Deschutes National Forest
1001 SW Emkay Drive
Bend, OR 97702
(541) 383-5300
Ochoco National Forest
3160 N.E. 3rd Street
Prineville, OR 97754
(541) 416-6500
Crooked River National Grassland
813 S.W. Hwy. 97
Madras, OR 97741
(541) 475-9272
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Geology
Oregon Volcanoes
Broken Top Volcano
SUMMARY
Type: stratovolcano
Activity: extinct
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
Topo
Map from TopoZone
Broken Top Photo Menu
GEOLOGIC BACKGROUND:
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
times.
- 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.
HISTORIC ACTIVITY:
DATA SOURCE:
ADDITIONAL INFORMATION
- Link to U.S.G.S. - CVO
- Link to U.S.G.S. Visit a Volcano Info for Broken
Top
- Link to University of Washington Geophysics Program Information
- Link to VolcanoWorld
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