Mount Rainier, the highest peak in the Cascade Range at 4,392m (14,410 ft), forms a dramatic backdrop to the Puget Sound region. During an eruption 5,600 years ago the once-higher
edifice 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 cave beneath the summit icecap.
Location: Washington, Pierce County
Latitude: 46.853° N
Longitude: 121.76° W
Elevation:
4,393 (m)
14,412 (f)
Volcano type: Stratovolcano
Composition: andesite, dacite
Most recent eruption: ∼1,000 years ago
Nearby towns: Orting, Seattle, Tacoma, Yakima
Alert Level: Normal