Mechanisms for avulsion on alluvial fans: insights from high-frequency topographic data

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Anya Leenman , Brett Eaton 


Avulsion is a key process in building alluvial fans, but it is also a formidable natural hazard. Based on laboratory experiments monitored with novel high-frequency photogrammetry, we present a new model for avulsion on widely graded gravel fans. Previous experimental studies of alluvial fans have suggested that avulsion occurs in a periodic autogenic cycle, that is thought to be mediated by the gradient of the fan and fan-channel. However, these studies measured gradients at low spatial or temporal resolutions, which capture temporally or spatially averaged topographic evolution. Here, we present high-resolution (1 mm), high-frequency (1-minute) topographic data and orthophotos from an alluvial fan experiment. Avulsions in the experiment were rapid and, in contrast to some previous experimental studies, avulsion occurrence was aperiodic. Moreover, we found little evidence of the back-filling observed at coarser temporal and spatial resolutions. Our observations suggest that avulsion is disproportionately affected by sediment accumulation in the channel, particularly around larger, less mobile grains. Such in-channel deposition can cause channel shifting that interrupts the autogenic avulsion cycle, so that avulsions are aperiodic and their timing is more difficult to predict.



Earth Sciences, Geomorphology, Physical Sciences and Mathematics


Experimental Geomorphology, Structure-from-Motion photogrammetry, Large grains


Published: 2020-12-17 21:32

Last Updated: 2021-01-18 20:43

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CC BY Attribution 4.0 International

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Data Availability (Reason not available):
The data used in this paper exceeds 1 terabyte, making it difficult to find an online repository. Readers should contact the first author for data access.

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