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Three Sisters is one of three potentially active
volcanic centers that lie close to rapidly growing
communities and resort areas in Central
Oregon. Two types of volcanoes exist in the
Three Sisters region and each poses distinct
hazards to people and property. South Sister,
Middle Sister, and Broken Top, major
composite volcanoes clustered near the center
of the region, have erupted repeatedly over tens
of thousands of years and may erupt
explosively in the future. In contrast, mafic
volcanoes, which range from small cinder cones
to large shield volcanoes like North Sister and
Belknap Crater, are typically short-lived
(weeks to centuries) and erupt less explosively
than do composite volcanoes. Hundreds of
mafic volcanoes scattered through the Three
Sisters region are part of a much longer zone
along the High Cascades of Oregon in which
birth of new mafic volcanoes is possible.
This report describes the types of hazardous
events that can occur in the Three Sisters region
and the accompanying volcano-hazard-zonation
map outlines areas that could be at risk from
such events.
-- Scott, et.al., 2001
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[Graphic,18K,InlineGIF]
