May 18 - Mount St. Helens

At 8:32 AM Pacific Time on Sunday, May 18, 1980, an earthquake caused the entire north face of Mount St. Helens in Washington state to slide away, instantly exposing volcanic molten magma and gas-enriched rock that had created a huge bulge on the mountain’s side. The resulting landslide was one of the largest in recorded history, completely displacing all of the water in Spirit Lake north of the mountain, washing thousands of trees away from the surrounding hills. The nearly simultaneous volcanic explosion sent out a pyroclastic flow of hot gases, ash and pumice, at near-supersonic speed, into a fan-shaped area 23 miles wide and 19 miles long, destroying 230 square miles of forest. Miles beyond, it killed even more trees with extreme heat. The blast melted nearly all the mountain’s glaciers, resulting in immense lahars (volcanic mudflows). A vast ash column rose 12 miles above the mountain’s expanding crater during the nine-hour eruption. Most of the 57 people known to have died in the event succumbed to asphyxiation; several died from burns.