How old is Mount St. Helens?

The eruptive history of Mount St. Helens began about 40,000 years ago with dacitic volcanism, which continued intermittently until about 2,500 years ago. This activity included numerous explosive eruptions over periods of hundreds to thousands of years, which were separated by apparent dormant intervals ranging in length from a few hundred to about 15,000 years.

The range of rock types erupted by the volcano changed about 2,500 years ago. Since then, Mount St. Helens repeatedly has produced lava flows of andesite, and produced basalt on at least two occasions. Other eruptions during the last 2,500 years produced: dacite and andesite pyroclastic flows and lahars as well as dacite, andesite, and basalt airfall tephra. Major intervals of dormancy over the last 2,500 years range in length from about 200 to 700 years.

Learn more: USGS Cascades Volcano Observatory

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Image shows a map with potential volcano hazards to the surrounding area for Mount St. Helens
November 30, 2000

Mount St. Helens Simplified Volcano Hazards Map

Mount St. Helens, Washington simplified hazards map showing potential impact area for ground-based hazards during a volcanic event. More simplified volcano hazard maps for the other Cascades Volcanoes can be found here.

Image shows two scientists on the slopes of Mount St. Helens with steam rising around them
September 24, 1981

Gas Sampling around the Mount St. Helens Dome

USGS geologists gathered samples by hand from vents on the dome and crater floor. Additionally, sulfur dioxide gas was measured from a specially equipped airplane before, during, and after eruptions to determine "emission rates" for the volcano.

Mount St. Helens soon after the May 18, 1980 eruption
September 10, 1980

Mount St. Helens soon after the May 18, 1980 eruption

Mount St. Helens soon after the May 18, 1980 eruption, as viewed from Johnston's Ridge.

Volcano erupting and spewing a huge cloud of rock and ash into the sky.
May 18, 1980

Mount Saint Helens eruption

On Sunday, May 18, 1980 at 8:32 a.m., the bulging north flank of Mount St. Helens slid away in a massive landslide -- the largest in recorded history. Seconds later, the uncorked volcano exploded and blasted rocks northward across forest ridges and valleys, destroying everything in its path within minutes.

Aerial photo of Mount St. Helens volcano, pre-1980 eruption
September 28, 1979

Aerial photo of Mount St. Helens volcano, pre-1980 eruption

Before the eruption of May 18, 1980, Mount St. Helens' elevation was 2,950 m (9,677 ft). View from the west, Mount Adams in distance. S. Fork Toutle River is valley in center of photo.

Mount Adams elevation is 3,745 m (12, 286 ft). Mount St. Helens was the smallest of five major volcanic peaks in Washington State.

Mount St. Helens

Mount St. Helens

Prior to 1980, Mount St. Helens had the shape of a conical, youthful volcano sometimes referred to as the Mount Fuji of America. During the 1980 eruption the upper 400 m (1,300 ft) of the summit was removed by a huge 

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