The big eruption news today is an unexpected eruption in southern Chile. In fact, it is so unexpected that depending on when and where you read about it, you might get a different answer to what volcano is doing the eruption. What we do know at this point is an eruptive column has been spotted by people on the ground and the Washington VAAC, with estimates of an eruptive column height of between 35-55,000 feet. In other words: pretty darn sizeable. Ash is also coming down in town to the east of the eruption in Argentina. Now it seems that Chilean officials say Volcan Chaiten is the culprit.
The best I can point you towards is the Yahoo! News article which has a nice gallery of images from the eruption.
If you look up Volcan Chaiten in the SI GVP website, the volcano is apparently a caldera system (big volcano with a collapse depression in the center) that last erupted over 7,400 years ago. Mostly it has erupted sticky rhyolite lavas that tend to erupt explosively – which is no great surprised based on early reports of the eruption. If you want a comparison, it sounds like Chaiten might be similar to our own Crater Lake, which last erupted around 7,700 years ago and itself is a caldera.