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Landslide-dammed paleolake perturbs marine sedimentation and drives genetic change in anadromous fish

  1. Michael P. Lambb
  1. aDepartment of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403; and
  2. bDivision of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125
  1. Edited by Thomas Dunne, University of California, Santa Barbara, CA, and approved September 15, 2011 (received for review June 27, 2011)

Abstract

Large bedrock landslides have been shown to modulate rates and processes of river activity by forming dams, forcing upstream aggradation of water and sediment, and generating catastrophic outburst floods. Less apparent is the effect of large landslide dams on river ecosystems and marine sedimentation. Combining analyses of 1-m resolution topographic data (acquired via airborne laser mapping) and field investigation, we present evidence for a large, landslide-dammed paleolake along the Eel River, CA. The landslide mass initiated from a high-relief, resistant outcrop which failed catastrophically, blocking the Eel River with an approximately 130-m-tall dam. Support for the resulting 55-km-long, 1.3-km3 lake includes subtle shorelines cut into bounding terrain, deltas, and lacustrine sediments radiocarbon dated to 22.5?ka. The landslide provides an explanation for the recent genetic divergence of local anadromous (ocean-run) steelhead trout (Oncorhynchus mykiss) by blocking their migration route and causing gene flow between summer run and winter run reproductive ecotypes. Further, the dam arrested the prodigious flux of sediment down the Eel River; this cessation is recorded in marine sedimentary deposits as a 10-fold reduction in deposition rates of Eel-derived sediment and constitutes a rare example of a terrestrial event transmitted through the dispersal system and recorded offshore.

Footnotes

  • ?1Current address: Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125.

  • ?2To whom correspondence should be addressed. E-mail: bmackey{at}caltech.edu.

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