The Influence of Frost Weathering on Debris Flow Sediment Supply in an Alpine Basin

• Published in: Journal of geophysical research. Earth surface 2020-02, Vol.125 (2), p.n/a
• Main Authors: Rengers, F. K., Kean, Jason W., Reitman, Nadine G., Smith, Joel B., Coe, Jeffrey A., McGuire, Luke A.
• Format: Article
• Language: English
• Subjects: Accumulation; Cliffs; Convective storms; Debris flow; Detritus; erosion; Flow channels; Frost; Low temperature; Mass balance; Mass wasting; Mountains; Overland flow; Refilling; Rock falls; Rockfall; Sediment; Sedimentation; Sedimentation & deposition; Sediments; Storms; Surface runoff; Watersheds; Weathering
• ISSN: 2169-9003; 2169-9011
• DOI: 10.1029/2019JF005369

Rocky, alpine mountains are prone to mass wasting from debris flows. The Chalk Cliffs study area (central Colorado, USA) produces debris flows annually. These debris flows are triggered when overland flow driven by intense summer convective storms mobilizes large volumes of sediment within the channel network. Understanding the debris flow hazard in this, and similar alpine settings, requires determining the magnitude of sediment accumulation between debris flow seasons and identifying the control on sediment production. To address these knowledge gaps, we measured changes in sediment production using a sediment retention fence to quantify how sedimentation was influenced by temperature at the plot scale. These measurements were extrapolated to a larger area, where we extended the sediment fence results to explore how rockfall sedimentation contributed to channel refilling between active debris flow periods. This work shows that debris flow channel refilling is correlated with low temperatures and time in the frost‐cracking window, implicating frost‐weathering mechanisms as a key driver of sedimentation. This sediment production process resulted in a large amount of sediment accumulation during a single winter season in our study reach (up to 0.4 m in some locations). Using these observations, we develop a channel refilling model that generally describes the mass balance of debris flow watersheds in alpine areas. Key Points Frost weathering of bedrock cliffs during cold temperatures reloads debris flows channels with sediment We quantify relations between sediment production and measured temperatures Temperature‐sediment production relations provide a foundation for forecasts and hindcasts of debris flow sediment supply