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Mount Rainier, the highest peak in the Cascade Range at 4,392m (14,410 ft), forms a dramatic backdrop to the Puget Sound region.


Summary

During an eruption 5,600 years ago the once-higher edifice of Mount Rainier collapsed to form a large crater open to the northeast much like that at Mount St. Helens after 1980. Ensuing eruptions rebuilt the summit, filling the large collapse crater. Large lahars (volcanic mudflows) from eruptions and from collapses of this massive, heavily glaciated andesitic volcano have reached as far as the Puget Sound lowlands. Since the last ice age, several dozen explosive eruptions spread tephra (ash, pumice) across parts of Washington. The last magmatic eruption was about 1,000 years ago. Extensive hydrothermal alteration of the upper portion of the volcano has contributed to its structural weakness promoting collapse. An active thermal system driven by magma deep under the volcano has melted out a labyrinth of steam caves beneath the summit icecap.

News

Date published: October 16, 2020

Media Advisory: Exclusive Interview Opportunities with Interior Officials to Learn about New Mt. Rainier Lahar Detection Stations

TACOMA, Wash. — What is a lahar and why are they a threat to those who live below Mount Rainier? Journalists are invited to learn about the  threat potential posed by lahars from Mount Rainier to local communities and how  new  USGS lahar monitoring stations will integrate into emergency preparedness and response.    

Date published: October 5, 2020

Opportunity for public comment on proposal to expand the lahar detection system within Mount Rainier National Park

Public input will be accepted from October 5-30, 2020 on a proposal to expand the lahar detection system inside Mount Rainier National Park.  

Date published: December 19, 2019

Earthquakes occur in Mount Rainier's hydrothermal system.

While the seismicity represents a temporary uptick in activity, Mount Rainier remains at normal, background levels of activity.

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