The Pacific plate is moving north toward Alaska at a rate of over 2 inches per year and is being thrust beneath the Aleutians and southern Alaska. This boundary between the North American and Pacific plates is convergent. Volcanoes form as a result of melting associated with the subducting plate.

Image courtesy of Alaska Earthquake Center

Several of Earth's largest earthquakes have occurred along this interface. The largest rupture of the Aleutian Megathrust was the magnitude 9.2 Great Alaska Earthquake in March 1964.