June 20, 2008

Volcano update...

Alan Sullivan continues to cover Chaitén, which continues to erupt.

...At Chaitén the first stage of dome-building was estimated at 37 cubic meters per second. It has now accelerated past fifty. No wonder the photos are so striking. This is an event outside historic parameters. It is consistent with the large magma chamber implied by the initial earthquakes. But the eruption is rhyolitic. This is a comparatively rare lava with a high silicate content and relatively low sulfur content. Only a few rhyolitic dome formations have been observed. There is virtually no basis for prediction. There is no way to know the significance of recently increased seismic activity and very rapid dome growth. Certainly it seems ominous.

At the least, one must wonder about the mechanical stability of the huge, teetering dome. A simple landslide could release internal pressure and trigger an explosive eruption that would destroy the edifice. It is also possible that rapid evacuation of the magma chamber could lead to a larger collapse of the entire caldera floor. This would probably induce an eruption with serious global consequences. We can only watch and wait.

"Serious global consequences" is no joke. On the other hand there's not much we can do about it! But at least Random Jottings has not failed to keep you informed. The dome is bulking-up at 50 cubic meters per second. That's hard to imagine. An old pick-up truck I used to own would hold about one cubic meter of soil.

Alan links to some awesome pictures....

....The Volcanism Blog has published an awesome aerial photo sequence from June 17, when the weather was clear. The eruption was increasing in intensity. The photos show steam emission at locations near the dome base, thick fume rising off the dome itself, and intense ash pluming from the new crater. The old crater may have been choked off by growth of the dome, which would explain pressure buildup sufficient to blast a new crater. But the base fumaroles, though small in comparison, may be more significant. They could imply the fracturing preliminary to dome collapse, as the partially emptied magma chamber undermines the massive and growing lava pile. Such a collapse would trigger explosive release of all the remaining pressure in the magma chamber, and perhaps also the deeper conduit that feeds it. Recall that we had reason from the pattern of the initial earthquake sequence to suspect that magma chamber was very large.

I’m not a geologist, and these are no more than half-educated speculations. It seems to me there is ample reason for concern, even some degree of alarm. We are not speaking of a model based on dubious data. We are witnessing a natural process which, in the geological record, has often led to world-class eruptions. This phenomenon coincides with — and could significantly amplify a period of global cooling...
Posted by John Weidner at June 20, 2008 7:03 PM
Weblog by John Weidner