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, and since then, Mount St. Helens repeatedly has produced lava flows of andesite, and on at least two occasions - basalt. 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 dormant intervals of the last 2,500 years range in length from about 200 to 700 years.

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Which volcanic eruptions were the deadliest?

Deadliest Volcanic Eruptions Since 1500 A.D. Eruption Year Casualties Major Cause Nevado del Ruiz, Colombia 1985 25,000 1,3 Mudflows 3 Mont Pelée, Martinique 1902 30,000 1 (29,025) 2 Pyroclastic flows 2 Krakatau, Indonesia 1883 36,000 1 (36,417) 2 Tsunami 2 Tambora, Indonesia 1815 92,000 1,2 Starvation 2 Unzendake, Japan 1792 15,000 1 (14,030) 2...

How would an eruption of Mount Rainier compare to the 1980 eruption of Mount St. Helens?

Eruptions of Mount Rainier usually produce much less volcanic ash than do eruptions at Mount St. Helens. However, owing to the volcano's great height and widespread cover of snow and glacier ice, eruption-triggered debris flows ( lahars ) at Mount Rainier are likely to be much larger -- and will travel a greater distance -- than those at Mount St...

How much ash was there from the May 18, 1980 eruption of Mount St. Helens?

During the 9 hours of vigorous eruptive activity on May 18, 1980, about 540 million tons of ash from Mount St. Helens fell over an area of more than 22,000 square miles. The total volume of the ash before its compaction by rainfall was about 0.3 cubic mile, equivalent to an area the size of a football field piled about 150 miles high with fluffy...

What is the origin of the name "Mount St. Helens"?

Some Indians of the Pacific Northwest variously called Mount St. Helens 'Louwala-Clough,' or 'smoking mountain.' The modern name, Mount St. Helens, was given to the volcanic peak in 1792 by seafarer and explorer Captain George Vancouver of the British Royal Navy. He named it in honor of fellow countryman Alleyne Fitzherbert, who held the title ‘...

How many eruptions have there been in the Cascades during the last 4,000 years?

Eruptions in the Cascades have occurred at an average rate of one to two per century during the last 4,000 years. Future eruptions are certain. Learn more: Eruptions in the Cascade Range During the Past 4,000 Years USGS Cascades Volcano Observatory

How far did the ash from Mount St. Helens travel?

The May 18, 1980 eruptive column at Mount St. Helens fluctuated in height through the day, but the eruption subsided by late afternoon. By early May 19th, the eruption had stopped. By that time the ash cloud had spread to the central United States. Two days later, even though the ash cloud had become more diffuse, fine ash was detected by systems...

How high was Mount St. Helens before the May 18, 1980 eruption? How high was it after?

Before May 18, 1980, Mount St. Helens ' summit altitude of 9,677 feet (2,950 meters) made it only the fifth highest peak in Washington State. It stood out handsomely, however, from surrounding hills because it rose thousands of feet above them and had a perennial cover of ice and snow. The peak rose more than 5,000 feet (1,524 meters) above its...

What was the largest volcanic eruption in the 20th century?

The World's largest eruption of the 20th century occurred in 1912 at Novarupta on the Alaska Peninsula. An estimated 15 cubic kilometers of magma was explosively erupted during 60 hours beginning on June 6th. This volume is equivalent to 230 years of eruption at Kilauea (Hawaii) or about 30 times the volume erupted by Mount St. Helens (Washington...

Will extinct volcanoes on the East Coast of the U.S. erupt again?

No. Through plate tectonics, the eastern U.S. has been isolated from the global tectonic features (tectonic plate boundaries and hot spots in the mantle), that cause volcanic activity. So new volcanic activity is not possible now or in the near future. If you wait around several hundred million years, maybe... Remnants of past volcanism are found...

Which volcanoes in the conterminous United States have erupted since the Nation was founded?

Excluding steam eruptions, these volcanoes have shown activity: Mount St. Helens, Washington - Eruptions and/or lava dome growth occurred in the late 1700s, 1800-1857, 1980-1986, and 2004-2007. Lassen Peak, California - A series of steam blasts began on May 30, 1914. An eruption occurred 12 months later on May 21, 1915. Minor activity continued...

Where does the United States rank in the number of volcanoes?

The United States ranks third, behind Indonesia and Japan, in the number of historically active volcanoes (that is, those for which we have written accounts of eruptions). In addition, about 10 percent of the more than 1,500 volcanoes that have erupted in the past 10,000 years are located in the United States. Most of these volcanoes are found in...

What was the most destructive volcanic eruption in the history of the United States?

The May 18, 1980 eruption of Mount St. Helens (Washington) was the most destructive in the history of the United States. Novarupta (Katmai) Volcano in Alaska erupted considerably more material in 1912, but owing to the isolation and sparse population of the region, there were no human deaths and little property damage. In contrast, the eruption of...
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Date published: May 18, 2017

Ever Vigilant: USGS Marks the 37th Anniversary of Mount St. Helen's Eruption and the 35th Anniversary of the Cascades Volcano Observatory

Today, in 1980, Mount St. Helens unleashed the most devastating eruption in U.S. history. Two years later, USGS founded the Cascades Volcano Observatory to monitor Mount St. Helens and all the Cascades Volcanoes.

Date published: May 17, 2017

EarthWord–Phreatic Eruption

This EarthWord is straight up steampunk...

Date published: May 16, 2017


Which sounds more dangerous, lava or mud? The answer may surprise you...

Date published: May 1, 2017

May is Volcano Preparedness Month in Washington State

May is Volcano Preparedness Month in Washington, providing residents an opportunity to become more familiar with volcano hazards in their communities and learn about steps they can take to reduce potential impacts.

Date published: September 12, 2016


It’s not flirting for submarines, but this week’s EarthWord does feature the ocean...

Date published: August 22, 2016


Look! In the sky! It’s a bird, it’s a plane! Wait, run, it’s this week’s EarthWord!

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Mount St. Helens before and after 1980 eruption
May 9, 2016

Mount St. Helens before and after 1980 eruption

Left: 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.

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

Image shows a scientific instrument on the slopes of Mount St Helens
August 6, 2013

Precise Surveying of Mount St. Helens Crater with RTK-GPS Technology

A survey base station is established using a RTK-GPS receiver with mobile units to collect data points in and around the crater. Information will be used to monitor surface changes, deformation, erosion and aggradation inside the crater. This type of technology is precise to the centimeter. View is to the south of Mount St. Helens, toward Crater Glacier and the lava domes

video thumbnail: Volcano Hazards
July 30, 2012

Volcano Hazards

The United States has 169 active volcanoes. More than half of them could erupt explosively, sending ash up to 20,000 or 30,000 feet where commercial air traffic flies. USGS scientists are working to improve our understanding of volcano hazards to help protect communities and reduce the risks.

Video Sections:

  • Volcanoes: Monitoring Volcanoes
video thumbnail: Mount St. Helens: May 18, 1980
May 10, 2010

Mount St. Helens: May 18, 1980

USGS scientists recount their experiences before, during and after the May 18, 1980 eruption of Mount St. Helens. Loss of their colleague David A. Johnston and 56 others in the eruption cast a pall over one of the most dramatic geologic moments in American history.

video thumbnail: Mount St. Helens: A Catalyst for Change
May 10, 2010

Mount St. Helens: A Catalyst for Change

The May 18, 1980 eruption of Mount St. Helens triggered a growth in volcano science and volcano monitoring. Five USGS volcano observatories have been established since the eruption. With new technologies and improved awareness of volcanic hazards USGS scientists are helping save lives and property across the planet.

December 31, 2006

Mount St. Helens 2004-2008 Eruption: A Volcano Reawakens

Mount St. Helens reawakened in late September 2004. Small magnitude earthquakes beneath the 1980-1986 lava dome increased in frequency and size, and a growing welt formed on the southeast margin of the previous lava dome and nearby portions of Crater Glacier. On October 1, 2004, the first of several explosions shot a plume of volcanic ash and gases from a vent on the

December 31, 2004

Mount St. Helens eruption highlights: September 2004 - May 2005

Compilation video of significant events from the dome-building eruption at Mount St. Helens, from October 1, 2004 to March 15, 2005, including steam and ash eruptions, growth of lava spines, helicopter deployment of monitoring equipment, collection of lava samples, and FLIR thermal imaging of rock collapse on lava dome.

  1. Eruption of Mount St. Helens,  October 1
Image shows damage from a lahar, including a submerged bridge
November 30, 2000

Mount St Helens Lahar

Bridge destroyed by lahar in North Fork Toutle River during eruption of Mount St. Helens, May 18,1980. Credit: Richard Waitt, USGS.

Image shows billowing clouds of steam and smoke emanating from the ground
November 30, 2000

Mount St Helens Phreatic Eruption

Phreatic eruption at the summit of Mount St. Helens, Washington. Credit: D.A. Swanson, USGS