| Abstrakt: |
The Arctic is experiencing rapid climate change, and the effect on hydrologic processes and resulting geomorphic changes to hillslopes and channels is unclear because we lack quantitative models and theory for rapid changes resulting from thawing permafrost. The presence of permafrost modulates water flow and the stability of soil‐mantled slopes, implying that there should be a signature of permafrost processes, including warming‐driven disturbance, in channel network extent. To inform understanding of hillslope‐channel dynamics under changing climates, we examined soil‐mantled hillslopes within a ∼300 km2 area of the Seward Peninsula, western Alaska, where discontinuous permafrost is particularly susceptible to thaw and rapid landscape change. In this study, we pair high‐resolution topographic and satellite data to multi‐annual observations of InSAR‐derived surface displacement over a 5‐year period to quantify spatial variations in topographic change across an upland landscape. We find that neither the basin slope nor the presence of knickzones controls the magnitude of recent surface displacements within the study basin, as may be expected under conceptual models of temperate hillslope evolution. Rather, the highest displacement magnitudes tended to occur at the broad hillslope‐channel transition zone. In this study area, this zone is occupied by water tracks, which are zero‐order ecogeomorphic features that concentrate surface and subsurface flow paths. Our results suggest that water tracks, which appear to occupy hillslope positions between saturation and incision thresholds, are vulnerable to warming‐induced subsidence and incision. We hypothesize that gullying within water tracks will outpace infilling by hillslope processes, resulting in the growth of the channel network under future warming. Plain Language Summary: Climate and ecology can shape hillslopes and the extent of river networks by controlling how much water is available for erosion. These forces also control whether water can erode soil if it is strengthened by ice or roots. The permeability and stability of permafrost hillslopes change with seasonal and long‐term warming due to frozen ground's impermeability and resistance to erosion. This link between temperature and erosion in permafrost landscapes is thus more direct than most geomorphic models developed at lower latitudes presume. We related the locations of satellite topographic change to the geomorphic processes that dominate that part of the landscape based on the shape of the hillslopes and valleys. This allows us to determine whether the pattern of disturbance across the landscape is related to geomorphic variables such as slope or climate‐modulated variables such as soil saturation. Topographic change primarily occurs in saturated areas at the tips of the river network. At these locations, features called "water tracks" form the transition between hillslopes and river valleys. Changes in climate and vegetation in permafrost landscapes are potentially driving water tracks to transition into true channels, expanding the channel network. Key Points: Seasonal and long‐term permafrost thaw change hillslope hydrology and erodibilitySatellites observe surface displacements concentrated at the transition between hillslopes and channelsA conceptual model is proposed for hillslope‐channel transitions in permafrost landscapes mediated by water tracks [ABSTRACT FROM AUTHOR] |
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