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
Middle Sister Volcano
SUMMARY
Type: stratovolcano
Activity: extinct
Last Eruption: estimated at about 50,000 yrs ago
Rock Type: predominantly basalt with andesite, dacite,
and rhyodacite.
Eruptive Volume: ?
Latitude: 44.15 N
Longitude: 121.78 W
Location Maps: from TIGER Mapping Service
Topo
Map from TopoZone
Middle Sister 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 younger than the North Sister and older than
the South Sister. It was active in late Pleistocene but not
postglacial time.
- 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:
RECENT ACTIVITY:
-
During the period from about 10 am on March 23, 2004 to about
1 am on March 25 a swarm of earthquake occurred in the Three
Sisters area. More than 100 small quake up to a magnitude of
1.9 occurred. Seismograms
of swarm.
-
On May 8, 2001, U.S. Geological Survey scientists reported
that by using Satellite
Radar Interferometry (or InSAR) they had detected a broad
area over which the ground has swelled upward slightly during
the past few years. The area is centered 5 kilometers
(3 miles) west of South Sister volcano in the Three Sisters
region of the central Oregon Cascade Range. The area of uplift
is about 15 to 20 kilometers (9 to 12 miles) in diameter and
the maximum amount of uplift at its center is about 10 centimeters
(4 inches).
DATA SOURCE:
ADDITIONAL INFORMATION
- Link to U.S.G.S. - CVO
- Link to U.S.G.S. Visit a Volcano Info for Three
Sisters
- Link to University of Washington Geophysics Program Information
- Link to VolcanoWorld
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