Can you please tell me how Mt. St. Helens was formed and what type
of rock it is made of? If you could please explain how plate tectonics
and the types of rock that are involved. I would really appreciate it?
Dear Timbo,
Mt. St. Helens is a stratovolcano. It formed by the accumulation of lava
and tephra.
The oldest rocks at Mt. St. Helens are about 40,000-50,000 years old.
Most of the volcano in dacite.
The basics of plate tectonics
are presented in Learning about Volcanoes. Stratovolcanoes tend to be
made of andesite
and are associated with convergent plate boundaries
(subduction zones).
Volcanism is also common at divergent plate boundaries (mid-ocean ridges).
Basalt is the
common rock at this type of boundary.
Steve Mattox, University of North Dakota
Source of Information:
Wood, C.A., and Kienle, J., 1993, Volcanoes of North America: Cambridge
University Press, New York, 354 p.
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