Eruptions

Chaiten update for 2009

It is hard to believe that the eruption at seem to come out of nowhere at Chaiten started over 8 months ago now, and apparently is still not showing many signs of abating. I did get a chance to see some great talks and posters at AGU last month about the Chaiten eruption, with the key points I took away being that Chaiten is erupting a very crystal poor rhyolite (<1% crystals) and that it seems that the source of the magma is relatively deep in the Andean crust. Also, there are some indications that the eruption at Chaiten may have been tectonically instigated – i.e., that earthquakes in the area might have helped the magma to erupt – at least that is what Luis Lara of the SERNAGEOMIN believes (hat tip to Thomas Donlon for the link). The eruption at Chaiten also wreaked more havoc on aviation in South America than we thought, effecting airports 1000s of kilometers away and almost bringing down a number of aircraft. Most everyone I talked to seems to think what we are seeing is very similar to what happened at Little Glass Mountain in California about 1,000 years ago.

Moreover, the eruption hasn’t really stopped since it began in May of 2008. In fact, just last week we saw a collapse of part of the new dome that have produced some pyroclastic flows within and outside the caldera (see above and the Volcanism Blog) and fed more ash into the choked rivers near the volcano. It is anyone’s guess (well, at least at AGU) how long this eruption might go on – weeks? months? years? – but the consensus is that this might be a once-in-a-lifetime eruption (but we already knew that, didn’t we?)

Comments

  1. #1 Bruce
    January 25, 2009

    Interesting stuff Erik, so
    1. does crystal-poor imply relatively hot and/or high pressure conditions for the magma and therefore rapid ascent from depth?

    2. Would this rule out any possibility of a large caldera-forming eruption (assuming that such eruptions only occur when a large relatively shallow magma chamber erupts)?

  2. #2 Bruce
    January 25, 2009

    Sorry, just read one of the abstracts which effectively answers my first question, which leaves q2.. do you get large caldera forming eruptions from deep sources like this?

  3. #3 Erik Klemetti
    January 25, 2009

    Bruce – I don’t think we have a good idea of that exactly the effect of a deep source might be on the chances of a caldera-forming eruption. However, we know that Chaiten has had a caldera-former before, so unless the processes that form the magma at Chaiten has changed dramatically since that time, it isn’t out of the question.

  4. #4 Ross
    January 25, 2009

    A little off topic here but looks like things might be heating up at Redoubt.
    Check out AVO’s site:
    http://www.avo.alaska.edu/activity/Redoubt.php

  5. #5 rafael peralta
    January 25, 2009

    Have not read the abstracts yet, but a tectonic cause has been in my agenda for long. Other points of interest in the agenda are:
    1.- The eruption is part of a process of tectonic “accomodation” going on since May 21st 1960. It should involve other volcanoes along the Liquiñe Fault. It has involved so far two Major earthquakes (1974 and 1975), the 1991 Hudson eruption (VEI 5), the Aysen fjord swarm.
    2.- The Chaiten eruption is a “vent” eruption from the Michimahuida Volcano a few miles northeast. (Deep magma, lots of water from melting ice or from sea basin)
    Regards from the Nazca Plate Subuction Zone!

  6. #6 rafael peralta
    January 25, 2009

    Just read one of the abstracts (Lara, Pallister et al) and the word “compression” appears several times… QUOTE: “We propose a model for magmatism at Chaitén, in which the timing and compositions of eruptions are controlled by tectonism along the Liquiñe-Ofqui Fault Zone (LOFZ), a 1200 km long structure that is part of a dextral transpressional arc domain. In this model, silicic magmas are trapped and stored at deep levels of the crust (10 km?) during periods of upper crustal localized compression, and eruptions are triggered by tectonic shifts that open tear faults and promote magma transport to the surface. Consistent with seismicity along the LOFZ and subsidiary branches before and during the eruption and with new InSAR data that indicate fault-controlled syn-eruptive deformation, we suggest that such a process triggered the 2008 eruption and that re-establishment of compression, following the initial Plinian phase, has sustained an anomalously high-rate of lava production for the past four months. ”
    Dr. Klementi, Do you remember your doubt in previous “Is Chaiten a clogged Volcano” entry? QUOTE: “Technically, I’d be surprised if compressional movement would cause volcanism as typically one associates volcanism with extensional movement.” Technically it has been answered.

  7. #7 Erik Klemetti
    January 25, 2009

    Well, I’ll tell you I was surprised by Dr. Lara’s conclusions, but Chaiten is definitely in a unique tectonic setting. There are a lot of complex geometries at play around that part of the southern Andes, so the storage and eruption of silicic magmas due to these forces might be most apparently near Chaiten and volcanoes around it. Sounds like there will be a lot of work to be done to examine this interplay of tectonism and magmatism.

  8. #8 Beano
    January 25, 2009

    There are a whole string of Volcanoes sited along the Sumatera fault in Indonesia. Krakatau lies above a sharp bend in the border of two subduction plates.
    Anecdotally, the local people on Nias island just off Sumatera and mainland people tell of an earthqake and tsunami around 1880. There is also anecdotal talk of a earthquake on the Sumateran Fault on the island not long after. Again there is evidence and anecdotal knowledge of at least one Sumateran Volcano (Sibayak) not long after this (1881). Sibayak is very close to the run of the Sumateran fault line. And of course in 1883 Krakatau.
    I know that Mike Rampino has suggested that the Krakatau eruption might be linked to a tectonic event. He had some evidence of this.

    Interestingly the people of Nias Island have handed down knowledge that tells them to run for the hills after a major earthquake in case of a Tsunami. Also interestingly the fatality level on Nias was very small compared to the west coast of Aceh after the Dec 2004 Mag 9.0

  9. #9 Bruce
    January 26, 2009

    Sometimes I think the term caldera is misused.. I mean you have calderas like Yellowstone, Long Vallley, Toba, Taupo and so on, and then you have calderas like Chaiten, Tambora, Pinatubo.. which although mighty eruptions look more to me like the hole left when you blow the top off a mountain as opposed to the first calderas that are formed by collapse in on an empty magma chamber.. How would you rate Chaiten’s caldera in this regard? Was it formed by collapse in on a shallow magma chamber or is it just the superficial hole after an explosive eruption?

    Re the compressional / extensional thing.. what are the mechanics of rising magma.. (this gets back to a question I have long had) .. does the magma rise due to a combination of heat and buoyancy, melting the rocks above it and finding suitable cracks/faults to move upwards and if so, wouldn’t faulting play a major role? What is the geochemistry of rocks on a fault line.. a friend once described them as silly putty.. under great stress already and every now and again snapping… couldn’t the addition of heat from below cause a sudden phase change in rocks that were already close to snapping and therefore encourage upwards movement of magma? The extensional thing explains larger scale bodies like the TVZ because the crust is so thin but faulting is obviously at play locally as Tarawera and Taupo both show (Taupo erupted on a line of vents approx. 50 km long, Tarawera similarly though on a much smaller scale.

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