Eruption Style!

Mt. St. Helens is an explosive stratovolcano that has a lava dome that has an area of about 97 million cubic yards. This lava dome contains rhyolitic magma which is roughly 650 to 800 degrees Clecius. Rhyolitic magma has a high viscosity and is 1 to 100 million times more viscous than water. When Mt. St. Helen's erupts, there is a good chance that there will be pyroclastic flows, debris avalanches, flooding, and lahars (mud flows). Prior to an eruption, you can usually expect earthquakes. When Mt. St. Helens erupted on May 18, 1980 it had a lateral blast of 300 miles per hour that swept out of the north side.