Eruptions

A few weeks ago I asked you to submit questions on the 2008-present Chaiten eruption in Chile to pose to Dr. Jonathan Castro. Dr. Castro recently had a paper on the ascent rates of Chaiten rhyolite published in Nature and he kindly volunteered to answer your questions. Here are the answers to selected questions … enjoy!

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Chaiten in Chile erupting in 2009. Image by Dr. Jonathan Castro.

Dr. Jonathan Castro
Biography:
B.S. from Humboldt State University
Ph.D. from University of Oregon*
Currently a Research Geologist at CNRS-Institut for Sciences de la Terre, Oreans, France
Soon moving on to Monash University in Melbourne, Australia

* = EK Note: We can’t all be perfect.

Chaiten questions
(SHIRAKAWA Akira): As of today, approximately how much magma (in volume / km3) has been erupted from Chaiten Volcano since the start of its eruption in 2008?

JC: ALTHOUGH FIRM ESTIMATES ARE NOT YET AVAILABLE BECAUSE THE PROXIMAL (CLOSE-to-the-VENT) DEPOSITS HAVE NOT BEEN THOROUGHLY MAPPED, WATT ET AL. (2009) SUGGEST THE TEPHRA ACCUMULATION TO BE AT LEAST ~0.1 KM3, ALTHOUGH LARA (2009) NOTES THAT THE TOTAL COULD BE AS HIGH AS 4 KM3. WE WILL HAVE TO WAIT UNTIL THE DEPOSITS ARE MAPPED TO GET A FIRM ESTIMATE. IT IS ALSO IMPORTANT TO NOTE THAT THE REGION MAY RECEIVE UP TO 5 M OF RAIN PER YEAR, WHICH WILL HAVE WASHED AWAY A LOT OF MATERIAL.

Citation: Watt, S. F. L., D. M. Pyle, T. A. Mather, R. S. Martin, and N. E. Matthews (2009), Fallout and distribution of volcanic ash over Argentina following the May 2008 explosive eruption of Chaitén, Chile, J. Geophys. Res., 114, B04207, doi:10.1029/2008JB006219.

Citation: Lara, L.E. (2009) The 2008 eruption of the Chaiten volcano, Chile: a preliminary report, Andean Geology, vol. 36: 125-129.

(Lockwood DeWitt): Would seismic investigations allow volcanologists to identify magma chambers that might erupt in this manner? If seismic is impractical, are there any other techniques that might allow identification of such magma bodies?

JC: AS FAR AS I KNOW, SEISMIC STUDIES CAN TELL YOU THE APPROXIMATE POSITION OF A MAGMA BODY, BUT NOT THE COMPOSITION OR HOW IT IS GOING TO ERUPT.

(Barry Abel): The National Geographic article on the Chaiten finding is titled “Worst Volcanoes Even More Dangerous Than Feared”. It implies that Dr. Castro’s study means that large rhyolitic volcanoes such as Yellowstone can erupt with little warning. Until now, volcanologists have been saying that Yellowstone would give plenty of warning. Is the article ignoring the differences between calderas such as Yellowstone and mountains such as Chaiten, or are rhyolitic calderas really in danger of erupting with little warning?

JC: THE CASTRO AND DINGWELL ARTICLE DOES NOT ADDRESS THE BEHAVIOR OF BIG CALDERAS, WHICH MAY BE DIFFERENT DUE TO THE MASSIVE VOLUMES OF MATERIAL CAPABLE OF BEING PRODUCED IN CALDERA-FORMING ERUPTIONS. BUT BIG CALDERAS MAY ALSO PRODUCE MEDIUM OR SMALL SIZED ERUPTIONS, SO THAT MAKES OUR STUDY RELEVANT TO THE BEHAVIOR OF THESE SYSTEMS. THE FORMAT OF NATURE MAGAZINE PLACES STRICT LIMITS ON SPACE AND THEREFORE THE NUMBER OF IDEAS (JUST ONE) THAT CAN BE CONVEYED.

(Dr. Aldo Piombino): Certenly it could be interesting drawing some characteristic of the Chaiten lava vs. the lavas of other ryolithic domes for understanding whether Chaiten dome is the very rule or is an exception.
And what about the situation of the underlying magma chamber? Is this the product of a crustal anatexis due to a deeper basaltic magma rise or not?

JC: “RULES” ARE HARD TO DEFINE WHEN DEALING WITH VOLCANOES, AS EACH HAS ITS OWN UNIQUE HISTORY, DICTATED BY THE PHYSICS AND CHEMISTRY OF THE MAGMA SYSTEM (NOT TO MENTION THE OVERLYING CRUSTAL STRUCTURE). THERE ARE STILL SIMILARITIES BETWEEN SYSTEMS, LIKE THE WAY ACTIVITY DURING ONE EPISODE MAY CHANGE WITH TIME (COMMONLY STARTING EXPLOSIVE THEN GOING EFFUSIVE). WE CAN LEARN A LOT BY “WATCHING” VOLCANOES ERUPT, BUT, IN THE CASE OF EXPLOSIVELY ERUPTING RHYOLITES, WE HAVE JUST 1 INSTANCE WHERE THIS WAS POSSIBLE. THERE’S NO EVIDENCE OF A BASALTIC INPUT OR TRIGGER TO THE ERUPTION. BUT THE CRYSTALS WE STUDIED SHOW SOME EVIDENCE THAT THEY WERE CHEMICALLY AND/OR THERMALLY PERTURBED BEFORE THE ERUPTION.

THE ORIGIN OF RHYOLITE MAGMA REMAINS AN ACTIVE AREA OF RESEARCH. COMPETING IDEAS INCLUDE THE “ANATEXIS” (PARTIAL MELTING) MODEL YOU MENTION, AND ALSO EXTENSIVE CHEMICAL DIFFERENTIATION OF MORE PRIMITIVE MAGMAS. IN THE CASE OF CHAITEN WE DO NOT KNOW WHICH APPLIES. MAYBE ERIK CAN CHIME IN?

Erik (chiming in): The generation of rhyolite is definitely going to vary based on the specific location of the volcano – mostly controlled by the heat source/flux, the density of the overlying crust (allowing for stalling) and the previous magmatism in the area. However, even though Yellowstone and Chaiten might be very different in their setting, the overall generation of rhyolite liquid could be similar in the basic sense. I also want to mention that a third possible source for rhyolite beyond crustal melting and differentiation might be crystal cumulate reactivation (melting), which is sort of a hybrid of the two JC mentioned.

(Bruce Stout): Why is Chaiten so close to the coast (and presumably the plate margin)? Presuming there is a magma chamber at 5 km depth, how big do you expect it to be? If the magma was erupted rapidly from a depth of 5 km, how long do you think it spent at that depth before erupting? Do you suspect a deeper source that is feeding the chamber at 5 km depth? Is the magma from Chaiten high or low in volatiles? What do you think the likely scenario is for the future of Chaiten?

JC: CHAITEN IS IN A “NORMAL” POSITION WITHIN A VOLCANIC ARC, MEANING THAT IT IS LOCATED AMONGST MANY OTHER VOLCANOES THAT DEFINE THE SOUTHERN CHILE VOLCANIC ZONE. THE “TRENCH” OR PLATE BOUNDARY IS ACTUALLY QUITE FAR TO THE WEST OF CHAITEN (>200 KM). THIS SUBDUCTION ZONE ARC IS THE PRODUCT OF MELTING PROCESSES TAKING PLACE SOME 60-170 KM BENEATH THE CURRENT ARC POSITION (SEE ALSO GROVE ET AL 2009).

CITATION: T. L. Grove, C. B. Till, E. Lev, N. Chatterjee, E. Médard (2009) Kinematic variables and water transport control the formation and location of arc volcanoes, Nature 460, 1044-1044 (20 August 2009) doi:10.1038/nature08312

WE DON’T KNOW, NOR CAN WE PREDICT THE SIZE OF THE MAGMA CHAMBER UNDER CHAITEN. MAYBE A SEISMIC TOMOGRAPHY STUDY COULD ELUCIDATE THIS.

WE DON’T KNOW HOW LONG THE MAGMA SAT IN THE CHAMBER BEFORE ERUPTING. ERIK KLEMETTI IS THE “GURU” AT THIS SORT OF WORK (EK note: Well, I wouldn’t say that) AND WE HAVE BEGUN DISCUSSING THIS AS A TOPIC OF FUTURE WORK. IT IS CLEAR THAT THE MAGMA WAS NOT IN A “STEADY STATE” BEFORE ERUPTING BECAUSE MANY OF THE FELDSPAR CRYSTALS APPEAR TO HAVE BEEN UNSTABLE IN THE MAGMA CHAMBER.

DEEPER SOURCE, YES IT IS QUITE POSSIBLE. OUR RESULTS GIVE A UPPER BOUND OR THE SHALLOWEST POSITION OF THE CHAMBER.
THE MAGMA AT CHAITEN IS H2O-RICH, LIKE MANY OTHER SILICIC MAGMAS IN ARCS.

RHYOLITE LAVA DOMES CAN GROW TO VERY LARGE SIZE (SEVERAL KM3). I WOULD NOT BE SURPRISED IF THIS CURRENTLY GROWING DOME(S) CONTINUE THAT WAY FOR A LONG TIME.

(R. Fitzpatrick): What do you think is the cause of the magma moving faster? Has it gotten thicker/thinner, become more or less viscous, is it under greater pressure? Has the vent gotten larger or straighter?
Could the different rims that grow at different pressures act like blood platelets and affect the “coagulation” of the magma?

JC: WELL, WHEN A MAGMA IS RICH IN WATER, ITS VISCOSITY WILL BE REDUCED BY SEVERAL ORDERS OF MAGNITUDE, TRANSLATING TO AN EASIER ABILITY TO FLOW. ANOTHER THING THAT FOSTERS THE RAPID FLOW IS THE LACK OF CRYSTALS IN THE MELT, WHICH WOULD INCREASE THE VISCOSITY GREATLY. IT IS INTERESTING THAT THIS ERUPTION OCCUPIED THE SAME VENT AS THE PREVIOUS ONE. MANY RHYOLITE SYSTEMS OF SIMILAR SIZE FORM CHAINS OF DOMES (LIKE AT S. SISTER VOCLANO OR THE INYO DOMES) RATHER THAN A POINT. COULD THIS HAPPEN AT CHAITEN?

(Thomas Donlon): Have any recent analysis been done on Chaiten ash / eruptive material – and if so – does this indicate any change possible for the Chaiten eruption?

JC: AS FAR AS I KNOW, THERE IS NO EVIDENCE OF A CHANGE IN MAGMA COMPOSITION FROM LATER ERUPTED ASH.

(Guillermo Ebensperger): In the case of Chaitén (or the rhyolite volcanoes in general, if it is the case), why, if the magma is too viscous, they are continuinally erupting for a very long time? Is because of the magma’ speed or there is a relationship with the magma chamber size?

JC: MAGMA MAY ERUPT FOR A LONG TIME IF THE FORCES DRIVING THE MAGMA UP AND OUT OF THE CHAMBER (OVERPRESSURE AND BOUYANCY) PERSIST AND IF THERE IS A BIG SUPPLY OF FRESH MAGMA.

(Erik): Are there any other volcanoes/volcanic eruptions that you know of that are similar to Chaitén in its style and nature? Are there any particular systems that might not be on everyone’s radar that you might be concerned about in terms of potential activity?

JC: ONE THING THAT IS CLEAR FROM THE OLDER DEPOSITS IS THAT THEY TOO STARTED OFF EXPLOSIVELY AND THEN TRANSITIONED TO LAVA DOME/FLOW ACTIVITY. CHAITEN APPEARS TO HAVE BEEN A PARTICULARLY ENERGETIC ERUPTION COMPARED TO THE OTHER MEDIUM/SMALL SIZED RHYOLITE DEPOSITS I’VE WORKED ON (MEDICINE LAKE AND NEWBERRY). FOR EXAMPLE, THE TEPHRA DEPOSITS AT CHAITEN ARE VERY FINE GRAINED (LOTS OF ASH), EVEN CLOSE TO THE VENT, WHICH MEANS THE FRAGMENTATION MECHANISM WAS VERY EFFICIENT AND LIKELY DRIVEN BY VIGOROUS DEGASSING AT THE FRAGMENTATION LEVEL. THIS EXPLOSIVE DEGASSING, IN TURN, MAY HAVE BEEN PROMOTED BY FAST MAGMA RISE (NO TIME FOR THE MAGMA TO LOSE ITS GAS UNTIL VERY SHALLOW LEVELS). AT OTHER HOLOCENE OBSIDIAN SYSTEMS, THE PROXIMAL DEPOSITS ARE MUCH COARSER, WHICH MIGHT IMPLY A LESS EFFICIENT AND ENERGETIC FRAGMENTATION MECHAMISM.

GOOD QUESTION ABOUT OTHER SYSTEMS THAT MAY BE OFF THE RADAR! I BETTER TURN MINE ON! I HAVEN’T TRAVELLED THE WORLD IN SEARCH OF ALL THE OTHER POSSIBLY ACTIVE RHYOLITE SYSTEMS, UNFORTUNATELY.

Thanks again to Dr. Castro for fielding these questions! Chaiten looks like it will keep us captivated for years to come.

Comments

  1. #1 bruce stout
    October 26, 2009

    wow! Many, many thanks to Dr. Castro. Tell him I owe him a drink of his choice!

  2. #2 Ralph
    October 26, 2009

    This is really fascinating! Like all Chaiten-watchers I am very grateful to Dr Castro for taking the time to answer the questions and share his expertise, and to Dr Klemetti for putting this feature together. Many thanks, gentlemen.

  3. #3 Jonathan Castro
    October 26, 2009

    Hi Dr. Klemetti–Many thanks for moderating this Q&A session; you have really helped keep a spotlight on Chaiten. And, thanks to your readers, who have come up with some really insightful questions!

    Perhaps we could discuss crystal ages from Chaiten at AGU? I’ll even forgive the cheap shot about being ¨perfect¨, if you buy me a beer!

  4. #4 Boris Behncke
    October 26, 2009

    I must say this on-line scientific discussion with Dr Castro was a very good idea, thanks to himself for offering it and to Erik for providing the forum. There’s a lot of interesting information coming out this way, and I find rhyolite volcanic systems quite intriguing – also because we’ve got a few here in Italy (besides virtually any other geochemical suite to be found worldwide). The island of Lipari, one of the Aeolian Islands north of Sicily, is a rhyolite system, and it’s a historically active volcano, so the odds are it will erupt again some time – maybe in a few decades, maybe in a few millennia. The lessons from Chaitén are important here, because it’s a densely poplulated area, with enormous quantities of tourists visiting in the summer season.

    By the way, if anybody’s interested, I would be willing to do a similar Questions and Answers session about our Italian volcanoes here, especially Etna… let me know. These volcanoes haven’t been much in the news lately, which makes it all the more probable they will be back soon, most probably Etna, within less than a year I’d bet.

  5. #5 Fitz
    October 26, 2009

    Many Thanks to Dr Castro and Dr Klemetti.
    Just a quick follow up question. I can easily understand the rapid change in viscosity from changes to the crystalline structure of magma or partially melted rock, and how small changes of temperature would trigger it. Is there any mechanism that would increase the water content of rock at these depths in the time scale we’re looking at, ie between major eruptions?
    Thanks!

  6. #6 Thomas Donlon
    October 26, 2009

    Hi Fitz,

    I just put up an answer to your last question left in the last blog titled by Erik as -
    The return of the dreaded “giant magma chamber” of the Cascades.

    I hope my answer in the other blog comment will prove adequate.

    I’ll just give the briefest summary here.

    Certain rocks, when heated, change chemically releasing water in the process. The changed rocks are then called metamorphic rocks. That is where much of the water at depth comes from. Perhaps some water may just get dragged down by subduction as well.

  7. #7 bruce stout
    October 26, 2009

    Dr, Castro, you mention that the crystals you studied showed some sign of being chemically/thermically perturbed prior to eruption.
    1. Do you think this also a signal of whatever it is that triggered the eruption (and therefore perhaps a causal factor in other rhyolite eruptions)?
    2. What mechanism do you think could be responsible for this perturbation? Would this be heat influx from a deeper source or because differentiation in the magma chamber crossed some critical threshold or something along those lines?

    And once again, thanks to both you and Erik for getting the chance to do this. It really is unique. And Boris! I’d jump at the chance!!

  8. #8 Sightseer
    October 27, 2009

    Excellent posts!! I find geothermal activity particularly fascinating. When I was in Yellowstone not long ago, geothermal pools were awesome! Do you believe the theories that there will be a supervolcano in Yellowstone?

  9. #9 Robert Brossfield
    October 27, 2009

    As a lodge “owners” in the Chaiten area, we are really thankful for such information as we must determine when and if it is safe to re-open. Having been in Chaiten for the February 18, 2009 re-eruption/evacuation, I can tell you that the people of the region want science based opinions on when and how to re-occupy the region proximal to the volcano. That is doubly important to us as we bring tourists into the region.

  10. #10 Jonathan Castro
    October 27, 2009

    To Bruce–

    We are looking into this problem of the feldspars being unstable in the melt prior to eruption by running more experiments. It is too soon to tell for sure what was the cause, although adding heat would certainly do it, or redissolving some of the water that was held in bubbles whilst the magma was stored could have the same effect. Redissolving water requires a pressure increase on the system, or perhaps another volatile agent, like CO2, fluxing through the system, but either of these mechanisms will be hard to prove. Thermal input could indeed be caused by another hotter magma entering the chamber. But it is also possible to heat things up through crystallization (latent heat) or by shearing the magma intensely, as happens during ascent to the surface.

    As far as this being a ¨signal¨ of the trigger, that question will be even harder to answer convincingly than what caused the crystals to appear unstable.

    jc

  11. #11 Aldo Piombino
    October 27, 2009

    yhank you for this discussion. It is one of the most interesting discussions in the net, this year.
    For Boris, I’m really interersted in italian volcanoes (naturally!)

  12. #12 bruce stout
    October 28, 2009

    Dr. Castro, have I understood that correctly? Redissolution of the water would also decrease the viscosity of the magma and thus facilitate rapid ascent. Is that right?
    If so, could this pressure increase possibly have come from seismic activity? And again, if that were possible, what kind of timeframe would be required for this?

  13. #13 Karl E.
    October 29, 2009

    Dr. Klemetti,

    I asked some very broad questions of Dr. Calastro. Perhaps they were much too broad, but given my profession, and my background, they were questions that interested me deeply: in every field of science there are obstacles or road-blocks to advancement. I am always curious when someone has navigated around them. The first thing I have observed in individuals who have successfully advanced their field, is this: that they have a ready awareness of the obstacles. The second thing I have observed is this: that they have considered many paths around those obstacles and that they have identified the best paths currently open to them and, most interestingly, they have identified better paths that might soon become available to them. I realize that my questions have been broad, perhaps hopelessly broad and unanswerably broad. I apologize for my curiosity, but to ask the questions is hard to resist.

    Thank you.

  14. #14 Diego Olivares
    November 15, 2009

    Hello Mr. Castro, Mi nombre es Diego y estoy haciendo un proyecto para mi escuela (6Th grado)acerca de los volcanes, y yo escogi el volcan Chaiten. Quisiera saber de donde viene la palabra chaiten y cual es su significado?. Muchas gracias, Yo vivo en Estados Unidos y el nombre de mi escuela es Paul Revere Middle School.

  15. #15 Tomeka Yoshimura
    December 9, 2010

    I’m still learning from you, while I’m trying to reach my goals. I absolutely enjoy reading everything that is written on your site.Keep the information coming. I enjoyed it

  16. #16 cheap textbooks
    December 21, 2010

    Seriously? Is this post an attempt at a joke? I must be missing some thing here…

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