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Three Sisters

Find U.S. Volcano

The three aligned stratovolcanoes of North, Middle, and South Sister are closely spaced, but they display very little family resemblance.

Quick Facts

Location: Oregon, Lane County

Latitude: 44.103° N

Longitude: 121.768° W

Elevation: 3,157 (m) 10,358 (f)

Volcano type: Complex volcano

Composition: Andesite to Rhyolite

Most recent eruption: 2,000 years ago

Threat Potential: Very High*

*based on the National Volcano Early Warning System

Summary

"For magnificence of glacial scenery, for wealth of recent lavas, and for graphic examples of dissected volcanoes, no part of this range surpasses the area embracing the Sisters and McKenzie Pass." - Volcanologist Howel Williams, 1944

The three aligned stratovolcanoes of North, Middle, and South Sister are closely spaced, but they display very little family resemblance. North Sister is solely composed of basalt to andesite and is at least 120,000 years old. Middle Sister was built between 40 and 14 ka of magma ranging from basalt to dacite, with minor high-silica rhyolite. South Sister, composed of andesite to rhyolite, is the most silicic of all the cones and was constructed between 50 and 2 ka. The most recent eruptions were of rhyolite near South Sister, about 2,000 years ago. Scientific and public interest in the Three Sisters volcanic cluster was heightened in 2001 when scientists recognized that a phase of uplift had started in 1997 within a broad area about 6 km west of South Sister.

The Three Sisters lie within a broad area of densely spaced volcanic vents that, in the Cascades, is duplicated only in southern Washington and Northern California. The Sisters reach of the Cascade arc contains at least 466 volcanoes that erupted within the past one million years, and most are small single-eruption volcanic vents, though there are a few are low shields and stratocones such as Broken Top.

News

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Scientists detect rejuvenated uplift near South Sister volcano.

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Which U.S. volcanoes pose a threat?

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Geologic maps lay the foundation for this virtual tour of western states volcanoes.

Publications

2018 update to the U.S. Geological Survey national volcanic threat assessment

When erupting, all volcanoes pose a degree of risk to people and infrastructure, however, the risks are not equivalent from one volcano to another because of differences in eruptive style and geographic location. Assessing the relative threats posed by U.S. volcanoes identifies which volcanoes warrant the greatest risk-mitigation efforts by the U.S. Geological Survey and its partners. This update

Authors
John W. Ewert, Angela K. Diefenbach, David W. Ramsey

Science

Hazards Summary for Three Sisters

Three Sisters is a potentially active volcanic center that lies close to rapidly growing communities and resort areas in Central Oregon.
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Hazards Summary for Three Sisters

Three Sisters is a potentially active volcanic center that lies close to rapidly growing communities and resort areas in Central Oregon.
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Lava Flow Hazards at Three Sisters

Volcanoes in the Three Sisters region have erupted a wide variety of magma types, therefore the shape, size, and impact of future lava flows could vary greatly.
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Lava Flow Hazards at Three Sisters

Volcanoes in the Three Sisters region have erupted a wide variety of magma types, therefore the shape, size, and impact of future lava flows could vary greatly.
Learn More

Tephra Fall Hazards at Three Sisters

Eruptions from any volcano in the Three Sisters region, as well as from more distant volcanoes in the Cascade Range, are sources of potential tephra fall in Central Oregon communities.
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Tephra Fall Hazards at Three Sisters

Eruptions from any volcano in the Three Sisters region, as well as from more distant volcanoes in the Cascade Range, are sources of potential tephra fall in Central Oregon communities.
Learn More