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Crater Lake National Park is visited by about
500,000 people each year, with heaviest use during the
summer months. Crater Lake partially fills a type of
volcanic depression called a caldera that formed by
collapse of a 12,000 foot volcano known as Mount
Mazama during an enormous pyroclastic eruption
approximately 7,700 years ago. Although this Cascade
volcano does not directly threaten large population
centers, it does pose a hazard to facilities and people at
Crater Lake National Park and to the major
transportation corridor east of the Cascades. The
ultimate causes of volcanic activity at all Cascade
volcanic centers are linked by common processes.
However, Crater Lake is unique in many regards, and
potential effects of future activity cannot be anticipated
by analogy with past eruptions there or at other Cascade
volcanoes. Profound changes occurred at Crater Lake
about 7,700 years ago that affect the type of eruptions
that can occur and the consequences of such events for
the surrounding area. This report attempts to forecast
what may happen in such future, but largely
unprecedented events.
Volcanic eruptions are not the only geologic
hazards at Crater Lake. The Crater Lake region is cut
by many faults, some of which are capable of producing
damaging earthquakes (e.g., Klamath Falls, September
1993). Not only do earthquakes pose direct hazards to
people and structures but they also can cause rockfalls
and landslides which, if they entered the lake rapidly,
could produce life-threatening waves. Consequently,
this report contains information about faults, seismicity,
and possible effects of earthquake shaking in addition
to an evaluation of volcano hazards.
-- Bacon, et.al., 1997
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