This image shows the difference in elevation of Mt. St. Helens after it erupted. The darkest blue represents a difference of -3,384 feet, and the darkest red represents a difference of 395 feet. My assumption is that the increase in elevation occurred because of lava flows in most areas around the mountain, but the largest increase in elevation (to the north) shows where the top of the mountain ended up. These data sets are great, and a nice resource from the USGS.