22.6 Volcanoes

From northern California through the state of Washington, a chain of snow-capped, cone-shaped mountains rises majestically above the surrounding evergreen forests. These peaks form the backbone of the Cascade Range, which is made up of volcanoes. A volcano is a mountain that forms when magma reaches the surface.

Most of the time, the volcanoes of the Cascade Range are inactive. Occasionally, however, one of these volcanoes erupts with great violence. That's what happened in May 1980, when Mount St. Helens in Washington exploded. This eruption blew away the top of the mountain. It flattened trees as far as 17 kilometers away, and spewed a cloud of ash more than 20 kilometers into the sky, as shown in Figure 38.

Halfway across the Pacific Ocean, on the island of Hawaii, is another volcano called Kilauea. Unlike Mount St. Helens, Kilauea is often active. Lava bubbles out of the ground and quietly flows down gentle slopes. Although Mount St. Helens and Kilauea are both volcanoes, they are quite different from each other. Volcanoes can result from several different geological processes, and can take a variety of forms.

Figure 38 When Mount St. Helens erupted, trapped gases caused the north side of the mountain to explode. Volcanic ash was ejected high into the atmosphere.

Table of Contents