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Drainage evolution in the debris avalanche deposits near Mount Saint Helens, WashingtonThe 18 May 1980 eruption of Mount St. Helens was initiated by a massive rockslide-debris avalanche which completely transformed the upper 25 km of the North Fork Toutle River valley. The debris was generated by one of the largest gravitational mass movements ever recorded on Earth. Moving at an average velocity of 35 m/s, the debris avalanche buried approximately 60 sq km of terrain to an average depth of 45 m with unconsolidated, poorly sorted volcaniclastic material, all within a period of 10 minutes. Where exposed and unaltered by subsequent lahars and pyroclastic flows, the new terrain surface was characterized predominantly by hummocks, closed depressions, and the absence of an identifiable channel network. Following emplacement of the debris avalanche, a complex interrelationship of fluvial and mass wasting processes immediately began operating to return the impacted area to an equilibrium status through the removal of material (potential energy) and re-establishment of graded conditions. In an attempt to chronicle the morphologic evolution of this unique environmental setting, a systematic series of interpretative maps of several selected areas was produced. These maps, which document the rate and character of active geomorphic processes, are discussed.
Document ID
19840015428
Acquisition Source
Legacy CDMS
Document Type
Other - Other
Authors
Beach, G. L.
(Geological Survey Vancouver, WA, United States)
Dzurisin, D.
(Geological Survey Vancouver, WA, United States)
Date Acquired
August 12, 2013
Publication Date
April 1, 1984
Publication Information
Publication: NASA. Washington Rept. of Planetary Geol. Programs
Subject Category
Geophysics
Accession Number
84N23496
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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