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The role of waterfalls and knickzones in controlling the style and pace of landscape adjustment in the western San Gabriel Mountains, California

DiBiase, Roman A. and Whipple, Kelin X. and Lamb, Michael P. and Heimsath, Arjun M. (2015) The role of waterfalls and knickzones in controlling the style and pace of landscape adjustment in the western San Gabriel Mountains, California. Geological Society of America Bulletin, 127 (3-4). pp. 539-559. ISSN 0016-7606.

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Bedrock rivers set the pace of landscape adjustment to tectonic and climatic forcing by transmitting signals of base-level change upstream through the channel network and ultimately to hillslopes. River incision is typically modeled as a monotonic function of bed shear stress or stream power, modulated by sediment tools and cover effects, but these models do not apply in channels with steep or vertical bedrock reaches due to changes in flow dynamics, hydraulic geometry, and bed cover. Here, we investigate how such knickzones (oversteepened channel reaches often containing waterfalls) influence the propagation of slope-break knickpoints that separate relict from adjusting topography, and thus the response times of landscapes to external forcing. We use a conceptual long-profile model to explore the consequences of waterfalls and knickzones on channel response and compare predictions to light detection and ranging (LiDAR) topography, field observations, and cosmogenic radionuclide data from Big Tujunga Creek, a 300 km2 watershed in the San Gabriel Mountains, California. Three prominent knickzones along Big Tujunga Creek, characterized by numerous waterfalls, show contrasting behavior. For the upper knickzone, waterfalls align with bands of harder rock exposed on adjacent hillslopes, and between waterfalls, the channel is mantled by large (>2 m) boulders, indicating knickzone retreat is slow compared to predictions of slope-break knickpoint retreat from stream-power models, enhancing the preservation of an upstream relict landscape. The middle knickzone shows evidence for both fast and slow knickzone retreat, as well as significant deviations from predictions of uniform tributary knickpoint elevations derived from stream-power models. The lower knickzone is characterized by a waterfall and knickzone within an incised inner gorge that provide evidence of rapid retreat relative to background channel incision. Overall, we find a pattern of decreasing knickzone and waterfall retreat rate with distance upstream of the range front, beyond decreases predicted by simple area-dependent celerity models. Our results highlight that waterfalls and knickzones can both enhance and inhibit landscape adjustment, leading to divergent controls on the pace of landscape evolution.

Item Type:Article
Related URLs:
URLURL TypeDescription DOIArticle
DiBiase, Roman A.0000-0002-5347-8396
Whipple, Kelin X.0000-0002-8430-6925
Lamb, Michael P.0000-0002-5701-0504
Additional Information:© 2014 Geological Society of America. Manuscript Received 9 April 2014. Revised Manuscript Received 30 July 2014. Manuscript Accepted 5 September 2014. First published on October 22, 2014. Science Editor: A. Hope Jahren; Associate Editor: Anne Jefferson. We thank B. Adams, N. Gasparini, M. Jungers, and D. Stolar for intrepid field assistance, and J. Scheingross and L. Malatesta for valuable discussions and feedback. Comments from two anonymous reviewers and the associate editor helped improve the manuscript. Funding for this project was provided by the National Science Foundation Geomorphology and Land Use Dynamics program (EAR-0724194 to Whipple, EAR-0518998 to Heimsath, and EAR-1147381 to Lamb). Laser altimetry data were acquired and processed by the National Center for Airborne Laser Mapping (NCALM) with support from Arizona State University (Whipple and Heimsath), Caltech (Lamb), and the U.S. Geological Survey.
Funding AgencyGrant Number
Arizona State UniversityUNSPECIFIED
Issue or Number:3-4
Record Number:CaltechAUTHORS:20150507-094505136
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Official Citation:Roman A. DiBiase, Kelin X Whipple, Michael P. Lamb, and Arjun M. Heimsath The role of waterfalls and knickzones in controlling the style and pace of landscape adjustment in the western San Gabriel Mountains, California Geological Society of America Bulletin, March 2015, v. 127, p. 539-559, First published on October 22, 2014, doi:10.1130/B31113.1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57325
Deposited By: Ruth Sustaita
Deposited On:07 May 2015 19:33
Last Modified:09 Mar 2020 13:19

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