Anniversary of the Mount St. Helens eruption

Today in science: On May 18, 1980, Mount St. Helens underwent a catastrophic and deadly eruption, triggering the largest landslide ever recorded. Earlier in the year, thousands of small earthquakes, venting steam, and a growing bulge protruding 450 feet (140 m) indicated that magma was rising in the volcano. Then, at 8:32 a.m. local time 41 years ago today, a 5.1-magnitude earthquake rocked the mountain, triggering the huge landslide and lateral blast that collapsed the volcano’s northern face. Hot pressurized magma erupted, and the ash plume reached a towering height of 80,000 feet (15 miles, 24 km), before blanketing the surrounding region. A Unites States Geological Survey (USGS) geologist described the destructive blast:

It completely destroyed an area of 230 square miles in a matter of five to nine minutes. It essentially killed everything within that area.

Fifty-seven people, including volcanologist David A. Johnston and photojournalist Reid Blackburn, were killed during the May 18, 1980, eruption at Mount St. Helens. The Johnston Ridge Observatory in Toutle, Washington, was named for the late volcanologist. As of May 10, 2021, while the Observatory itself is closed with no firm opening date, the plaza area behind the building with an incredible view of the crater and volcano, and blast zone, is open.

Snowcapped mountain with water in foreground.
Before: Mount St. Helens photographed seven years prior to the 1980 eruption. Image via U.S. Forest Service/
Snowcapped mountain with crater at summit, smoke plume from the center, clouds behind and a reflection in the foreground water.
After: Mount St. Helens photographed two years after the 1980 eruption. Image via Lyn Topinka/ USGS.

The dense forest that covered the slopes of the volcano was reduced to ash inside an area known as the inner blast zone, which extended about 6.2 miles (10 km) from the summit. Trees farther away from the inner blast zone were also damaged by the searing heat. The total extent of the devastated forested area is known as the blowdown zone. Over the past decades, this area has slowly rebounded with life.

Mountainous area covered in fallen logs.
This aerial view of timber blowdown was taken on June 8, 1980, after it was leveled by the Mount St. Helens eruption. Image via USGS/
Satellite image view of volcano Mount St. Helens.
Mount St. Helens on April 20, 2015. Read more about this image at NASA Earth Observatory. Image via NASA Earth Observatory.

Lahars – mudflows carrying debris from volcanic eruptions – formed rapidly from the melting ice and snow on Mount St. Helens’s flanks. The massive lahars created in the 1980 eruption damaged homes, roads and bridges in nearby communities.

Logs beside large toppled trucks.
Massive lahars swept timber, trucks and any debris in its path with it down the mountainside at Mount St. Helens on May 18, 1980. Image via D. Olson/ National Park Service.

Mount St. Helens stands today as an 8,363-foot (2,550-m) high stratovolcano located in Skamania County, Washington, some 1,300 feet (400 m) shorter than before its 1980 eruption. It is the most active volcano in the Cascade Range, which runs along the northwestern coast of North America. The Cascade Range is part of the Pacific Ring of Fire. Mount St. Helens is still considered one of the most dangerous volcanoes in the United States.

Since 1980, Mount St. Helens has continued to experience periodic earthquakes and volcanic eruptions, but not to the same extent of that seen in 1980. The Cascades Volcano Observatory continually monitors activity at Mount St. Helens.

Gray and black cauliflower-like clouds over volcano.
Photograph of Mount St. Helens taken during the May 18, 1980, eruption. Image via Oman/ Combs/ National Park Service.

Bottom line: Mount St. Helens volcano exploded in a cataclysmic event on May 18, 1980, killing 57 people and dramatically altering the landscape.

View more Mount St. Helens eruption videos

Magma rising inside Mount St. Helens, but no eruption expected

View from space: Life reclaims Mount St. Helens

What is the Ring of Fire?

May 18, 2021

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Deanna Conners

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