Although the mainstream media seems to have lost interest in the Chaiten eruption beyond the “human interest” (or should I say “salmon interest”) aspect of the eruption, there is still a lot going on at the volcano. The SERNAGEOMIN recently released this excellent photo of the erupting caldera:
What is pretty clear here is thank a new rhyolite dome is erupting on top of the old dome. (On a side note, when I was visiting the Smithsonian last week, we were all lamenting the fact that no one has come out and said what composition this lava is? I’m 99% convinced it is rhyolite, e.g., high silica, lava, but I haven’t seen an official determination so far EDIT 5/27: Thanks to one of my readers, Hawkeye, for pointing out that the SERNA report I link to above lists the composition as 73-75 wt% silica, a rhyolite). From the looks of the picture, there isn’t a lot of new lava dome on the surface, so much of the volume of erupted material came out in the form of ash and pyroclastic material.
The most recent update from the SERNAGEOMIN show the waning eruption and the new dome:
The eruption is now classified as “sub-plinian”, so a much smaller volume and dispersal area (~5-500 square km). Some of the rivers are choked with volcanic material, mostly ash and pyroclastic material again, but they are creating a lot of lahars.
The seismicity at Chaiten has been gradually going down for the last few days, so this might mean that the eruption is finally winding down – here, a full 3.5 weeks since it started. What is fascinating about this eruption is the idea that what we’re seeing might just be the emplacement of a new dome inside the caldera itself, what is referred to a “resurgent dome”, where eruptions come up through the middle of the caldera after the cataclysmic eruption rather than along the ring fractures at the edge of the caldera. What is yet to be seen is how long is magma was sitting underneath the Chaiten caldera before it erupted and what might triggered such a rapid evacuation of the magma chamber.