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Erosional furrows formed during the lateral blast at Mount St. Helens, May 18, 1980

Kieffer, Susan Werner and Sturtevant, Bradford (1988) Erosional furrows formed during the lateral blast at Mount St. Helens, May 18, 1980. Journal of Geophysical Research B, 93 (B12). pp. 14793-14816. ISSN 0148-0227. doi:10.1029/JB093iB12p14793.

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Nearly horizontal, quasi-periodic erosional features of 7-m average transverse wavelength and of order 100-m length occur in scattered locations from 3.5 to 9 km from the crater at Mount St. Helens under deposits of the lateral blast of May 18, 1980. We attribute the erosional features to scouring by longitudinal vortices resulting from flow instabilities induced by complex topography, namely, by streamline curvature in regions of reattachment downstream of sheltered regions, and by the cross-flow component of flow subparallel to ridge crests. The diameter of the vortices and their transverse spacing, inferred from the distance between furrows, are taken to be of the order of the boundary layer thickness. The inferred boundary layer thickness (≈14 m at 9 km from the source of the blast) is consistent with the running length from the mountain to the furrow locations. By using knowledge of ablation patterns on bodies and lofting of dust in high-speed flow, we are able to infer some features of the flow field within the blast. Within the furrows the erosion rate was of the order of 9 kg m^(−2) s^(−1), about 4 times greater than that expected from laboratory data obtained in flow free of longitudinal vortices. The orientation of furrows induced by the cross-flow instability can be used to measure the upwash angle and estimate the flow Mach number: at the central ridge of Spirit Lake the Mach number is inferred to have been about 2.5, and the flow velocity approximately 235 m/s. The similarities and differences between the furrows reported here and channels observed at other volcanoes are discussed.

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Additional Information:Copyright 1988 by the American Geophysical Union. (Received November 11, 1987; accepted March 10, 1988.) Paper number 7B7170. We thank Harry Glicken, Richard Hoblitt, and Don Mullineaux for useful conversations, Hans Hornung and Michael Sheridan for penetrating reviews of the manuscript, and Ichiro Sugioka for assistance in surveying, data reduction, and preparation of the manuscript. This work was supported jointly by the National Science Foundation under grant EAR-8512724 and the U.S. Geological Survey. Approved by Director, U.S. Geological Survey, November 5, 1987.
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Issue or Number:B12
Record Number:CaltechAUTHORS:20141029-164352848
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Official Citation:Kieffer, S. W., and B. Sturtevant (1988), Erosional furrows formed during the lateral blast at Mount St. Helens, May 18, 1980, J. Geophys. Res., 93(B12), 14793–14816, doi:10.1029/JB093iB12p14793.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51040
Deposited By: George Porter
Deposited On:30 Oct 2014 16:43
Last Modified:10 Nov 2021 19:04

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