Is there a subduction zone that caused Mount St. Helens to become
active and if so what is going on there now?
Audrey
Dear Audrey,
Yes, there is a subduction zone associated with Mount St. Helens and the
other Cascade volcanoes. The subduction zone has been there a long time,
20 million years or so. It results from the
subduction
of the Juan de Fuca oceanic plate beneath the North American
plate. At the present time, the Juan de Fuca plate is moving to the
east-southeast at about 3 cm/year and the North American plate is moving
to the southwest at 2.3 cm/yr. Because the oceanic plate is denser it is
pushed beneath the continental part of the North American plate, which is
made of rocks with lower densities.
The 1980 eruption at Mount St. Helens is only the most recent at that
volcano. The oldest deposits at Mount St. Helens are 40,000 to 50,000
years old.
Steve Mattox, University of North Dakota
Sources of Information:
Wood, C.A., and Kienle, J., 1990, Volcanoes of North America: Cambridge
University Press, New York, 354 p.
The Dynamic Planet by Simkin, T.,
and others.
Other Categories
Other Questions
To VolcanoWorld