What happened during the 1980 eruption of Mount St. Helens?

The 1980 eruption of Mount Saint Helens, located in the Cascade Range, was one of the most significant volcanic events in North America.1

On the morning of May 18, 1980, a 5.1-magnitude earthquake triggered a massive landslide on the mountain's north face. This collapse was followed by a high-velocity lateral air blast of superheated ash and stone that traveled at speeds of at least 300 miles per hour, devastating an area of approximately 200 square miles. Simultaneously, a vertical column of gas and ash rose 16 miles into the atmosphere, causing widespread ash fall.12

The event resulted in the deaths of 57 people and thousands of animals. The eruption completely destroyed the volcano's original 9,677-foot peak, leaving behind a horseshoe-shaped crater. Subsequent mudflows, pyroclastic flows, and floods buried surrounding river valleys in deep debris.12