-

Eruption of St. Helens - Gigantic rockslide and debris avalanche

On May 18, 1980, in morning, a magnitude 5.1 earthquake shook Mount St. Helens. The bulge and surrounding area slid away in a gigantic rockslide and debris avalanche, releasing pressure, and triggering a major pumice and ash eruption of the volcano. Thirteen-hundred feet (400 meters) of the peak collapsed or blew outwards. As a result, 24 square miles (62 square kilometers) of valley was filled by a debris avalanche, 250 square miles (650 square kilometers) of recreation, timber, and private lands were damaged by a lateral blast, and an estimated 200 million cubic yards (150 million cubic meters) of material was deposited directly by lahars (volcanic mudflows) into the river channels. Sixty-one people were killed or are still missing. USGS Photograph taken on May 18, 1980, by Austin Post.
St. Helens Eruption
Search For Maps and Images

More Maps and Images