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Abstract Post‐seismic debris flows are an important hazard following large earthquakes, propagating destruction downstream from hillslopes where coseismic landslides occur and extending damage for years after shaking stops. Data sets of post‐seismic debris flows are necessary to predict initiation and runout characteristics but are presently scarce. We used satellite imagery supplemented by field observations to compile an inventory of >1,000 debris flows associated with the 2015 Gorkha Earthquake in Nepal. We identified two distinct debris flow types: (1) Material from a coseismic landslide was remobilized in a steep channel during a later monsoon; and (2) a new post‐seismic hillslope failure occurred in saturated conditions and became fluidized and channelized. Runout distance was constrained by channel confluences and may be related to confluence geometry. Unstable landslide debris was largely flushed from steep channels during the first monsoon following the earthquake, and the rate of new hillslope failures tailed off over a few years.
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Post-fire evolution of ravel transport regimes in the Diablo Range, CA
Abstract. Post-fire changes to the transport regime of dry ravel, which describes the gravity-driven transport of individual particles downslope, are poorly constrained but critical to understand as ravel may contribute to elevated sediment fluxes and associated debris flow activity observed post-fire in the western United States. In this study, we evaluated post-fire variability in dry ravel travel distance exceedance probabilities and disentrainment rates in the Diablo Range of central coastal California following the Santa Clara Unit Lightning Complex fire of August 2020. Between March 2021 and March 2022, we conducted repeat field experiments simulating ravel with in situ particles (3–35 mm diameter) on a range of experimental surface gradients (0.38–0.81) on both grassy south-facing slopes and oak woodland north-facing slopes. We characterized post-fire evolution in particle transport by fitting a probabilistic Lomax distribution model to the empirical travel distance exceedance probabilities for each experimental particle size, surface gradient, and time period. The resulting Lomax shape and scale parameters were used to identify the transport regime for each subset of simulated ravel, ranging from “bounded” (light-tailed or local) to “runaway” (heavy-tailed or nonlocal) motion. Our experimental results indicated that as vegetation recovered over the first 2 years post-fire, the behavior of small particles (median intermediate axis of 6 mm) became less similar across the experimental sites due to different vegetation structures, whereas medium and large particles (median intermediate axes of 13 and 28 mm, respectively) exhibited a general transition from more runaway to more bounded transport, and large particles became less sensitive to surface gradient. All particle sizes exhibited a decrease in the length scale of transport with time. Of all particle subsets, larger particles on steeper slopes were more likely to experience nonlocal transport, consistent with previous observations and theory. These findings are further corroborated by hillslope and channel deposits, which suggest that large particles were preferentially evacuated from the hillslope to the channel during or immediately after the fire. Our results indicate that nonlocal transport of in situ particles likely occurs in the experimental study catchment, and the presence of wildfire increases the likelihood of nonlocal transport, particularly on steeper slopes.
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- Award ID(s):
- 2123220
- PAR ID:
- 10580851
- Publisher / Repository:
- EGU
- Date Published:
- Journal Name:
- Earth Surface Dynamics
- Volume:
- 12
- Issue:
- 6
- ISSN:
- 2196-632X
- Page Range / eLocation ID:
- 1415 to 1446
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/esurf-12-1415-2024
