Fluvial sedimentation following Quaternary eruptions of Mount St. Helens, Washington
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.
- Research Organization:
- Geological Survey, Vancouver, WA (USA)
- OSTI ID:
- 6461570
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
Similar Records
Deposits of large volcanic debris avalanches at Mount St. Helens and Mount Shasta volcanoes
Impact of Mount St. Helens eruption on hydrology and water quality
Related Subjects
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)