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Spatial patterns of erosion in a bedrock gorge
Author(s) -
Beer Alexander. R.,
Turowski Jens M.,
Kirchner James W.
Publication year - 2017
Publication title -
journal of geophysical research: earth surface
Language(s) - English
Resource type - Journals
eISSN - 2169-9011
pISSN - 2169-9003
DOI - 10.1002/2016jf003850
Subject(s) - bedrock , geology , erosion , geomorphology , sediment , hydrology (agriculture) , abrasion (mechanical) , channel (broadcasting) , plucking , geotechnical engineering , mechanical engineering , electrical engineering , engineering
Understanding the physical processes driving bedrock channel formation is essential for interpreting and predicting the evolution of mountain landscapes. Here we analyze bedrock erosion patterns measured at unprecedented spatial resolution (mm) over 2 years in a natural bedrock gorge. These spatial patterns show that local bedrock erosion rates depend on position in the channel cross section, height above the streambed, and orientation relative to the main streamflow and sediment path. These observations are consistent with the expected spatial distribution of impacting particles (the tools effect) and shielding by sediment on the bed (the cover effect). Vertical incision by bedrock abrasion averaged 1.5 mm/a, lateral abrasion averaged 0.4 mm/a, and downstream directed abrasion of flow obstacles averaged 2.6 mm/a. However, a single plucking event locally exceeded these rates by orders of magnitude (∼100 mm/a), and accounted for one third of the eroded volume in the studied gorge section over the 2 year study period. Hence, if plucking is spatially more frequent than we observed in this study period, it may contribute substantially to long‐term erosion rates, even in the relatively massive bedrock at our study site. Our observations demonstrate the importance of bedrock channel morphology and the spatial distribution of moving and static sediment in determining local erosion rates.