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Introduction
There are many different kinds of volcanoes, ranging from the Hawaiian type,
which produces gentle, effusive eruptions that tourists can observe from mere
steps away, to the andesitic variety, which can produce violent, life-threatening
Plinian eruptions with little or no warning. Though volcanologists study all
types of volcanoes, the latter kind is of greatest concern since it is capable
of killing thousands of people, destroying entire cities and forests, and
severely disrupting local economies.
The volcanoes featured in the NOVA program "Volcano's Deadly Warning"—Galeras, Nevado del Ruiz, Popocatepetl, and Mt. Redoubt—as well as many other
famous volcanoes, including Mt. St. Helens and Mt. Vesuvius, are all andesitic
volcanoes. Here, get to know the major features and products of an
andesitic volcano, which forms when two tectonic plates rub against each other
and generate enough friction and heat to create magma from melted rock. This
magma surges through the surface of the earth, then solidifies, resulting over
time in a classic volcano cone. —Lexi Krock
Note: Some of the text in this feature is adapted from materials produced by the U.S.
Geological Survey. An extensive volcano glossary can be found at
volcanoes.usgs.gov.
Above left: Mt. St. Helens, a grande dame among andesitic volcanoes,
erupts on July 22, 1980.
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