Aerial view of the Three Sisters Volcanoes, Central Oregon,
showing (left to right), South Sister, Middle Sister, and North Sister
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Three Sisters and Vicinity
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Three Sisters Volcanoes
-- Geographic Setting, Geologic and Eruptive History
The Three Sisters area contains 5 large cones of Quaternary age--
North Sister,
Middle Sister,
South Sister,
Broken Top, and
Mount Bachelor.
North Sister and Broken Top
are deeply dissected and probably have been inactive
for at least 100,000 years.
Middle Sister is younger than North Sister,
and 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.
-- Excerpt from:
Hoblitt, Miller, and Scott, 1987,
Volcanic Hazards with Regard to Siting Nuclear-Power Plants
in the Pacific Northwest:
USGS Open-File Report 87-297
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Field Trip Guide to the Central Oregon High Cascades
-- Scott and Gardner, 1990
This field excursion to the central Oregon High Cascades highlights
aspects of Quaternary volcanic and glacial history in the vicinity of
Mount Bachelor (formerly Bachelor Butte) and South Sister.
Part 2 (Bend Area) portion of the field excursion to the central Oregon High
Cascades highlights aspects of the ash-flow tuffs in the Bend area. The guide
contains brief descriptions of the stops, and some of the key features and
interpretations of the stops are discussed further in the paper by Hill and
Taylor at the end of the guide.
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The Pacific Crest Trail crosses the west base of the Three Sisters from a northern trailhead at
McKenzie Pass (Oregon 242) and a southern trailhead at Devils Lake (Cascade Lakes Highway).
-- Excerpt from: Wood and Kienle, 1990,
Volcanoes of North America: United States and Canada:
Cambridge University Press, 354p., p.184-185, Contribution by Edward M. Taylor
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[Map,20K,InlineGIF]
Major West Coast Volcanoes - Washington, Oregon, and California
-- Graphic by: Lyn Topinka, 1998
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[Map,20K,InlineGIF]
Bend/Sisters/Santiam Pass/McKenzie Pass Area
-- Modified from: Taylor, Oregon State University, 1981,
USGS Circular 838
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Deschutes National Forest
-- Link courtesy U. S. Forest Service
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Willamette National Forest
-- Link courtesy U. S. Forest Service
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MORE Useful Sites
-- CVO Menu, includes links to Volcano Info, Seismicity, Hydrology, etc.
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-- CVO Menu, includes links to Weather Forecasts, DOT's, Pass Reports, etc.
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Three Sister Volcanoes Menu
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