When Nature Strikes - Volcanoes
Volcanoes are both spectacular and dangerous. The most dangerous kind of volcano is the supervolcano. When a supervolcano erupts, it can result in complete local devastation and even a change in global climate. Yellowstone is the site of one supervolcano that erupted most recently 630,000 years ago. Another devastating supervolcano erupted at the Long Valley Caldara in California over 760,000 years ago. Both volcanoes are capable of future eruptions.
Supervolcanoes are so dangerous because of the explosive magma that is produced within the mantle. Shield volcanoes, like the volcanoes of Hawaii, are not explosive because they are composed of basaltic magma produced by a hot spot under the ocean crust. That magma is very liquid and flows easily without an explosion. Under a composite volcano like Mount Saint Helens, the magma produced is intermediate in mineral composition. It is explosive in nature, but not as explosive as the granitic magma that underlies a supervolcano, the most explosive and dangerous kind of volcano in the world.
Michael Manga from the University of California, Berkeley, is investigating the Long Valley supervolcano that erupted hundreds of thousands of years ago, and could do so again.
"When Nature Strikes" is produced by NBC Learn in partnership with the National Science Foundation.
"When Nature Strikes: Volcanoes" Classroom Activity
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