquid. ... Let's just say there seem to be limits as to how deep an ocean can become. Remember that the situation is a liquid floating on top of a plastic lithosphere floating on top of a fluid mantle.

- The question is more interesting when one considers ice ages and polar ice caps. I don't know if ice sheets of a 100 miles thickness are implausible but the scenario must have interesting consequences for plate tectonics and continental drift.

- 80% (??) the bulk of the heat flux is derived from radiogenic activity in the lithosphere (natural radioactivity).

Here are some crude heat flux values in units of watts per square meter.

Sunlight falling on the earth = 60 watts/m^2

Non 'hot spot' ( i.e. most of the earth's surface) derived from the earth's interior + radiogenic activity = 10's of milliwatts/m^2

Tectonically active regions = 100 milliwatts/m^2

"Restive" volcanoes on active faults with aqueous lakes = a few 10s of watts/m^2

It is intriguing to see that thermal fluxes that determine tectonic activity are of order(s) of magnitude less than the thermal fluxes involved in climatological process.

Or rather that factors and processes involved in attenuating or augmenting thermal fluxes at a scale of .1 W/m^2 are everything.

Perhaps it explains why most of the the plate boundaries are submersed and that the rising and continued evolution of an eruptive fault line above the water table has a big influence on the future evolution of faults.

Given a low globally averaged subterranean derived thermal flux of ~ 30 mW/m^2 there would seem to be ample opportunity for coupling with climatological, biological and extraterrestrial activities in regard to 'hot spot' and fault line evolution.

It certainly is a complex system. There are coupled interactions at length scales ranging from the microscopic to the astronomical.

For example, it would seem that even a small asteroid impact could change the future evolution considerably. Alternately the many many scales of coupled interactions ( many phase states are involved at many scales) might serve to buffer and re-establish a dynamic 'quasi equilibrium'

Ocean crust = 5 mi
Continental crust = 25 mi average thickness.

Now who do you think will win a pissing (convergent plate) stress contest?

On the theory of subduction with mechanics explanation, see 'Origin' section, with recent references:

en.wikipedia.org/wiki/Subduction

Talking about subduction, looks like aftershocks on Chilean EQ have risen since yesterday: 6 EQs over 5+

At the bottom of the 'Subduction' wikipage, you may have seen Tatsumi's humorous cartoon diagram of ocean crust processing. Two papers worth a read:

Manufacturing Continental Crust in the Subduction Factory. Tatsumi, 2006 Oceanography 19:104-112.

www.tos.org/oceanography/issues/issue_archive/issue_pdfs/19_4/19.4_tats…

Original 2005 Tatsumi classic, www.geosociety.org/gsatoday/archive/15/

An Overview of the Izu-Bonin-Mariana Subduction Factory (2003)

ftp.utdallas.edu/~rjstern/pdfs/IBMoverview.pdf

Not sure I follow your logic on 'how deep an ocean can be'. The constraints lie in the formation of the oceans and large -scale hydrologic cycles over time (evaporation vs condensation, which can be evaluated by isotopic ratios, see Rayleigh Fractionation).

Ice sheets during the last glaciation cycle: 3.5-4 Km, northern hemisphere.

Thickness of the Antarctic Ice Sheet
hypertextbook.com/facts/2000/MaySy.shtml

That icecap as quite a bit to do with both salinity and thermal behavior of the deep oceans.

moregrumbinescience.blogspot.com/2010/03/why-is-ocean-cold.html

The lithosphere is dense, but not as strong as the lithosphere. I do not think 'ocean depth weight' is an issue.

The answer to your question then, is found in the process by which the oceans formed:

www.chem.duke.edu/~jds/cruise_chem/oceans/ocean1.html

The rate limiting step would be the mass and composition of the early atmosphere and the rate of cooling that allowed condensation to form.

And of course, it would require a gravity field.

Wow,the mantle certainly doesn't seem to be the viscous undifferentiated fuzzy warm body I learned about 40 years ago.

Are the interior of stars still viewed as warm fuzzy fluid balls being too hot for differentiated structure formation? I.E. ..such as http://library.thinkquest.org/27930/media/sundiagram3.gif

Continuing to read. ...

Thanks Passerby

I would be seriously remiss if I didn't add a truly elegant paper by Udipi Ramachandra Rao that explains the importance of the magnetic field in maintaining the water and ozone balance in the atmosphere while limiting NOx formation.

Big Picture perspective is always useful.

Crucial role of the magnetic field in the evolution of life. www.ias.ac.in/jarch/pramana/15/00000038.pdf

Minor wording correction: The relatively rigid lithosphere is dense, but not as strong as the aesthenosphere.

Sorry, can't answer your question on modern theory of star formation. Not my bailiwick.

>the mantle certainly doesn't seem to be the viscous undifferentiated fuzzy

We're hoping our guest host will shed some explanatory light on this complex topic.

But first, island arcs and island volcanics.

@Passerby - Re: Stars

Current ideas are that no, Stars are just as differentiated as our Sun. Via Helioseismology, they have deduced that the Sun has two different rotations. The upper Differential rotation area where the poled rotate slower than the Sun's equator, and an inner region that rotates as a solid body.. not that it's necessarily solid, just that it rotates uniformly from pole to pole. It's also though that the turbulence where these two regions interact is responsible for the Solar dynamo, and the sunspot cycles. Since stars have been seen to exhibit similar periodicity, the general idea is that they operate in a similar manner.

Sorry... meant to be @Raving. My bad.

A good read:

"Sunquakes: Probing the Interior of the Sun" - J. B. Zirker

The mantle is made of a family of rocks called peridotites. These are made of dense silcate minerals with lots of magnesium and iron. There are variations in places due to some material being removed by partial melting. There are some changes in minerals with depth as one mineral becomes unstable and changes to a more stable one. Then there is subducted oceanic crust which metamorphoses from basalt and gabbro to a rock called eclogite. There are also global isotopic differences that make mantle types called things like HIMU and FOZO by that strange group, mantle petrologists ;)
But compared to continental crust, mantle rock is remarkedly homogeneous.

The Wikipedia pages are not bad:
http://en.wikipedia.org/wiki/Peridotite
http://en.wikipedia.org/wiki/Eclogite

Ed Kohut

@Ekoh I haven't looked at those references yet but what you have written clears up and/or adds confusion immediately ... oh the joy and the confusion ... solid/solid exothermic phase transition ... compressive (kinetic heat) exothermic phase change of subducted material originating from convergence and subduction of plates (more release of kinetic energy)... deeper down close to the outer core an endothermic state change. ...

... "mantle rock is remarkedly homogeneous" ....

X-|

Dr. Kohut, welcome, and thanks for the informative post and especially for making geochemistry interesting and sensible. That last section, about why the Marianas are so helpful to study, is doubly enjoyable for me and here's why.

Back in the 1980s, I tried to get an undergraduate degree in geology but just could not grok geochemistry - even mineralogy was tough! It is science articles like this, written in plain English, that help me see how the chemistry fits in with all the rest of it (which I truly love and did well in academically).

Great design first thingâ¦ Second thing the prespective at which you see the sport is quite neutral quite in my words wikipedia style. This is a welcome change from people who are either racist or support a particular agenda.!

I admire what you have done here. I like the part where you say you are doing this to give back but I would assume by all the responses that this is working for you as well. Respectfully, Sean.

Eruptions Summer Schedule

eklemetti — Fri, 09 Jul 2010 13:12:42 +0000

Eruptions Summer Schedule

Mineral King valley in California.

Well, we are in the peak of the summer, so Eruptions will be running a bit of summer schedule while I'm off away from the interweb tubes. First off, from July 11-20, I'll be off in the mountains, doing some much-needed fieldwork with my (first) undergraduate research student. We'll be up in the Mineral King area of Sequoia National Park looking at some old rhyolites and granites - we're talking Triassic and Jurassic submarine and subaerial calderas! We'll hopefully be taking a look at zircons in these rocks to help constrain the timescales of these enigmatic early "Sierran" volcanics (all as a part of a larger Keck Project).

While I'm out in the field, look for some posts that will show up (hopefully automatically):
- Guest blogger Dr. Ed Kohut will give us a tour of the Mariana Islands and magma genesis in that volcanic arc.
- A new Eruptions Word of the Day.
- Mystery volcano photos that will hopefully stump more of you.
- And an open thread for you to post in case something exciting happens ... or to discuss whatever volcanic topics catch your fancy.

Enjoy the summer while I'm out in the rocks ... !

eklemetti Fri, 07/09/2010 - 09:12

Tags

Enjoy your fieldwork Erik, hope the weather holds up for you.

Bon Voyage and welcome to Sunny CA. The weather has been remarkably mild this year, in Lassen some of the roads are still shut due to snow. It should be lovely in the mountains.

Erik, it's so Finnish to get off for a (four weeks) while! :D

Enjoy; summer's just once a year, while fall & winter are there every year!

Erik,
Have a wonderful Holiday,even if it is a slightly "working" one.You've earnt it !

Adrian.

Erik, enjoy yourself and enjoy introducing your student to your field. Other half will be on Victoria Island NWT doing sill studies (Minto Inlier) starting Monday. We'll hold the fort and wait to hear about the summers' work.

It's worthwhile having a catch up on Dave's Landslide Blog
http://www.daveslandslideblog.blogspot.com/

He has some great ice collapse links including a foretaste of what will happen to Helen's arch at Eyja.

Have fun visiting the Keck project!!! Say hi to any F&M'ers for me

Good zircon hunting, Erik! Ar least CA in summer shouldn't be hampered by bad weather. Looking forward to your guest blogger, since the Marianas seems to be both highly active and little reported, maybe because so many of its volcanoes are submarine

Erik! i envy you!

I was in Sequoia National Park when i was just 8 :(
I remember a lot of things in it but...not geologic ones.
I hope that you will make a lot of photos and you or a your student will show them to us.

Have a nice trip

Erik I've been to Mineral King many times, though long ago. The White Chief Caves (in marble) are really fun to explore so bring your caving gear if you've got any. And there are about a zillion fossils high up on one of the mountains nearby.

A few weeks back there was some discussion about volcanic tremor at the New Zealand volcanoes,...which turned out to be wind noise. Well,...now that the wind has apparently died down down under,...true volcanic tremor is visible on the Ruapehu and White Island seismometers. This is "normal" activity for both volcanoes but,...it's best not to ignore a rumbling volcano!

A few mid-June pics I hadn't seen before of glacier & crater lake at http://www.earthice.hi.is/Apps/WebObjects/HI.woa/wa/dp?pictureID=101645…

With the above normal snow pack this year, mid-July should mean clouds of mosquitos in the head waters of the Kern and Kahweah rivers. Don't forget your DEET!

Enjoy the vistas of the Kahweah Peaks Ridge to the northeast of Mineral King! The deep red and black coloration of the metavolcanic roof pendant stand out strikingly against a sea of glacially carved Sierran granites.

Don't forget about the Quaternary volcaninc field (Toowa Volcanics) just a few miles to the east of the Kern River canyon in the Golden Trout Creek drainage just southeast of the park boundary! I've always wondered about the origin of these cinders cones and basalt flows atop the middle of the Sierran batholith?

Enjoy the rocks while us stay-at-homes mess about online! Thanks for providing us with some entertainment while you are in the field.

Nice steam plume atop Lady Eyja this morning... beautiful view for any of those looking at Hvolsvelli cam :)

@Yes, Helen We are all happy to see Lady E back to action. I'ts just a light steam plume, but the steam and the puffing provides beautiful color patterns at sunlight. So far we think it's just water filling the cracks, still filled with hot lava.

Someone take a look at the Katla cam. Looks like a steam plume and possible vent to my untrained eye.

Hmmm far left on Katla cam... shadow or dark cloud?

... dark cloud....

Erik,
Who is doing your the zircon geochronology? If you're interested in possible edimentary recycling into the magma, make sure you also get oxygen and hafnium isoqtopes done.
cheers,
Chuck

Hey that's an amazing insight on the subject, thanks so much! never heard it more clear.

There's a reason I can't do both at the same time: premature ejaculation

monday morning at work is like getting woken up by someone hitting you in the face with a piece of wet fish

For the record I've seen your page or blog before and I'm confused as to why I didn't add it as a bookmark before because organized and it's well constructed. If you aren't busy can you take a look at my blog sometime or email me back with help or suggestions as to what I could improve upon on my site. Thanks.

Express gratitude against this strategies outstanding assess; this can be the species of pace that a lot of prevents my lifestyle planned out of wedding.I have without doing awkward exorcizes sustained been for a while requiring on the market within your web-site precise after Document realised of all these because of a dear sibling and even were basically lucky lake is at a huge placing to get the house correct shortly afterwards searching for for a long time. Being a n expert tumblr, Therefore i'm ecstatic to locate done some friends acquiring gumption in addition to adding more into the local region. I merely wanted to research to provide brand new love indoors your submit as it's remarkably pressuring, and as a result hundreds of world-wide-web novelists usually do not produce your credit standing individuals may like to posses. I know for constructive See come back ever again which will then watercraft released many of several other relatives.

Things you brought up seems sensible. Nonetheless, think about this, what happens if you offered a little bit more? What i'm saying is, I do not tend to tell you how to write your blog, however what if you added extra content that can certainly get people's notice? Just simply like a online video or possibly a image or 2 to have viewers interested regarding what you are talking about.

Hah Ein Tropfen auf den heiÃen Stein - Anyone who has lost track of time when using a computer knows the propensity to dream, the urge to make dreams come true and the tendency to miss lunch. Attributed to Tim BernersLee

Ask Sally Kuhn Sennert (Global Volcanism Program) your questions!

eklemetti — Wed, 23 Jun 2010 01:06:09 +0000

Ask Sally Kuhn Sennert (Global Volcanism Program) your questions!

As a part of my continuing Q&A series, I am pleased to announce that Sally Kuhn Sennert, compiler and author of the weekly Global Volcanism Program Volcanic Activity Reports, is the next up to take your questions. A little bit about Sally:

Sally Kuhn Sennert graduated with a Bachelor's degree in Anthropology from the University of Pittsburgh in 1997. She worked with non-human primates for several years before deciding to switch gears and pursue her first love, Geology. She returned to the University of Pittsburgh, and completed her Master's degree in 2003 under the direction of Dr. Mike Ramsey. The focus of her work was to map changes in glassy and vesiculated textures across the Soufriere Hills lava-dome surface over time, using thermal infrared images captured by the ASTER satellite, and compare her findings to other eruption data, and ultimately to evaluate hazard potential. Currently, she is at the Department of Mineral Sciences in the National Museum of Natural History, where she has been writing the Weekly Volcanic Activity Report for the past four years. Sally's position represents cooperation between the Smithsonian's Global Volcanism Program and the US Geological Survey's Volcano Hazard Program.

I know many of you read the reports diligently every week, so here's your chance to ask Sally about her work, what its like to put the reports together or anything else you think might be interesting to ask. Send your questions to and I'll collect your questions until June 30 when I'll send selected questions off to Sally to answer.

If you want to browse some of the other Q&A columns, check them out:

Send in those questions!

eklemetti Tue, 06/22/2010 - 21:06

Tags

class participation

Global Volcanism Program

Q&A

Smithsonian Institution

Steve, Leeds, UK
Hi. I read your weekly report without fail every Thursday. But there has always been one thing I would like to know. That is that some volcanoes like Karangatang or Stromboli, ehich have been erupting almost constantly for decades or even years. Somtime warrent (New Activity) status. For example this week (17th - 23rd June 2010) you have put Bezymiany into this catagory, although the activity that is been documented is not anything unusual, with reguards this volcano's activity since the 1950's. That is periods of dome growth interupted by Vulcanian explosions accompanied by pyroclastic flows, pyroclastic fall deposits, and the occasional thick blocky lava flow.

Man this is a lonely thread.

Just to keep it from feeling neglected, here is a plot if Iceland's 15 minute quake energy from the 15th until now.

http://i49.tinypic.com/fdccqg.png

JÃ³n FrÃmann from Iceland.

Why are there sometimes unfinished or outdated information on the Global Volcanism Program web site ?

Thanks.

Historical background of the GVP Weekly Reports and technical perspective are helpful.

About the Smithsonian Institutes's GVP Volcanic Activity Reports:

www.volcano.si.edu/info/about/about_reports.cfm

Basis of professional interaction between the USGS Volcano Hazard Program and the SI GVP:

GVP Weekly Reports Criteria and Disclaimers webpage
http://www.volcano.si.edu/reports/usgs/index.cfm?content=disclaimers

Technical-Information Products for a National Volcano Early Warning System. US Geological Survey Open-File Report 2007â1250 (2007). Especially useful information in the Appendix material on Aviation monitoring.

pubs.usgs.gov/of/2007/1250/

USGS Volcano Hazards Program
volcanoes.usgs.gov/

Why the USGS monitors volcanoes (webpage)
volcanoes.usgs.gov/about/faq/faqmonitoring.php

Lastly, the Eruptions blog relies heavily on catalog material provided by the SI-GVP. That catalog was compiled by two exceptionally noteworthy volcanologists: Tom Simkin and Lee Siebert. Lee became the GVP director in 2007. Tom, who passed away just a bit over a year ago, was GVP director from the late 60s to the early 1990s.

http://www.volcano.si.edu/info/simkin/

Simkin T, Siebert L (1994) Volcanoes of the World (2nd edition) Tucson: Geoscience Press, 369 pp.

Updated and digitally complied catalog:
Siebert L, Simkin T (2002-) Volcanoes of the World: an Illustrated Catalog of Holocene Volcanoes and their Eruptions. Smithsonian Institution, Global Volcanism Program Digital Information Series, GVP-3.

Lastly, Lee and Tom crafted an especially insightful article, 'Volcano Fatalities--Lessons from the Historical Record', published in the journal, Science (Jan 2001, Vol. 291. no. 5502, p. 255 DOI: 10.1126/science.291.5502.255)

The sole figure of this policy paper graphically illustrates the exponential rise between number of fatal eruptions (Fig 1A) and cumulative fatality (Fig 1B) between the 14th and 20th centuries.

Most telling, is the lag in fatalities, with 2/3rds of the fatalities and one-half of the fatal events occurring more than a month after the initial eruption, the result of growing cynicism among locals towards tephra, mudflows/lahar and and ash hazards.

Perhaps Sally Kuhn Sennert, the GVP or someone with an account on the aviation forums might wish to advise those interested parties that KVERT and it's aviation reports will soon cease to exist.

Alternately, there does not seem to be awareness in commercial aviation of KVERT. They won't know what they will be missing.

http://www.airliners.net/aviation-forums/general_aviation/search.main?s…

-----------------------

Hmmm, I wonder if NOAA will notice the departure of one of their data sources.

Subject: FVFE01 RJTD 240204

FVFE01 RJTD 240204 2010175 0206
VA ADVISORY
DTG: 20100624/0204Z
VAAC: TOKYO
VOLCANO: KLIUCHEVSKOI 1000-26
PSN: N5603E16038
AREA: RUSSIA
SUMMIT ELEV: 4835M
ADVISORY NR: 2010/46
INFO SOURCE: MTSAT-1R KVERT
AVIATION COLOUR CODE: NIL
ERUPTION DETAILS: POSSIBLE ERUPTION OBS AT 20100623/2232Z FL190 ON
SA
TELLITE IMAGERY.
OBS VA DTG: 24/0059Z
OBS VA CLD: UNKNOWN/FL190 N5614E16052-N5707E16204-N5702E16238-N5612E1
6143 MOV NE 20KT
FCST VA CLD +6HR: 24/0659Z SFC/FL200 N5700E16230-N5658E16428-N5830E16
430-N5831E16230 FL200/550 NO VA EXP
FCST VA CLD +12HR: 24/1259Z SFC/FL200 N6042E16603-N5830E16600-N5830E1
6400-N5945E16355 FL200/550 NO VA EXP
FCST VA CLD +18HR: 24/1859Z SFC/FL200 N5948E16628-N6019E16801-N6200E1
6800-N6200E16630 FL200/550 NO VA EXP
RMK: NIL
NXT ADVISORY: 20100624/0600Z=

www.ssd.noaa.gov/VAAC/OTH/JP/MSG1750207.01.txt

When someone says 'wait for it...' as a comedic device, it's even funnier to just kick them in the crotch real fast.

That is getting a bit extra subjective, but I greatly desire the Zune Advertise. The boundary can be lively, will have extra aptitude, and several settle benefits wish 'Mixview' that allow you to rapidly view related cds, music, and sometimes a other slimmers in connection with any you're listening to. Clicking on a single of those would base on that object, and another set of "neighbors" will come into panorama, allowing you to cross here longing in equivalent artists, tune, as well as consumers. Speaking of operators, the Zune "Community" is also great fun, putting you discover other products together with public tastes and becoming associates with each other. And then might hear a playlist designed based on a new combination of what all your friends are listening to, that is definitely moreover wonderful. A lot of approximately privacy will be solved discover it is possible to prevent the public away from experiencing your personal listening behavior in case you therefore decide on.

Good day, i'd guess that may be from content truthfully at any rate, patient looking encompassing your website or blog it seems to be pretty basically tidy. So i'm creating a creative thoughts or hurting get back look great, whenever we all impression a bit my partner screw it up. In which way fast was indeed it then set up site? Can a person much like me getting valuable experience do so, in addition to give household improve web sites with no need of endangering they each and every time?

Thing you are talking about made . But, picture this, what if you integrated a little bit more? What i'm saying is, I don't tend to teach how to write your site, but if you added something that can certainly get peoples awareness? Just like a video clip or simply a image or 2 to get people excited concerning what you mentioned.