Deschutes National Forest
1001 SW Emkay Drive
Bend, OR 97702
Ochoco National Forest
3160 N.E. 3rd Street
Prineville, OR 97754
Crooked River National Grassland
813 S.W. Hwy. 97
Madras, OR 97741
Broken Top Volcano
Last Eruption: estimated at about 100,000 yrs ago
Rock Type: predominantly basaltic andesite with interbedded
andesite, dacite, and rhyodacite.
Eruptive Volume: ?
Latitude: 44.08 N
Longitude: 121.70 W
Location Maps: from TIGER Mapping Service
Map from TopoZone
Broken Top Photo Menu
The Three Sisters area contains 4 large cones of Quaternary age
-- North Sister, Middle Sister, South Sister, and Broken Top.
- North Sister and Broken Top are deeply dissected and probably
have been inactive for at least 100,000 years.
- Middle Sister and South Sister are younger than the North Sister.
They have both been erupting over the last 50,000 years.
- Middle Sister was active in late Pleistocene but not postglacial
- South Sister is the least dissected; its basaltic andesite summit
cone has a well preserved crater. Most of South Sister predates
late Wisconsin glaciation and is therefore older than 25,000 years;
however, eruptions of rhyolite from flank vents have occurred
as recently as 2000 years ago.
- Link to U.S.G.S. - CVO
- Link to U.S.G.S. Visit a Volcano Info for Broken
- Link to University of Washington Geophysics Program Information
- Link to VolcanoWorld