The Montecito, California 2018 Debris Flows: Generation, Flow and Transport Properties, Sedimentation, and Fan Modification
Abstract
The 2018 Montecito debris flows occurred under ideal conditions for establishing some generalizable principles of debris-flow development after wildfire. After a wildfire de-vegetated several catchments in steep mountain terrain of the Santa Ynez Mountain Range, a short intense rainstorm travelling as a single band across the landscape triggered widespread mud generation by two dominant processes on shale and sandstone formations. Debris flows released from both rock types exhibited viscous behavior on the mountain slopes, recruited boulders from canyon bottoms, and grew in peak discharge and other flow properties as they converged on canyon mouths and spread onto piedmont fans. Various methods indicated super-critical flows in the canyons and upper fans, and speeds of 10 m/s behind a boulder-rich front, separated from the subsequent stony and viscous flows. Peak discharges over-taxed the conveyance capacity of the single channel crossing each fan, scouring the channels deeper and wider, and dispersing large boulders along the channels and overbank. The overbank boulder fields exhibited considerable size variability, but there was also a crude size sorting associated with systematic patterns of flow velocity across the depositional areas. The fluid matrix also dispersed along channels and across the fans to create distinctive spatial patterns of fan growth. Through field surveying and remote sensing we have been able to identify and quantify matrix generation mechanisms, patterns of boulder recruitment, debris-flow kinematics, patterns of boulder dispersal and of texture and rheological properties of flow materials collected from source areas to fan deposits.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP32A..01D
- Keywords:
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- 1824 Geomorphology: general;
- HYDROLOGYDE: 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1856 River channels;
- HYDROLOGYDE: 5419 Hydrology and fluvial processes;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS