Why are the volcanoes mostly located around the Pacific area?
G.
Dvorak
Hi G. Dvorak,
Most of the Earth's volcanoes are located around the Pacific Ocean because
that is where most of the Earth's subduction zones. A subduction zone is
a place where one plate of oceanic lithosphere (= the crust + uppermost
mantle) is shoved under another plate. The downgoing plate eventually
starts to melt, and the material rises up to erupt through the overlying
plate. If the overlying plate is a continent, you get a chain of
volcanoes such as the Andes or Cascades. If the overlying plate is ocean
you get a chain of volcanic islands such as the Marianas or Aleutians.
This is also where the Earth's deep ocean trenches are and where the
Earth's deep earthquakes are. The trenches form because the downgoing
plate is bent downward as it subducts. The earthquakes form as the two
plates scrape against each other (earthquakes down to about 150 km) and
then as the downgoing plate bends (earthquakes down to about 700 km). The
earthquakes do a very good job of tracing the position of the downgoing
plate. These zones of earthquakes are called Wadati-Benioff zones, after
the two seismologists who first recognized them.
These are all a part of plate tectonics-a system that does a very
good job of tying all kinds of geological features together.
I hope this helps to answer your questions.
Sincerely,
Scott Rowland, University of Hawaii
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