UPDATE 2/19/2009 9:45 AM: Well, it seems that my hunch was at least partially right. Reuters (and Paula Narvaez, special envoy to the Chilean president) is calling the eruption as result of "what appeared to be a partial collapse of its cone."Â So, we might have seen the oversteepening of the dome growing in the Chaiten caldera that lead to a collapse, producing (likely) a pyroclastic flow and either an accompanying plinian eruption as the pressure was released or an ash column associated with the pyroclastic flow itself. Now, I might not take Reuters word for it, but it makes sense considering the suddenness of the event.
10:00 AM: More details for Reuters, including the ominous "Our security team have observed an increase in the size of a column of ash and smoke, with a deformation to one side" from the Deputy Interior Minister. My guess is he is referring to deformation on the ash column, not the volcano.
4:00 PM: From a Newsday article, just some more details on the ash dispersal: "On Thursday, increased seismic activity was reported and ash fell 100 miles (160 kilometers) away in Futaleufu."
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Eruptions reader Brian Owens has pointed out that fellow volcano follower, the Volcanism Blog, is reporting that Chaiten is experience a major rejuvenation today.
Sure enough, the Associated Press also reporting that an explosion has occurred in the main dome of Chaiten that has been built since last May and that material is moving downslope from the explosion. There is no clear word what type of volcanigenic material this might be - pyroclastic flow, lahars, avalanche - but there is a major fear that it could block the river and cause flooding in the town of Chaiten. The few citizens left in the area are being evacuated. The Patagonia Times adds that the eruption started around 11 A.M. (local time) and ash has spread across much of the region.
From what I can gather, this seems like it might have been either a dome collapse that was quickly followed by an explosion (possibly caused by the release of pressure from the collapse) or some "burp" of gas-rich magma erupting. The reports of "a massive column of ash" are interesting as this could suggest a true new flux of magma, but it is hard to tell at this point how widespread is the ash and how tall the column might be. At this point, it is all conjecture, but it sounds like Chaiten might be making a comeback. The questions woulds be how big and for how long.
I'll update as we find out more ...
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Erik, if this was a partial dome collapse, does this relieve some of the pressure that had been building up, and therefore lessen the chances of a huge eruption? I would think that the dome buidling process would still go on, but maybe at a faster pace since there is less pressure to inhibit it?
Brian -- It is hard to say that the two are so closely linked. For the short term, it might alleviate pressure, but I don't think a dome collapse would have much effect on the long term prospects of eruption at a given volcano.
I post the same post here that I posted on the Volcanism Blog, which is as follows:
What we see in the webcam image is clearly the nose of a pyroclastic flow ... the amazing thing is that it has travelled quite close to the town. It seems that there has been a large dome collapse event, so it would not be exactly accurate to speak of a new eruption or reactivation, fact is that it has been active all the time, even though at fluctuating rates. Later web cam images (at 19 h GMT on 19 February) show a fresh, fuming pyroclastic flow deposit in the gorge through which the flow travelled. Looking at this, maybe those who were sceptic about the decision to relocate the town of Chaitén permanently will understand ...
To respond to Brian Owens' question above, I agree with Erik, the collapse of a part of a lava dome does not have any effect on the future course of the eruption. Sometimes, smaller dome collapses precede much bigger ones by hours to days, as has been seen at Unzen (Japan) in the early 1990s and at Soufrière Hills (Montserrat) a few years later. So, I would rather say that these events show how correct the decision made by the Chilean Government to permanently relocate Chaitén town has been.
Looking at the current webcam pictures it looks like there may have been another pyroclastic flow starting at the 16:52 photo. You can see a darker ash cloud coming from the obscured volcano then moving into the valley in the images thereafter. (The last 3 images as of this post)
The webcam slide-show shows that there have been several collapses and/or small explosions through the afternoon.
The live cam is incredible. The person controlling it just zoomed in to the volcano's peak. Thick steam and ash is billowing out. There still appears to be a tall spine farther north on the dome.
Here's a link to the live cam that opens in windows media player.
http://wms01.mediastream.cl/chaiten
With reported light ash fall in Futufula would not this indicate an eruption along with a dome collapse?
There might have been some Plinian component to the event that would account for the ash dispersal. As mentioned above, in the short term, a dome collapse can allow for a release of pressure that sparks a proper eruption. Remember, to get oversteepening, you still need to be pushing magma up from below the dome!
I guess Chaiten got sick of waiting for Redoubt to do something, eh?
Hi Erik,
Great coverage of today's events at Chaiten. Just to clarify for non-specialists, the phrase "Plinian component" may not be the right one here, unless you can show there was a sustained vertical column of ash/pumice that reached altitudes >20 km (Plinian refers to an eruption style and magnitude or volume a la G.P.L. Walker and like Chaiten in May 2008). I think i know what you mean though, that there may have been vesiculation and fragmentation of new magma apart from that which formed the block and ash flows, or pfs...
My guess (from the lazyboy) is that the excess ash was associated with "vulcanian" activity (a rapid decompression and fragmentation event) due to unloading of the dome and expulsion of shallow bubbly magma, as has happened recently in Soufrière Hills.
My sister and her husband started a backpacking trip yesterday in the area. She only stated they would be in a National Park area known for its "lakes". She may have even said the Lake Region. I am assuming this is the area. Are they in any danger? Is anyone checking on trekkers in the area? Any ideas on who to contact?
Thanks for any help.
Lisa
Thanks for the clarification, Jonathan. I can play a little loose-and-fancy-free with some of my terminology, which is a bad habit. I think this reminds me that I need a refresher on the proper usage of volcanic terms (look for this in the near future).
Lisa - It would really depend on exactly where they are in the area. I would hope they couldn't get too close the Chaiten without the authorities in Chile stopping them. If you're worried, I would contact the US Embassy in Chile and go from there. They would know best who to talk to in the country if you are worried.
Hi Erik,
Thanks for posting the figure showing the different modes of eruption. It's very helpful and clears some cob-webs in my own memory!
cheers, Jonathan