Asuncion

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:)

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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.