So far the Chaiten volcano has stuck to the exact script as Mt. Vesuvius for Pompeii and Herculaneum. You have your days of ash, and the column going up 20 miles and scattering the ash over a continent. But what goes up must come down. The volcano runs out of steam, and suddenly all that stuff is concentrated over a much smaller area. The big chimney runs out of pressure and collapses. At that moment all the hot gases and lava just barely pours over the top, and down the sides. As with Pompeii, the looters and the just plain stubborn got engulfed by a giant wall of hot gases.
I find it amazing that we are having the exact same eruption in modern times. Except for the poor people, this is truly a wonder to behold.