Another story, told by the park rangers at St. Helens:
A couple days after the eruption, geologists helicoptered near the crater and planted a seimograph that sent telemetry back to the USGS Vancouver office. The next day, the USGS was getting some very strange readings from that seimograph, so they assumed it was broken and went out to check it.
When they flew over, they found out what was causing the readings. A small herd of elk had migrated back into the blast zone. The antenna for the seimograph was the tallest thing in the area, and they were rubbing their antlers against it, since there were no trees!
If you get the chance, go visit the Mt. St. Helens National Volcanic Monument. It is absolutely GORGEOUS, and you'll learn a lot!
I was there when it was being built,God I'm old.