Mount St. Helens, Washington

Mount St. Helens, Washington, erupted 40 years ago, on May 18, 1980. A massive debris avalanche, triggered by an earthquake of magnitude 5.1, caused a lateral eruption that reduced the elevation of the mountain's summit from 2,950 m to 2,549 m, leaving a 1.6 km wide horseshoe-shaped crater. The collapse of the northern flank resulted in massive volcanic mudflows. Since 1980, new lava built a dome in the crater, and occasional steam and ash plumes have been emitted.