Mount St. Helens eruption caused the worst landslide in world history

On this day in weather history, Mount St. Helens erupted.

This Day In Weather History is a daily podcast by Chris Mei from The Weather Network, featuring stories about people, communities and events and how weather impacted them.


Mount St. Helens is an active stratovolcano (a volcano that is comprised of layers of lava and ash) located in Skamania County, Wash.

On Sunday, May 18, 1980, at 8:32:11 a.m., Mount St. Helens erupted, making it the deadliest and costliest volcanic event in United States history.

MtStHelens Mushroom Cloud

"The ash cloud produced by the eruption, as seen from the village of Toledo, Washington, 35 miles (56 km) away, northwest from Mount St. Helens." Courtesy of Rocky Kolberg/Wikipedia/CC BY-SA 3.0

Two months before the big explosion, there were earthquakes and steam-venting events.

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When it erupted, the entire north face of the mountain slid away. This is the largest landslide recorded in Earth's history. The landslide travelled at 112-240 km/h, with a volume of 2.8 cubic km. The average depth of the landslide was 46 metres but it reached 182 metres deep.

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The volcano sent a mix of lava and pulverized rock toward Spirit Lake. The eruption column reached 24 km high and deposited ash in 11 American states and two Canadian provinces (British Columbia and Alberta).

The eruption caused snow, ice, and even glaciers to melt, creating volcanic mudslides that reached the Columbia River, located almost 80 km away.

During the eruption, the mountain released around 26 megatons of TNT. The eruption killed 57 people directly, including two photographers and a geologist.

Dave Johnston with gas-detection instrument at Mount St. Helens, 4 April 1980 (USGS) 1

"Volcanologist David A. Johnston (photographed on April 4, 1980) was one of the 57 people killed in the eruption." Courtesy of Wikipedia

The volcano also destroyed 200 homes, 47 bridges, railways, highways, and hundreds of square miles of land. The explosion caused $1 billion in damages.

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Throughout the next few days, the volcano let out far less damaging eruptions.

Twenty years after the 1980 eruption, dead trees caused by the blast are still standing.

"Twenty years after the 1980 eruption, dead trees caused by the blast are still standing." Courtesy of Wikipedia

Geologists think that Mount St. Helens will have future eruptions that are even more severe than the 1980 event. Mount St. Helens remains to be a popular hiking spot that is frequented throughout the entire year.

To learn more about the Mount St. Helens eruption, listen to today's episode of "This Day In Weather History."

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Thumbnail: Mount St. Helens. Courtesy of Wikipedia