Today marks the 30th anniversary of the eruption of Washington State's Mt. St. Helens. Seismologists, scientists who study earthquakes, recorded significant activity in the months prior to the eruption.
The lateral blast was recorded at a velocity of over 300 mph, and damaged enough trees to build 300,000 two-bedroom homes. The ash cloud resulting from the eruption spread across the U.S. in only three days, and spanned the globe in 15. For more facts, visit http://vulcan.wr.usgs.gov.