Natural Disasters Disasters
On March 27, 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. It initiated as a series of phreatic blasts from the summit then escalated on May 18, 1980, as a major explosive eruption. The eruption, which had a Volcanic Explosivity Index of 5, was the most significant to occur in the contiguous 48 U.S. states since the much smaller 1915 eruption of Lassen Peak in California. It has often been declared the most disastrous volcanic eruption in U.S. history.
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 a.m. PDT (UTC−7) on Sunday, May 18, 1980, caused the entire weakened north face to slide away, creating the largest landslide recorded. This allowed the partly molten, high-pressure gas- and steam-rich rock in the volcano to suddenly explode northwards toward Spirit Lake in a hot mix of lava and pulverized older rock, overtaking the avalanching face.
An eruption column rose 80,000 feet (24 km; 15 mi) into the atmosphere and deposited ash in 11 U.S. states and significant ash in two Canadian provinces. 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. Thermal energy released during the eruption was equal to 26 megatons of TNT.
Approximately 57 people were killed directly, including innkeeper Harry R. Truman, photographers Reid Blackburn and Robert Landsburg, and geologist David A. Johnston. Hundreds of square miles were reduced to wasteland, causing over $1 billion in damage (equivalent to $3.4 billion in 2019), 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 land passed to the United States Forest Service. The area was later preserved, as it was, in the Mount St. Helens National Volcanic Monument.
On March 20, at 3:45 p.m. Pacific Standard Time (all times will be in PST or PDT), a shallow magnitude 4.2 earthquake centered below the volcano's north flank, signaled the volcano's return from 123 years of hibernation. A gradually building earthquake swarm saturated area seismographs and started to climax at about noon on March 25, reaching peak levels in the next two days, including an earthquake registering 5.1 on the Richter scale. A total of 174 shocks of magnitude 2.6 or greater were recorded during those two days. More details
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 a.m. PDT (UTC−7) on Sunday, May 18, 1980, caused the entire weakened north face to slide away, creating the largest landslide recorded. This allowed the partly molten, high-pressure gas- and steam-rich rock in the volcano to suddenly explode northwards toward Spirit Lake in a hot mix of lava and pulverized older rock, overtaking the avalanching face.
An eruption column rose 80,000 feet (24 km; 15 mi) into the atmosphere and deposited ash in 11 U.S. states and significant ash in two Canadian provinces. 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. Thermal energy released during the eruption was equal to 26 megatons of TNT.
Approximately 57 people were killed directly, including innkeeper Harry R. Truman, photographers Reid Blackburn and Robert Landsburg, and geologist David A. Johnston. Hundreds of square miles were reduced to wasteland, causing over $1 billion in damage (equivalent to $3.4 billion in 2019), 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 land passed to the United States Forest Service. The area was later preserved, as it was, in the Mount St. Helens National Volcanic Monument.
Mount St. Helens remained dormant from its last period of activity in the 1840s and 1850s until March 1980. Several small earthquakes, beginning on March 15, indicated that magma might have begun moving below the volcano.
