Abstract
Previous work indicates that increasing Arctic temperatures are leading to permafrost degradation and increased numbers of thermokarst features. Our goal was to use ground‐penetrating radar (GPR) to investigate depth‐to‐permafrost in areas with developing thermokarst features and to study how surface expression (ex: slope failure, thaw depressions) and the permafrost table are related. We also conducted a model study to investigate the potential for monitoring subsurface flow with GPR and electrical resistivity. We investigated sites in arctic Alaska with a range of surface morphologies. Using 250 MHz antennas, we conducted 3‐D GPR surveys over three features: a large thermokarst failure, a thaw slump, and an area of poorly developed patterned ground. We also conducted 2‐D GPR surveys at two adjacent small drainages: one in which thermokarst features and slope failure were evident, and one in which anomalous surface features were absent. We found depth‐to‐permafrost was often greatest in the vicinity of slump or slope failures. In some cases, well‐developed linear thaw depressions were evident along the thaw table, though there was no surface expression. This suggests the possibility of preferential flow within the subsurface, which could substantially alter the permafrost before surface features become evident. We created a simplified model of groundwater flow based on our field observations. To determine the best method for detecting subsurface flow, we simulated salt tracer tests coupled with time‐lapse electrical resistivity surveys over the thaw anomaly, using a variety of electrode configurations, GPR antenna frequencies, different concentrations of tracer, and different levels of saturation. We found that combined dipole‐dipole and Wenner arrays were suitable for monitoring tracer movement through a small (10 cm depth) thaw table melt channel.
Published Version
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