Eruptions

Monday Musings

Posted by Erik Klemetti on August 17, 2009
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I knew that the minute I said I’d be back to a “regular” posting schedule that I would fail miserably, so maybe the less said, the better.


Cerro Galan caldera in Argentina (taken from space).

Thanks to all the readers who have been avidly discussing a number of fascinating topics over the weekend.

I have seen/read a little bit about the tectonic-forcing mechanism idea for some caldera-style eruptions. The biggest thing to keep in mind is that the caldera-forming event – that is to say the collapse of the roof into the chamber – isn’t usually the “trigger” as much as a result of a large eruption that is already occurring. The roof collapse just finishes the job that has already started – I guess you could imagine it as hitting the afterburners of an already “lit” eruption. However, the question of the connection between the tectonic setting and eruptive activity is fascinating. You just have to be careful not to compare apples (Andean calderas) and oranges (Yellowstone) – although they’re both calderas, they are results of very different magmatic processes and tectonic settings.

As for Lazufre, I know that there has been some earlier articles (such as Pritchard and Simon, 2002 in Nature) that suggested that many of the Andean volcanoes are inflating and deflating regularly – the question here is whether this is all “normal” volcano behavior or just the result of us (humans) being able to notice this type of information for the first time. INSAR imaging on volcanoes has only really been utilized over the last 10-15 years.

Some news:

  • As many of you pointed out, there has been a lot of articles on the distribution of stimulus money to the various USGS volcano observatories. HVO, CVO, YVO, AVO and even the Northern Marianas will get new equipment to replace the aging infrastructure.
    The breakdown looks like this:

    • $950,000 for the Yellowstone Volcano Observatory
    • $7.56 million for the Alaska Volcano Observatory
    • $2.4 million for the Cascades Volcano Observatory in Washington state
    • $3.3 million for the Hawaiian Volcano Observatory
    • $200,000 for the Long Valley Observatory in California
    • $800,000 for upgrading networks in the CNMI – northern Marianas
  • There has also been a lot of press on the so-called “spiders” being installed at Mt. Saint Helens to monitor activity. I covered this briefly back in May, but I’m glad to see that people might be interested in volcano monitoring.
  • We have some details on the changes at Kasatochi in the Aleutians. As I mentioned a few weeks ago, an expedition was set to visit the island for the first time since last summer’s eruption. They will be heading out there this week with a reporter from the Anchorage Daily News and he notes that Kasatochi increased in size 32% thanks to the deposits from the eruption – how long that added material will last with the ocean fighting to take that space back is another question. I do love the sort of dry wit scientists partake in, such as this gem from the ADN article:

    In a science report in which they wrapped up their 2008 field season, biologists Ray Buchheit and Chris Ford wrote, under a section titled Interesting Observations, “Our island blew up.”

    Indeed it did!
    It will be fascinating to see what else they discover on the island that went from being a home for 200,000 auklets to a barren ash wasteland.

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Comments

  1. #1 mike don
    August 17, 2009

    You know, these two biologists on Kasatochi had a helluva narrow escape; sitting on a small island volcano in the midst of a major earthquake swarm, including bouts of tremor strong enough to feel, with miles of choppy ocean between them and safety and only a small inshore skiff to escape on. If that fishing boat hadn’t been able to pick them up (and with Aleutian weather that could well have happened) their chances would have been slim indeed. It should have been a major news story beyond Alaska

  2. #2 Thomas Donlon
    August 17, 2009

    An email list I am on posted this – and I am reposting it (minus the email addresses). Several people here have been discussing Taupo Volcanic region from time to time – I don’t know much about it and though I’d love to go – I certainly can’t afford it now!.

    ——————————————————-
    Dear all,

    The Student Chapter at CODES, University of Tasmania, Australia is organising the 1-week “Modern Concepts in Physical Volcanology Workshop” the 26-30 October 2009.
    Prof. Colin Wilson (U. Victoria, NZ) will be the main speaker (invited), with extensive contributions from Prof. Jocelyn McPhie, Dr. Sharon Allen, Prof. Dave Cooke, Prof. Ross Large, Prof. Bruce Gemmell, Prof. Tony Crawford and Dr. Emily Johnson (all at CODES, U. Tasmania).

    The workshop is opened to anyone interested to complete his/her knowledge in volcanology, but particularly adapted to postgraduate student level. A very reasonable registration fee is asked. The limit is put at 30 participants.
    Registration deadline: 15 September.
    The workshop is divided in several sessions:
    1. Introduction to volcanology
    2. Taupo Volcanic Zone and its eruptions as case studies of large-scale silicic magmatism and volcanism
    3. Volcanic flare-ups
    4. PDCs, ignimbrites and their eruptions- insights from case studies into pyroclastic flow emplacement and ignimbrite construction
    5. Subaqueous volcanism
    6. Alteration of volcanic rocks in VHMS, epithermal and porphyry systems.
    Discussions fill follow every session.

    For further information and registration, please visit:
    http://www.geol.utas.edu.au/studentchapter/index.htm
    Direct link : http://www.geol.utas.edu.au/studentchapter/090817%20Program%20and%20registration%20Workshop%20October%2009.pdf

  3. #3 Thomas Donlon
    August 18, 2009

    A year or so an expensive ten year study was done (it cost less than a tenth of the top baseball player’s yearly salary) – and they modeled a magma plume under Yellowstone that “rises to 75 miles below the caldera, where it hits cooler rock and spreads out to a width of 300 miles.”
    http://www.yubanet.com/cgi-bin/artman/exec/view.cgi/57/52083

    http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2009kkcw.php
    Now, I am wondering how close does an earthquake have to be to Rabaul in order in order for us to wonder if there is a volcanic element to such a quake.
    The quake above “130 km (80 miles) SE of Rabaul, New Britain, PNG”
    at a depth of “33.3 km (20.7 miles)” – might be within range of a magma plume if one exists?

    Now, if Yellowstone in the US just got imaged at depth a couple years ago – I am certain that no such project has taken place at Rabaul or most other volcanoes in the world.
    So connections between farther away earthquakes and volcanoes will remain speculative.

    I’ve got a question. If Yellowstone has a deep magma plume feeding the magma chamber that is a few miles down – do arc volcanoes near subduction zones have a deeper magma collection at a depth similar to the 75 mile deep Yellowstone one? I understand Yellowstone’s plume comes from deep, deep in the earth and an arc system is fed by a complex arrangement of magma and vapors rising from previously subducted material. At what depth does a subducted oceanic plate become a source for rising, buoyant volcanic magma? How deep does it have to go – and what starts rising, rocks melted by steam from deaper yet? Does water being released due to metamorphic changes in rock structure (chemical changes in subducting, pressurizing, baking rocks release H20 atoms) come up and boil and melt more surface rocks into lava?

    I’ll try to do my own studying. This is a big field and it is probably to time consuming to explain most or even many facets of these questions.

  4. #4 Erik Klemetti
    August 18, 2009

    Thomas – Those are great questions and heck, I’ve spent entire semester-long classes on the subject. I would try to answer them, but again, it would take me a text book. If you’re looking for a good book on the subject that isn’t too overly technical (although it is still a geology textbook), you might try Igneous Petrogenesis by M. Wilson. It is a little hard to come by, but it covers a lot of your questions. The long-and-short is that the geometry and structure of the magma sources for Yellowstone vs. an arc are very different, albeit both fundamentally drawn from mantle melting/upwelling.

    As for Rabaul, I would be surprised if earthquakes like the one you mentioned was directly related to any magmatism. Yellowstone is a BIG hotspot system in the middle of a plate and Rabaul is not, so although the quakes might be nearby, there is so much active tectonism in the area that deconvolving the source in the same way you could Yellowstone is problematic at best.

  5. #5 Thomas Donlon
    August 18, 2009

    Erik,
    I will see if I can find the book at a local library.

    I have given the following free online book a quick read before – not that I remembered many specifics. Maybe I will check that out again.
    http://www.geo.cornell.edu/geology/classes/geo455/Chapters.HTML

    I suppose that the one question I would like to have answered is this. -

    What is the minimum depth that something like an oceanic plate has to subduct in order to produce magma? Or what is depth at which whatever kicks off magma formation starts? The numbers certainly don’t need to be precise and will depend on the nature of the rock being melted etc.

    a) 12 miles?,
    b) 30 miles?
    c) 100 miles?
    d) 200 miles?
    e) even deeper?

    Erik, also Re: Rabaul you are certainly right – the whole area is seismically active. The more earthquakes there are near a volcano – the more I will ponder whether it will erupt.

    This little 4.9 quake I pointed to 80 miles from Rabaul wasn’t to suggest that anything different is going to happen there. If anything it might just be related to the light eruption that has been taking place there. If there was a nine magnitude quake in that area – I’d watch Rabaul carefully. If the 4.9 happened within the caldera itself – I’d be concerned about the safety of a local population in the event of an eruption.

    Most of the earthquakes around the ring of fire aren’t far from a volcano. If I had the locations of more volcanoes memorized, I’d probably spend more time watching larger quakes for any affects they have on nearby volcanoes.

  6. #6 Bruce
    August 19, 2009

    Erik, thanks for that book suggestion! Man, do I have some reading to do!!

    Thomas, you and I both seem to be on the same level, suffering the handicap of not having had the opportunity to study this stuff at university, so from one layman to another, one of the things that opened up my eyes in regard to the complexities of melt from a subducting plate was some seismic mapping of the Taupo volcanic zone. This radically changed my view of volanoes merely being the surface expression of a blob of magma sitting in a nice circular chamber in the crust. The map I saw was very convoluted and I suddenly realized there is melt of varying degrees in all sorts of places, sometimes pooling, sometimes spreading out in sills, some in neighboring pockets, some cooling off into solid granite, some in a state of crystal mush, etc. etc., some rising rapidly and so on.
    I suspect that in most active arc settings the real situation is kind of like a sponge where the sponge is crust and the interstices are melt with the added feature that the sponge is hard and cracked with faults running all through it.
    So, after that long rant, to get back to your original question, the answer, as I understand it, is “it depends”.Chaiten for example is very close to the plate boundary (implying either the plate is diving extremely steeply or that the melt is from a shallow source. I guess it is the latter because there is a MOR ridge getting subducted just to the south and I imagine this plays a role in the production of the melt feeding Chaiten.)
    The other variable affecting the depth of melt is obviously the chemistry of the rocks and at what temperature they melt. So, my 2c is that it is all exceedingly complex! Does that help?

  7. #7 Thomas Donlon
    August 19, 2009

    Hi Bruce,

    I looked up what a MOR ridge was. It is a Mid-Oceanic Ridge.

    So the ridge is continuing to send magma upward, even while being subducted under South America. Quite interesting!

    Your description is quite picturesque of the magma seeping through cracks, going every which way.

    Bruce, I think I will have to work through this question on my own – read some books – do searches on the internet. Probably in the time it takes to describe the question and get an answer – I could probably find the answer on the web. Let’s see its 7:44 – and I am off to find the answer. Tick tock, tick tock …
    7:52 I might have an answer in this abstract.
    http://www.agu.org/pubs/crossref/2001/2000GL012558.shtml

    It reads,
    “The assumption that the source of magma for volcanoes in subduction zones is located in the mantle immediately above the top of the subducting slab, at approximately 100 km depth and straight beneath the volcanoes is incorrect in northeastern Japan. The combination of evidence from velocity tomography in the mantle wedge above the slab and mapping of earthquake size distribution within it strongly points to a source of fluids at the top of the slab at 140 to 150 km depth, from where material rises along an inclined path to the volcanoes.”

    I am not sure that I am interpreting the abstract correctly, but the depth of 100km to 150km could be a depth at which magma or its heat source in the form of hot fluids comes from.

    Time to switch gears and do some chores around the house. :)

  8. #8 Bruce
    August 20, 2009

    Thomas, ha! I am impressed by your research skills! There is a good textbook I have which unfortunately is in German, I don’t know if there is an English translation available:

    Vulkanismus by Hans-Ulrich Schmincke

    He has a whole chapter on the genesis of magma, showing the pressure and temperature curves. Here’s a quote from it:

    There are basically three different processes (i.e. changes in the starting conditions) which can lead to the partial melt of solid rock and they are:
    * increasing temperature (pressure (P) and chemical composition (X) constant)
    * decreasing pressure (T and X constant)
    * change in X (P and T constant)

    so in other words, magma can originate at relatively shallow levels where the pressure is not so high but deep enough to display a high enough temperature.

    (any professionals who read this must be grinning at us stabbing around in the dark here but I am grateful to find somewhere online where I can even discuss this stuff with someone. My wife is not the least bit interested !)

  9. #9 Boris Behncke
    August 20, 2009

    There is indeed an English version of Schmincke’s book, entitled “Volcanism” and issued by Springer in 2004. This represents a much updated version of the German original (1998) book that Bruce cited. You may find some information here at Amazon:

    http://www.amazon.com/Volcanism-Hans-Ulrich-Schmincke/dp/3540436502/ref=sr_1_1?ie=UTF8&s=books&qid=1250753557&sr=8-1

  10. #10 mike don
    August 20, 2009

    Bruce: it seems to me that in a (very) general way the three processes correspond to the three main settings for volcanism:
    Increasing temperature (hot-spots)
    Decreasing pressure (rift systems/crustal extension)
    Compositional change (subduction zones with water and alkalis acting as a flux) Would that seem reasonable?

  11. #11 Bruce
    August 20, 2009

    Hi Mike, I never thought of that but I guess in a broad way you are quite right. Of course there would be a bit of each factor in every eruption but on a broad scale, sounds good to me! Would be interesting to hear what one of the experts here have to say on it!

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