Another day, another development at Chaiten. Military stationed near the volcano helping with evacuations reported “booming noises” and saw incandescent blocks getting hurled from the vent area. This suggests that lava is at the surface and potentially that the edifice itself is beginning to crack/strain from the loss of material from the eruption. Remember, when you erupt all this volcanic material, you leave a void under the volcano where that magma used to be, so suddenly you have a volcano with no foundation. Sometimes they can founder into that space, forming a caldera. We already know that Chaiten has experienced a caldera-forming eruption before, so it isn’t out of the question.
At the same time, the SERNAGEOMIN says this eruption could go on for days, weeks, maybe months. The big question on everyone’s mind is when the pyroclastic flows will begin, either from eruptions from ring vents in the caldera or from the gravitational collapse of the ash column. Either way, these pyroclastic flows are hot (>>300 C), fast (>100 km/h) and deadly (see also, Mont Pelee). Once the pyroclastic flows start, everything remaining close to the volcano (10s of km) will likely be wiped out.
Looks like we might have a new champion for “largest eruption of the 21st century”!
Edit: Fixed first link (Thanks Bloodfist)