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Title: Fluvial sedimentation following Quaternary eruptions of Mount St. Helens, Washington

Abstract

Depositional records of convulsive volcanic events at Mount St. Helens are in many places obscured by rapid fluvial erosion and deposition close to the volcano. Some major eruptions are recorded primarily by lahars and alluvium deposited tens of kilometers away. About 35 percent of the distinctive hummocky topography of the 1980 North Fork Toutle debris avalanche deposit now resembles an alluvial fan or a braided glacial outwash plain covered with 10 m or more of alluvium. Deposits of small (20 x 10/sup 6/m/sup 3/) but damaging lahars, such as those generated in the afternoon of 18 May 1980 and on 19 March 1982, have been largely eroded away. Rivers draining rapidly eroding areas surrounding Mount St. Helens presently have sediment yields that are among the highest in the world for nonglaciated streams of comparable size. These sediment loads are capable of causing aggradation-induced flooding in populated areas along the lower Toutle and Cowlitz Rivers. Sediment retention structures and dredging have prevented such flooding. Immediately following prehistoric eruptions, however, coarse-grained volcanic alluvium was deposited in the Cowlitz River to levels more than 1 m above the 1980 mud flow inundation level. Post-1980 rapid landscape modifications and high sediment yields are noteworthymore » because the eruption-impact area has not yet had a major regional storm and potentially catastrophic breachings of avalanche-impounded lakes have been prevented through engineering measures.« less

Authors:
;
Publication Date:
Research Org.:
Geological Survey, Vancouver, WA (USA)
OSTI Identifier:
6461570
Report Number(s):
CONF-8510489-
Journal ID: CODEN: GAAPB
Resource Type:
Conference
Journal Name:
Geol. Soc. Am., Abstr. Programs; (United States)
Additional Journal Information:
Journal Volume: 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; ALLUVIAL DEPOSITS; DEPOSITION; MT ST HELENS; ERUPTION; EROSION; QUATERNARY PERIOD; RIVERS; RUNOFF; SEDIMENTATION; SEDIMENTS; VOLCANOES; CASCADE MOUNTAINS; CENOZOIC ERA; ENVIRONMENTAL TRANSPORT; FEDERAL REGION X; GEOLOGIC AGES; GEOLOGIC DEPOSITS; MASS TRANSFER; MOUNTAINS; NORTH AMERICA; STREAMS; SURFACE WATERS; USA; WASHINGTON; 580202* - Geophysics- Volcanology- (1980-1989); 580100 - Geology & Hydrology- (-1989)

Citation Formats

Janda, R J, and Meyer, D F. Fluvial sedimentation following Quaternary eruptions of Mount St. Helens, Washington. United States: N. p., 1985. Web.
Janda, R J, & Meyer, D F. Fluvial sedimentation following Quaternary eruptions of Mount St. Helens, Washington. United States.
Janda, R J, and Meyer, D F. 1985. "Fluvial sedimentation following Quaternary eruptions of Mount St. Helens, Washington". United States.
@article{osti_6461570,
title = {Fluvial sedimentation following Quaternary eruptions of Mount St. Helens, Washington},
author = {Janda, R J and Meyer, D F},
abstractNote = {Depositional records of convulsive volcanic events at Mount St. Helens are in many places obscured by rapid fluvial erosion and deposition close to the volcano. Some major eruptions are recorded primarily by lahars and alluvium deposited tens of kilometers away. About 35 percent of the distinctive hummocky topography of the 1980 North Fork Toutle debris avalanche deposit now resembles an alluvial fan or a braided glacial outwash plain covered with 10 m or more of alluvium. Deposits of small (20 x 10/sup 6/m/sup 3/) but damaging lahars, such as those generated in the afternoon of 18 May 1980 and on 19 March 1982, have been largely eroded away. Rivers draining rapidly eroding areas surrounding Mount St. Helens presently have sediment yields that are among the highest in the world for nonglaciated streams of comparable size. These sediment loads are capable of causing aggradation-induced flooding in populated areas along the lower Toutle and Cowlitz Rivers. Sediment retention structures and dredging have prevented such flooding. Immediately following prehistoric eruptions, however, coarse-grained volcanic alluvium was deposited in the Cowlitz River to levels more than 1 m above the 1980 mud flow inundation level. Post-1980 rapid landscape modifications and high sediment yields are noteworthy because the eruption-impact area has not yet had a major regional storm and potentially catastrophic breachings of avalanche-impounded lakes have been prevented through engineering measures.},
doi = {},
url = {https://www.osti.gov/biblio/6461570}, journal = {Geol. Soc. Am., Abstr. Programs; (United States)},
number = ,
volume = 17,
place = {United States},
year = {Tue Jan 01 00:00:00 EST 1985},
month = {Tue Jan 01 00:00:00 EST 1985}
}

Conference:
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