The western United States is home to 20 potentially active volcanoes. Just over half of these have shown activity in the past 2000 years.
The volcanoes of the western United States, especially those in the Cascades, are the result of subduction of oceanic plates beneath the edge of the North American Plate. The oceanic plates are made at mid-ocean ridges and are denser than the North American Plate. The North American Plate is made of continental crust and lithospheric mantle. Water from the oceanic plate helps to melt the hot asthenospheric mantle beneath the North American Plate. Magma rises through the plate to supply volcanoes.
Plate tectonics continues to drive our volcanoes. Eruptions of active volcanoes are imminent but very widespread.
In the bookstore: Volcanoes
On the web: USGS map
Image above: Mount Shasta 1984 (USGS)
Tags: USGS, volcanoes, western us volcanoes
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