What caused the earthquake that triggered the Mt St Helens eruption in 1980?
As in, what sort of plate boundary was it on, ect.
thanks
Chosen Answer:
The fury of the Mount St. Helen blast was attributed to the complex interactions between the Pacific Plate, North American Plate, and tiny Juan de Fuca plate, an area known as a triple plate junction.
On May 18, 1980, a magnitude 5.1 earthquake triggered the collapse of the volcano’s bulging north flank and summit in a landslide of historic proportions. Magma trapped within the volcano, suddenly relieved of pressure, exploded outward in a lateral blast that blew down 230 square miles of forest in less than five minutes. Heat from a rising plume of volcanic ash melted glacial ice creating cement-like slurries of rock and ash called mud flows. Superheated avalanches of hot gas, ash, and pumice called pyroclastic flows flowed into the valley north of the crater. The resulting landscape was a seemingly gray wasteland.
Plates pushing against each other or are colliding produce a convergent plate boundary. This type of boundary results in one plate is being pulled beneath another (subduction) forming a deep trench. The long, narrow zone where the two plates meet is called the subduction zone. Here, a more dense oceanic crust is being subducted under the less dense continental crust. Subduction zones tend to create large, cone-shaped volcanos called stratovolcanos, such as Mt. St. Helens and Mt. Baker in Washington State.
by: Elizabeth H
on: 28th February 09