Evidence of Ancient Lake in California's Eel River Emerges
ScienceDaily (Nov. 14, 2011) — A catastrophic landslide 22,500 years ago dammed the upper reaches of northern California's Eel River, forming a 30-mile-long lake, which has since disappeared, and leaving a living legacy found today in the genes of the region's steelhead trout, report scientists at two West Coast universities.
View down the Eel River, with the reconstructed ancient lake surface in blue. (Credit: Ben Mackey, Caltech)
Using remote-sensing technology known as airborne Light Detection and Ranging (LiDAR) and hand-held global-positioning-systems (GPS) units, a three-member research team found evidence for a late Pleistocene, landslide-dammed lake along the river, about 60 miles southeast of Eureka.
The river today is 200 miles long, carved into the ground from high in the California Coast Ranges to its mouth in the Pacific Ocean in Humboldt County.
The evidence for the ancient landslide, which, scientists say, blocked the river with a 400-foot wall of loose rock and debris, is detailed this week in a paper appearing online ahead of print in theProceedings of the National Academy of Sciences.
The National Science Foundation-funded study provides a rare glimpse into the geological history of this rapidly evolving mountainous region.
It helps to explain emerging evidence from other studies that show a dramatic decrease in the amount of sediment deposited from the river in the ocean just off shore at about the same time period, says lead author Benjamin H. Mackey, who began the research while pursuing a doctorate earned in 2009 from the University of Oregon. He is now a postdoctoral researcher at the California Institute of Technology.
"Perhaps of most interest, the presence of this landslide dam also provides an explanation for the results of previous research on the genetics of steelhead trout in the Eel River," Mackey said, referring to a 1999 study by U.S. Forest Service researchers J.L. Nielson and M.C. Fountain. In their study, published in the journal Ecology of Freshwater Fish, they found a striking relationship in two types of ocean-going steelhead in the river -- a genetic similarity not seen among summer-run and winter-run steelhead in other nearby rivers.
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Landslide-dammed paleolake perturbs marine sedimentation and drives genetic change in anadromous fish
Benjamin H. Mackey a,1,2, Joshua J. Roering a, and Michael P. Lamb b
Author Affiliations
aDepartment of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403; and
bDivision of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125
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.
erosion, Franciscan mélange,genetic introgression
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@caltech.edu.
Author contributions: B.H.M. and J.J.R. designed research; B.H.M. performed research; B.H.M., J.J.R., and M.P.L. analyzed data; and B.H.M. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at
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