The Long Version: • Western Washington has many earthquakes and volcanoes because we are close to a plate boundary. A small oceanic plate (Juan de Fuca) is sinking under the North American plate. This creates a trench and a Subduction Zone. As the Juan de Fuca plate slides under the North American plate it sometimes catches and great pressure builds up. When the plates snap the pressure is released in the form of an earthquake. The leading edge of the Juan de Fuca plate melts and magma pushes its way to the surface creating volcanoes like Mount Rainier and Mt. St. Helens.
The Short Version: • We live near a plate boundary where two plates are moving. • Sometimes the plates catch as they move and crate stick, pressure building and then slip releasing the energy as an earthquake. • As the ocean plate goes down it melts and creates extra magma that comes back up to make volcanoes.