Volcanoes

October 21, 1983

Report Outline
Recent Volcanic Eruptions
Causes and Consequences
Possible Impact on Weather

Recent Volcanic Eruptions

Fallout from Mount St. Helens, El Chichón

It may be the most impressive sight in nature. Few people can look at an erupting volcano — even on television or in a still photograph — without getting a sense of nature's raw power. This sight has not been all that unusual in recent years. In the first week of October, for example, there were two significant volcanic eruptions. On Oct. 3, Japan's Mount Oyama on the island of Miyake erupted for the first time in 21 years, burying a village and sending black smoke over six miles into the air. Two days later, the Kilauea volcano on the island of Hawaii erupted for the tenth time since early January.

There was no loss of life in either of these incidents. This was not the case, however, with two catastrophic volcanic eruptions that occurred in the opening years of this decade. Early on the morning of May 18, 1980, Mount St. Helens in Washington state blasted 1,300 feet from its top with the destructive force of 26 megatons of TNT. The enormous force of the eruption knocked down timber over a 232-square-mile expanse. Sixty people died, most instantly. Three times as many people perished in the April 1982 eruptions of El Chichón in southeastern Mexico. Thousands of Zoque Indians, who eked out a living by farming the volcano's fertile slopes, were forced to flee their homes.

Both mountains have simmered down, but they continue to be objects of intense scientific study. The U.S. Geological Survey established the Cascades Volcano Observatory in Vancouver, Wash., in late 1980 to closely monitor Mount St. Helens and 15 other Cascade Range volcanoes. A recent report published by the agency concluded that the historic record of past eruptions of Cascade volcanoes, “together with current evidence of increased seismic and other precursory activity in the Western United States, strongly suggests that the threat of volcanic eruptions in the near future has not diminished.” Eruptions at Mount St. Helens are expected to continue intermittently for the next 20 to 30 years.

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