Probably the best known volcanic eruption by Americans, Mt. St. Helens erupted May 18th, 1980.  The picture on the left was taken during the eruption, and the picture on the right is current.  While there was little loss in human life, it devasted hundreds of square miles of old-growth forest, probably killing thousands of spotted owls at the same time.  In the current picture, note that the crater is open on one side, and much of the top of the mountain seems to be missing.  This is because the upper third of the mountain disappeared in the first minutes of the eruption in a massive land slide.