Always late to the party, in this case remembering the 29th anniversary of the eruption of Mt. St. Helens on May 18th, 1980 (here, here, here, and here for other commemorations). I offer another before-and-after picture set (that I also used in one of my first blog entries in the olden days of 18 months ago). [clarification 5/20: before is about 2002, and after is 2006 after the new eruption had begun]
I was graduating from college on the very day the volcano collapsed and exploded. We've referred to our graduating class as the St. Helenians to this day. It was a true tragedy, but geologists have learned so much from the eruption sequence that many thousands of people are alive today because of improved volcano monitoring methods and increased knowledge.
St. Helens has been an excellent outdoor laboratory for my students over the years, and the pictures above show one of the reasons: the volcano is a dynamic geologic environment on a human time scale. The 2004-2008 eruption produced a new dome in the crater of the volcano that is taller than the 1986 dome, and there is no reason to think that the volcano is done yet.