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Climate-change versus landslide origin of fill terraces in a rapidly eroding bedrock landscape: San Gabriel River, California

Scherler, Dirk and Lamb, Michael P. and Rhodes, Edward J. and Avouac, Jean-Philippe (2016) Climate-change versus landslide origin of fill terraces in a rapidly eroding bedrock landscape: San Gabriel River, California. Geological Society of America Bulletin, 128 (7-8). pp. 1228-1248. ISSN 0016-7606. doi:10.1130/B31356.1.

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Fill terraces along rivers represent the legacy of aggradation periods that are most commonly attributed to climate change. In the North Fork of the San Gabriel River, an arid bedrock landscape in the San Gabriel Mountains, California, a series of prominent fill terraces was previously related to climate-change−induced pulses of hillslope sediment supply that temporarily and repeatedly overwhelmed river transport capacity during the Quaternary. Based on field observations, digital topographic analysis, and dating of Quaternary deposits, we suggest instead that valley aggradation was spatially confined to the North Fork San Gabriel Canyon and was a consequence of the sudden supply of unconsolidated material to upstream reaches by one of the largest known landslides in the San Gabriel Mountains. New ^(10)Be-derived surface exposure ages from the landslide deposits, previously assumed to be early to middle Pleistocene in age, indicate at least three Holocene events at ca. 8−9 ka, ca. 4−5 ka, and ca. 0.5−1 ka. The oldest and presumably most extensive landslide predates the valley aggradation period, which is constrained by existing ^(14)C ages and new luminescence ages to ca. 7−8 ka. The spatial distribution, morphology, and sedimentology of the river terraces are consistent with deposition from far-traveling debris flows that originated within, and mined, the landslide deposits. Valley aggradation in the North Fork San Gabriel Canyon therefore resulted from locally enhanced sediment supply that temporarily overwhelmed river transport capacity, but the lack of similar deposits in other parts of the San Gabriel Mountains argues against a regional climatic signal. Our study highlights the potential for valley aggradation by debris flows in arid bedrock landscapes downstream of landslides that occupy headwater areas.

Item Type:Article
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URLURL TypeDescription
Scherler, Dirk0000-0003-3911-2803
Lamb, Michael P.0000-0002-5701-0504
Avouac, Jean-Philippe0000-0002-3060-8442
Additional Information:© 2016 Geological Society of America. Manuscript Received 24 May 2015; Revised Manuscript Received 29 December 2015; Manuscript Accepted 20 January 2016; First published online February 10, 2016. This project was supported by the Gordon and Betty Moore Foundation, through the Tectonics Observatory, National Science Foundation grant EAR- 0838495. Scherler was supported by a Feodor Lynen Scholarship through the Alexander von Humboldt Foundation. Lamb acknowledges support from the donors of the American Chemical Society Petroleum Research Fund. We thank two anonymous reviewers and the Associate Editor F. Pazzaglia for constructive comments that helped improving the paper. This work started as a Caltech class project, and we are thankful for help from the participants of Ge125.
Group:Caltech Tectonics Observatory
Funding AgencyGrant Number
Gordon and Betty Moore FoundationUNSPECIFIED
Alexander von Humboldt FoundationUNSPECIFIED
American Chemical Society Petroleum Research FundUNSPECIFIED
Issue or Number:7-8
Record Number:CaltechAUTHORS:20160323-110329270
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Official Citation:Dirk Scherler, Michael P. Lamb, Edward J. Rhodes, and Jean-Philippe Avouac Climate-change versus landslide origin of fill terraces in a rapidly eroding bedrock landscape: San Gabriel River, California Geological Society of America Bulletin, July 2016, v. 128, no. 7-8, p. 1228-1248, first published on February 10, 2016, doi:10.1130/B31356.1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:65622
Deposited By: Tony Diaz
Deposited On:25 Mar 2016 18:49
Last Modified:10 Nov 2021 23:48

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