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Debris flow initiation from ravel-filled channel bed failure following wildfire in a bedrock landscape with limited sediment supply

Palucis, Marisa C. and Ulizio, Thomas P. and Lamb, Michael P. (2021) Debris flow initiation from ravel-filled channel bed failure following wildfire in a bedrock landscape with limited sediment supply. Geological Society of America Bulletin, 133 (9-10). pp. 2079-2096. ISSN 0016-7606. doi:10.1130/B35822.1.

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Steep, rocky landscapes often produce large sediment yields and debris flows following wildfire. Debris flows can initiate from landsliding or rilling in soil-mantled portions of the landscape, but there have been few direct observations of debris flow initiation in steep, rocky portions of the landscape that lack a thick, continuous soil mantle. We monitored a steep, first-order catchment that burned in the San Gabriel Mountains, California, USA. Following fire, but prior to rainfall, much of the hillslope soil mantle was removed by dry ravel, exposing bedrock and depositing ∼0.5 m of sandy sediment in the channel network. During a one-year recurrence rainstorm, debris flows initiated in the channel network, evacuating the accumulated dry ravel and underlying cobble bed, and scouring the channel to bedrock. The channel abuts a plowed terrace, which allowed a complete sediment budget, confirming that ∼95% of sediment deposited in a debris flow fan matched that evacuated from the channel, with a minor rainfall-driven hillslope contribution. Subsequent larger storms produced debris flows in higher-order channels but not in the first-order channel because of a sediment supply limitation. These observations are consistent with a model for post-fire ravel routing in steep, rocky landscapes where sediment was sourced by incineration of vegetation dams—following ∼30 years of hillslope soil production since the last fire—and transported downslope by dry processes, leading to a hillslope sediment-supply limitation and infilling of low-order channels with relatively fine sediment. Our observations of debris flow initiation are consistent with failure of the channel bed alluvium due to grain size reduction from dry ravel deposits that allowed high Shields numbers and mass failure even for moderate intensity rainstorms.

Item Type:Article
Related URLs:
URLURL TypeDescription
Palucis, Marisa C.0000-0003-0034-5810
Ulizio, Thomas P.0000-0001-9685-2926
Lamb, Michael P.0000-0002-5701-0504
Additional Information:© 2021 Geological Society of America. Manuscript Received 8 July 2020; Revised Manuscript Received 3 December 2020; Manuscript Accepted 16 December 2020. We thank Brian Zdeb and Brian Fuller for their help with setting up and collecting field data as well as Jason Kean for useful discussions on debris flow occurrence in the region and for sharing precipitation data from the nearby USGS rain gage. Funding was provided to M.P. Lamb by National Science Foundation grants EAR-1349115 and EAR-1558479 and to M.C. Palucis by National Science Foundation Postdoctoral Fellowship grant EAR-1452337. We thank the reviewers for their time and insightful comments, which helped to improve this manuscript.
Funding AgencyGrant Number
NSF Postdoctoral FellowshipEAR-1452337
Issue or Number:9-10
Record Number:CaltechAUTHORS:20210202-080123375
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Official Citation:Marisa C. Palucis, Thomas P. Ulizio, Michael P. Lamb; Debris flow initiation from ravel-filled channel bed failure following wildfire in a bedrock landscape with limited sediment supply. GSA Bulletin 2021; 133 (9-10): 2079–2096. doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107845
Deposited By: Tony Diaz
Deposited On:02 Feb 2021 16:27
Last Modified:16 Nov 2021 19:06

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