What is the greatest hazard presented by Mount Rainier?

Debris flows (lahars) pose the greatest hazard to people near Mount Rainier. A debris flow is a mixture of mud and rock debris that looks and behaves like flowing concrete. Giant debris flows sometimes develop when large masses of weak, water-saturated rock slide from the volcano's flanks. Many of these debris flows cannot be predicted and may even occur independently of a volcanic eruption.

Giant debris flows can also form during an eruption as hot rock fragments tumble down the volcano's slopes, eroding and melting snow and glacier ice. Although they happen infrequently, giant debris flows have the potential to inundate much of the southern Puget Sound lowland. Scientists estimate that debris flows can travel the distance between Mount Rainier and the Puget Sound lowland in as little as 30 minutes to a few hours. About 100,000 people now live in areas that have been buried by debris flows during the past few thousand years.

During the past 10,000 years, about 60 giant debris flows from Mount Rainier have filled river valleys to a depth of hundreds of feet near the volcano, and have buried the land surface under many feet of mud and rock sixty miles downstream. Seven debris flows large enough to reach Puget Sound have occurred in the past 6,000 years. 

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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 dangerous is Mount Rainier?

Although Mount Rainier has not produced a significant eruption in the past 500 years, it is potentially the most dangerous volcano in the Cascade Range because of its great height, frequent earthquakes , active hydrothermal system , and extensive glacier mantle. Mount Rainier has 26 glaciers containing more than five times as much snow and ice as...

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 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...

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...
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PubTalk 2/2018 — USGS Cascades Volcano Observatory

Title: The USGS Cascades Volcano Observatory - Research, monitoring, and the science of preparing society for low-probability, high-consequence events

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Damage from Nevado del Ruiz Lahar

In November 1985, a lahar (volcanic mudflow) originating from Nevado del Ruiz volcano inundated the town of Armero, destroying all infrastructure in its path and killing 23,000 people. VDAP was developed in response to this tragedy. Photograph credit: USGS/VDAP

 Mt. Rainier Lahar Hazard Map
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Volcano hazard map showing the extent of lahar hazards in towns and valleys surrounding Mt. Rainier in Washington. Image credit: USGS

Photograph of Mount Rainier and Orting, Washington
April 11, 2016

Photograph of Mount Rainier and Orting, Washington

Photograph of Mount Rainier and Orting, Washington, as seen from a ridge to the west. Orting is one of many communities that are in lahar-prone areas below the flanks of Mount Rainier. 

Large snow-covered, cone shaped mountain in background, looming over urban area in foreground
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Mount Rainier looms over the Puyallup Valley, Washington

Mount Rainier volcano looms over Puyallup Valley, near Orting, Washington.

Large snow-covered, cone shaped mountain in background, looming over suburban area in foreground
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Mount Rainier Looms over the Puyallup Valley, Washington

Mount Rainier volcano looms over Puyallup Valley, near Orting, Washington.

video thumbnail: Mount St. Helens: A Catalyst for Change
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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.

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February 8, 2010

Debris Flow Damage

House engulfed by debris flows generated in response to a rainstorm on February 6, 2010. This house was west of Briar Wood Canyon in southern California. The small, but steep and rugged drainage basin above this home was burned the previous summer by the Station Fire, the largest fire in the history of Los Angeles County.

Image: Debris Flow Damage in California
February 8, 2010

Debris Flow Damage in California

House damaged by debris flows generated in Mullally Canyon in response to a rainstorm on February 6, 2010. The drainage basin above this home was burned the previous summer by the Station Fire, the largest fire in the history of Los Angeles County.

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March 19, 2008

What is the greatest hazard presented by Mount Rainier?

Listen to hear the answer.

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Pinatubo Lahar Damage

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