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Evidence for superelevation, channel incision, and formation of cyclic steps by turbidity currents in Eel Canyon, California

Lamb, Michael P. and Parsons, Jeffrey D. and Mullenbach, Beth L. and Finlayson, David P. and Orange, Daniel L. and Nittrouer, Charles A. (2008) Evidence for superelevation, channel incision, and formation of cyclic steps by turbidity currents in Eel Canyon, California. Geological Society of America Bulletin, 120 (3-4). pp. 463-475. ISSN 0016-7606. doi:10.1130/B26184.1.

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We performed a multibeam survey of Eel Canyon, offshore northern California. The survey revealed a significant bend in the canyon that appears to be due to the oblique compressional tectonics of the region. A series of steps within a linear depression, similar to 280 m above the canyon floor, extends from the canyon rim at this bend to the subduction zone and a distinct fan-like topographic rise. We hypothesize that the linear depression is a distributary channel and the steps are cyclic-step bedforms created by turbidity currents. Our interpretation indicates that turbidity currents are able to run up and overspill the 280-m-high canyon wall, resulting in a partial avulsion of the canyon and the construction of a fan lobe that is offset from the canyon mouth. Simple hydraulic calculations show that turbidity currents generated in the canyon head from failure of 2-3 m of material would be capable of partially overflowing the canyon at this bend, assuming steady-uniform flow, full conversion of the failed mass into a turbidity current, and a range of friction coefficients. These estimates are consistent with analyses of sediment cores collected in the head of Eel Canyon, which suggest that 2-3 m of material fails on decadal time scales. Our calculations show that the overflowing parts of the currents would have large shear velocities (>10 cm/s) and supercritical Froude numbers, consistent with erosion of the distributary channel and formation of cyclic steps by turbidity currents.

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Lamb, Michael P.0000-0002-5701-0504
Additional Information:© 2007 Geological Society of America. Manuscript received 23 January 2007. Revised manuscript received 19 July 2007. Manuscript accepted 29 August 2007. This study was funded by Office of Naval Research grant N000149910028 and National Undersea Research Program grant UAF(WA-00–05). Norman Maher helped plan the bathymetric survey. We thank Wayne McCool, John Crockett, David Drake, and Leda Beth Gray for assisting on the cruise. Rob Hagg helped ensure the success in later stages of the cruise by supplying us with on-the-fly imagery of the canyon. Tina Lomnicky aided in post-processing of the multibeam data. Paul Heller, Roger Slatt, John Warme, and Gerilyn Soreghan provided helpful reviews of an earlier draft. Paul Heller and Carlos Pirmez provided constructive reviews of this manuscript. Gary Parker inspired our interpretation of the cyclic steps.
Funding AgencyGrant Number
Office of Naval Research (ONR)N000149910028
National Undersea Research ProgramUAF(WA-00–05)
Subject Keywords:submarine canyons; Eel River; turbidity currents; cyclic steps; channel formation; superelevation; avulsion
Issue or Number:3-4
Record Number:CaltechAUTHORS:LAMgsab08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13380
Deposited By: Tony Diaz
Deposited On:29 Apr 2009 21:57
Last Modified:08 Nov 2021 22:37

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