Transient Hillslope Responses to Permafrost Loss
Abstract
The rapid and catastrophic erosion of soil on hillslopes underlain by permafrost has been attributed to rapid deepening of seasonally thawed surface material and the loss of near-surface permafrost. These erosional events both redistribute sediment, reshape hillslopes, and have the potential to release soil carbon from previously stable sinks. At a series of small watersheds on the southern Seward Peninsula in Alaska, we have documented a range of soil movement processes affected by the presence and loss of permafrost. These movements range from steady creep-like behavior to rapid and repetitive failures. Based on direct field observations and geophysical imaging of the subsurface, we have mapped the presence and absence of near surface permafrost across these watersheds. A comparison of the permafrost map to the spatial patterns of annual ground surface displacement and failures suggests that regions of recent and/or active permafrost loss exhibit the greatest rates of movement. Despite topographic evidence of past failures, regions without permafrost have the lowest rates of present-day movement. Regions of relatively stable and continuous permafrost appear to have intermediate rates of soil creep and lack catastrophic erosional features. Our observations suggest that the greatest hillslope instability occurs in the transitional regions undergoing rapid permafrost loss. Both the rates and extent of propagation of failures into the surrounding landscapes appears to be influenced by the connectivity of failures to the network of established channels and developing gullies. If our small watersheds are representative of larger swathes of permafrost landscapes, then we expect to see an acceleration of hillslope processes during and immediately following permafrost loss followed by a reduction in soil transport rates and a stabilization of the landscape.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMEP42A..52R