Background of Mount St. Helens Mount St. Helens is a volcano located in Washington State in the United States of America. It has been around for over 275,000 years, and it is the most active volcano in the Cascade Range. Mount St. Helens remained a relatively quiet volcano until about 3000 years ago. As Mount St. Helens has grown to its height of 9,677 feet, large amounts of basalt and andesite began to erupt as lava flows, along with flows of dacite. An interesting fact about Mount St. Helens is that volcanism occurs at Mount St. Helens and along the Cascade Range due to subduction of the Juan de Fuca plate off the western coast of North America.
Causes of the Mount St. Helen's Eruption of 1980 Before Mount St. Helens started erupting, there were multiple small earthquakes that exploded in the spring. Along with the earthquakes, there were steam explosions (also in the spring of 1980). Scientists also looked into the eruption in order to figure out why the volcano erupted in the first place. They discovered that there was an interaction between silicic (dacite) magma with more mafic (basalt to andesite) magma that increased the volcanism in Mount St. Helen, therefore causing an eruption. Another cause of the eruption is that Mount St. Helens lies near a boundary plate that destructive plate boundary (Juan de Fuca) that is being forced into the mantle by the bigger North American plate. Since the boundary plate is being forced into the mantle, friction and heat is occurring. That friction and heat caused the plate to melt and turn into molten rocks. After all of the disturbances, the volcano finally erupted March 27, 1980, after 100 years of not erupting.