Close-Up--Plate Tectonics Theory

Volcanic Arcs

There is typically a lot of andesitic volcanism at suduction zone plate boundaries, and volcanic arcs are formed. If one ocean plate is pushed under another ocean plate, then a volcanic island chain (called an island arc is formed).

Individual Volcanoes in the island are are termed Stratovolcanoes (Composite Volcanoes) because they are very tall and cone shaped.

The andesitic volcanoes, produced by subduction, are explosive and dangerous, creating tsunami as well as pyroclastics, and many people who live on island arcs in Indonesia, Japan, and the Philippines are endangered by this volcanism.

Similarly subduction zones at the edges of continents, where an oceanic plate is pushed under a continental plate, also exhibit much arc-type volcanic activity; for instance, the Andes Mountains of South America and our Cascade Range in California, Washington, and Oregon. The explosion of Mt. St. Helens in Oregon on May 18, 1980, was just a small reminder of the dangers of volcanoes generated by plate tectonics at a subduction zone. For more information visit the US Geological Survey's Volcanic Hazards Web Site.

Click here to visit the USGS Volcanic Hazards Site

USGS Volcanic Hazards Web Site

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