Sometimes I feel like I have nowhere to run to and nowhere to hide that you all cannot find me. Leslie “Bloodhound” Gompf found me first, with Jesper “Volcanomaniac” Sandberg coming in second. Was it my carefully crafted trail of clues that brought you both to Chaitén volcano in Chilé, or was it the 20-kilometer-high column of coffee-scented steam rising from the summit of this highly explosive old mountain that led you to me?
Chaitén is as topographically interesting as it is geologically unique. Had you all decided to virtually hike from the town of Chaitén near the Gulf of Corcovadon in southern Chile, you could just follow the Chaitén river upstream and then take a left-turn and follow a tributary river right up to a breech in the southwest side of the caldera. The mountain itself is sometimes capped by ice and snow, but is not glaciated. Two small lakes reside in the caldera, but apparently briefly disappeared during this volcano’s most recent eruption. But the thing that really makes Chaitén stand out among its volcanic peers is the huge rhyolite lava dome that fills the middle of the caldera. Rhyolite is a highly evolved magma that is felsic (high in silicates, low in iron) that is quite viscous and therefore reticent to release the gas bubbles within it as it rises and decompresses. Thus, the gas finally has to explode its way out of the erupting magma. And as if being highly explosive is not bad enough itself, such thick magma tends to extrude from the volcanic vent like thick clay and form large rounded blobs of new rock around and over the eruptive conduit. These blobs can sometimes collapse while still molten and cause pyroclastic flows, or they can be blasted away from within by subsequent eruptions. The mineral composition of the domes is similar to granite, as is often evident by their appearance. Rhyolite can also take on a glassy appearance, and is called obsidian.
The volcano had always been observed to have a lava dome, and it has been commonly stated (though recently challenged) that Chaitén had not erupted in almost 9,000 years before it came to life again in May of 2008. An increase in seismic activity and early gas emissions from the mountain’s summit at the beginning of May prompted authorities to evacuate the town of Chaitén and other nearby villages. On the 6th of May activity increased to plinian with an eruptive column reaching 10,000 feet (30,000 meters) into the atmosphere. Meanwhile, lahars generated by the eruption destroyed forest and actually clogged and altered the course of the river, causing disastrous flooding in the town of Chaitén Following that initial explosion, the volcano began extruding a new lava dome atop what remained of the old one. Quakes and degassing continued through the year, and in February of 2009 the newly formed lava dome partially collapsed, sending pyroclastic flows that once again threatened the town. The eruption officially ended in May of 2011, but the town of Chaitén has been slow to recover from the damage caused by the flooding and ashfall.
Fortunately for those who live near volcanoes like Chaitén, large rhyolite eruptions are rather rare. In fact until 2008, the only rhyolite eruption in historical times was at Novarupta, in a location so remote that the eruption and its source were initially a mystery…but that’s another volcano for another day.
To see some great images and read more about this volcano, check out this post on PhotoVolcanica’s blog
To read about the volcano from the perspective of the first scientist to climb the summit after the 2008 eruption, check out John Seach’s blog.
Oh..and I almost forgot about the webcam. I must be more alert to those, in case you all should see me sleeping in my volcano-pajamas.
Five points go to Leslie and three to Jesper, and thanks everybody for playing along. Be here this coming Monday….same Volcano-nerd time…same Volcano-nerd place…for a new volcano and a new adventure.