1980 eruption of Mount St. Helens

Mount St. Helens, May 18, 1980

On May 18, 1980 a major volcanic eruption occurred at Mount St. Helens, a volcano located in the state of Washington, United States. The eruption (a VEI 5 event) was the only significant one to occur in the contiguous 48 U.S. states since the 1915 eruption ofLassen Peak in California.[1] 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 huge bulge and a fracture system on the mountain's north slope. An earthquake at 8:32:17 a.m. PDT (UTC−7) on Sunday, May 18, 1980 caused the entire weakened north face to slide away, creating the largest landslide ever recorded. This suddenly exposed the partly molten, gas- and steam-rich rock in the volcano to lower pressure. The rock responded by exploding a hot mix of lava and pulverized older rock toward Spirit Lake so fast that it overtook the avalanching north face.
1980 eruption of Mount St. Helens.
Photograph of the eruption column, May 18, 1980.
Volcano Mount St. Helens 
Date: May 18, 1980 
Type: Plinian, Peléan

An eruption column rose 80,000 feet (24 km; 15 mi) into the atmosphere and deposited ash in 11 U.S. states.[2] 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 in 1980.
1980 eruption of Mount St. Helens
Map of eruption deposits

Fifty-seven people were killed, including innkeeper Harry R. Truman, photographer Reid Blackburn and geologist David A. Johnston.[3] Hundreds of square miles were reduced to wasteland, causing over a billion U.S. dollars in damage ($2.88 billion in 2014 dollars[4]), thousands of game 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 land passed to the United States Forest Service.[5] The area was later preserved, as it was, in the Mount St. Helens National Volcanic Monument.