USGS/Cascades Volcano Observatory, Vancouver, Washington
REPORT:
Debris Flow, Debris Avalanche, and Flood Hazards At and Downstream from Mount
Rainier, Washington
-- K.M. Scott and J.W. Vallance, 1995,
Debris Flow, Debris Avalanche, and Flood Hazards at and downstream from Mount
Rainier, Washington:
U.S. Geological Survey Hydrologic Investigations Atlas HA-729, 1:100,000
Abstract
Mount Rainier volcano has produced many large debris flows and debris avalanches
during the last 10,000 years. These flows have periodically traveled more than
100 kilometers from the volcano to inundate parts of the now-populated Puget
Sound Lowland. Meteorological floods also have caused damage, but future
effects will be partly mitigated by reservoirs.
Mount Rainier presents the most severe flow risks of any volcano in the United
States. Volcanic debris flows (lahars) are of two types: (1) cohesive,
relatively high clay flows originating as debris avalanches, and (2) noncohesive
flows with less clay that begin most commonly as meltwater surges. Three case
histories represent important subpopulations of flows with known magnitudes and
frequencies. The risks of each subpopulation may be considered for general
planning and design.
A regional map illustrates the extent of inundation by the case-history flows,
the largest of which originated as debris avalanches and moved from Mount
Rainier to Puget Sound. The paleohydrologic record of these past flows
indicates the potential of inundation by future flows from the volcano. a map
of the volcano and its immediate vicinity shows examples of smaller debris
avalanches and debris flows in the 20th century.
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11/22/02, Lyn Topinka