Cascades Volcano Observatory, Vancouver, Washington

Three Sisters, Oregon

Sisters85_aerial_three_sisters_oregon_09-85.jpg Aerial view, the Three Sisters volcanoes in Oregon, from the south looking north. Left to right -- South Sister, Middle Sister, and North Sister. USGS Photograph taken in September 1985 by Lyn Topinka. [medium size] ... [large size] ... [TIF Format, 18 M]

• 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

• 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.

[Map,20K,InlineGIF]
Major West Coast Volcanoes - Washington, Oregon, and California
-- Graphic by: Lyn Topinka, 1998

[Map,20K,InlineGIF]
Bend/Sisters/Santiam Pass/McKenzie Pass Area
-- Modified from: Taylor, Oregon State University, 1981, USGS Circular 838

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