1980 eruption of Mount St. Helens
On March 27, 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of phreatic blasts occurred from the summit and escalated until a major explosive eruption took place on May 18, 1980, at 8:32 am. The eruption, which had a volcanic explosivity index of 5, was the first to occur in the contiguous United States since the much smaller 1915 eruption of Lassen Peak in California.[2] It has often been declared the most disastrous volcanic eruption in U.S. history.
"Eruption of Mount St. Helens" redirects here. For other eruptions, see Mount St. Helens § Geology.1980 eruption of Mt. St. Helens
(climactic episode) May 18, 1980[1]
5[1]
Approximately 57 deaths, about $1.1 billion in property damage ($3.4 billion in 2023); caused a collapse of the volcano's northern flank, deposited ash in eleven U.S. states and five Canadian provinces
The eruption was preceded by a two-month series of earthquakes and steam-venting episodes caused by an injection of magma at shallow depth below the volcano that created a large bulge and a fracture system on the mountain's north slope. An earthquake at 8:32:11 am PDT (UTC−7) on May 18, 1980,[3] caused the entire weakened north face to slide away, a sector collapse which was the largest subaerial landslide in recorded history.[4] This allowed the partly molten rock, rich in high-pressure gas and steam, to suddenly explode northward toward Spirit Lake in a hot mix of lava and pulverized older rock, overtaking the landslide. An eruption column rose 80,000 feet (24 km; 15 mi) into the atmosphere and deposited ash in 11 U.S. states[5] and various Canadian provinces.[6] At the same time, snow, ice, and several entire glaciers on the volcano melted, forming a series of large lahars (volcanic mudslides) that reached as far as the Columbia River, nearly 50 miles (80 km) to the southwest. Less severe outbursts continued into the next day, only to be followed by other large, but not as destructive, eruptions later that year. The thermal energy released during the eruption was equal to 26 megatons of TNT.[7]
About 57 people were killed, including innkeeper and World War I veteran Harry R. Truman, photographers Reid Blackburn and Robert Landsburg, and volcanologist David A. Johnston.[8] Hundreds of square miles were reduced to wasteland, causing over $1 billion in damage (equivalent to $3.4 billion in 2023), thousands of animals were killed, and Mount St. Helens was left with a crater on its north side. At the time of the eruption, the summit of the volcano was owned by the Burlington Northern Railroad, but afterward, the railroad donated the land to the United States Forest Service.[9][10] The area was later preserved in the Mount St. Helens National Volcanic Monument and due to the eruption, the state recognized the month of May as "Volcano Awareness Month" and events are held at Mt. St. Helens, or within the region, to discuss the eruption, safety concerns, and to commemorate lives lost during the natural disaster.[11]
Satellite image of Mount St. Helens crater (22 July 1982)
Satellite image of Mount St. Helens crater 30 June 1980 (color infrared)
Satellite image of Mount St. Helens before eruption (23 July 1975)
