Debris avalanche deposit from the May 18, 1980 eruption of Mount St...

The volume of the debris avalanche was nearly 2/3 cubic miles (2.5 cubic kilometers) of debris avalanche that slid from the volcano on May 18, 1980. That is enough material to cover Washington, D.C. to a depth of 14 feet (4 meters). The avalanche traveled approximately 15 miles (24 kilometers) downstream at a velocity exceeding 150 miles per hour (240 km/hr). It left behind a hummocky deposit with an average thickness of 150 feet (45 meters) and a maximum thickness of 600 feet (180 meters).