Mount Saint Helens erupted explosively on May 18, 1980, at 8:32 a.m. Pacific Daylight Time. The eruption was triggered by a magnitude 5.1 earthquake that caused the north face of the mountain to collapse, resulting in the largest debris avalanche in recorded history. This was followed by a powerful lateral blast, pyroclastic flows, mudflows, and a vertical ash column that reached about 16 miles high. The eruption caused massive destruction, lowering the mountain's elevation by about 1,314 feet, and had widespread ashfall across several states. The eruption was preceded by a series of earthquakes and smaller eruptions starting in March 1980, with the first steam explosion occurring on March 27, 1980.
