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The view from Chaitén, 22 February 2009 22 February 2009

Posted by admin in Chaitén, Chile, eruptions, volcano monitoring.
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This is the view from the DGAC camera at Chaitén airfield at 08:23 local time today. A significant plume can be seen, of whitish colouring indicating that it is mainly steam, blowing away to the east.

Chaiten 22 February 2009, 08.23

The following pictures are from the Tele13 webcam (direct link here, link that opens in your default media player here). The first, from yesterday evening at 20:27 local time, shows the tall and steep-sided pinnacle of extruded lava, the collapse of which has been predicted repeatedly over the last few days, still very much in place.

Chaiten 21 February 2009, 20.27

The last two pictures were captured by the Tele13 webcam in the early hours of this morning, and show incandescence atop the dome and the pinnacle, as fresh lava is constantly extruded.

Chaiten 22 February 2009, 03.24

Chaiten 22 February 2009, 03.27

For all our Chaitén coverage: Chaitén « The Volcanism Blog.

Information
Global Volcanism Program: Chaitén – summary information for Chaitén (1508-41)
SERNAGEOMIN – Servicio Nacional de Geología y Minería (Spanish)
Erupción del Volcán Chaitén – extensive coverage of the Chaitén eruption

The Volcanism Blog

Comments

1. Flemming - 22 February 2009

Unfortunately the same development as Tambora and Krakatau, first a preceding eruption, then a low-intense period followed by a new and more violent phase!

I hope I’am wrong, but this could be the start of more violent phase!?

Has the authorities a plan for that kind of event?

2. Volcanophile - 22 February 2009

The pinnacle looks quite high (I guesstimate it to be at least 350 meters high, referring to the width of the crater) and the flanks of the dome look incredibly oversteepened..

This seems to be a very unstable situation there at Chaitén.. The question is not whether it will collapse, but WHEN it will do so….

Time will tell..

3. Vicki Lansen - 22 February 2009

I am hoping that it’s not too ignorant to ask…but what accounts for “incandescence”…is it gas, or lava, or what?

4. Alan Sullivan - 23 February 2009

As I see it, this collapse is merely the inevitable consequence of gravity’s tug at the unstable pile of extruded lava. If the dome collapse were enough to release pressure and cause a bigger eruption, it would already have happened. But I have to wonder about the long-term trend. What do you think, Dr. Harrington? Do you see increased or diminished risk for a serious explosion, as the duration of activity and volume of the dome keep growing?

5. Arthur Meier - 23 February 2009
6. volcanism - 23 February 2009

It’s lava, Vicki, being extruded, cooling, and building up the dome, In the first of the overnight pictures there is an area of lava glowing in the centre; in the second picture, taken a few minutes later, the area of incandescence has been much reduced, as the lava cools and sets in place as part of the dome.

Chaiten seems to be in a steady-state situation at the moment. The rate of lava extrusion (a function of the rate at which magma is being introduced into the system at depth), the potential explosivity of the erupted material, and the rate at which small collapses happen often enough and at a sufficient speed to release the pressure that might otherwise build up to one big collapse, all seem to be in balance. A change in any one of the factors – new magma, a major blockage, a change in the composition of the magma – could change everything. A major explosion remains a possible outcome, and that dome can’t keep growing for ever – but the activity may decline and the growth stop with nothing catastrophic occurring.

Another point is that the discussions of Chaiten at the AGU in the autumn seemed to indicate, from the research of Luis Lara and others, that the Chaiten magma is coming from great depth and rising very fast, and that it has a tectonic origin. The eruption may well have been switched on at depth, and may be switched off at depth as well.

7. Salvatore - 23 February 2009

What about the large pinacle? That’s very unstable, clearly. Could that falling be enough to trigger a big collapse event? And this is a rhyolitic eruption, I understtood – doesn’t that mean explosive, not building a big mountain?

8. Boris Behncke - 23 February 2009

To answer Salvatore – the explosivity of an eruption does certainly depend, in part, on the chemical composition of the magma, and rhyolite is a composition typically linked to explosive eruptions. But there are other factors playing important roles also in determining whether such an eruption will be explosive or rather effusive (dome-building, in this case): gas (the gas that comes with the magma), and external water such as lakes, the sea, or groundwater. Gas, especially water vapor and carbon dioxide, make eruptions more explosive, and they can even make basaltic eruptions (rather fluid magma) astoundingly explosive, as we see often at Etna in Sicily. On the other hand, if there is little gas in a magma – no matter if it’s basalt or rhyolite – it will rather flow than explode. There are numerous spectacular examples of rhyolite lava domes and flows, such as in Long Valley, California (Mono Craters), Chao in northern Chile, and Rocche Rosse on Lipari, Italy. Some rhyolite lava flows are surprisingly long, but they also take exceptionally long to reach their full length – the Lipari example is known to have taken about 200 years to reach a length of little more than a kilometer. This has important implications – such eruptions seem to be capable of continuing for long periods, so maybe Chaitén is still only in its initial stage. I would rather expect to be the rest of this eruption predominantly lava extrusion with lesser explosive activity (besides decompression blasts triggered by dome collapse like last week), rather than building up toward a climax like Tambora, but with volcanoes you never know.
The pinnacle on the dome is indeed quite impressive, it seems to be bigger (not necessarily taller) than the famous spine that rose from Montagne Pelée in a later state of its devastating pyroclastic flow-producing eruptions in 1902. Not easy to say what will happen if this thing crumbles wholesale…
To Arthur Meyer, thank you for posting the impressive photographs of Chaitén (the town and the volcano)!

9. Bruce - 23 February 2009

I have a couple of questions for the experts here:

1. I fear I have been under the mistaken apprehension that the most gaseous phase of a magma would be erupted first (I guess from the coke bottle analogy). Is it possible that the composition of the magma could change mid-eruption towards greater gas content.. and if so, how likely is that?

2. Someone referred here to a statistic from USGS (I think) or YVO that rhyolite expands 600 fold upon reaching the surface. Obviously that refers to a gas rich melt. What kind of expansion would you expect from the Chaiten magma currently being erupted?

(Or to put it another way, given that roughly <5 cu km has been erupted from Chaiten in total, how much volume does that translate into at the inferred depth of 10 to 12 km that the Chaiten magma is supposedly originating from? )

10. Bruce Stout - 24 February 2009

umm.. let me rephrase that in a way that perhaps doesn’t sound quite so stupid..

assuming Chaitén is getting fed from a sill located at some depth which is being erupted due to top-pressure.. is it a safe assumption to presume that the nature of the magma is unlikely to change radically from that at present? i.e. we can expect more of the same until the sill (presuming it is a sill and not just the tip of a huge diapir!!) is squeezed dry or blocked off.

the second question relates more to the fact that I can’t see how you could get a caldera eruption from such a deep source unless
a) there was a huge volume in the chamber and that volume made it to the surface suddenly (to state the obvious) or
b) the melt contained a lot of dissolved gas that blew out a large cavity upon erupting..

does this make sense?


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