Active Layer Variability and Permafrost Stability on Axel Heiberg Island: Comparing Electrical Resistivity Tomography and Ground-Penetrating Radar

High Arctic landscapes are undergoing rapid change, warming at least four times faster than the global average. Because these regions are dominated by continuous permafrost, thawing leads to deeper active layers (AL) and increasing groundwater infiltration, altering hydrology and mobilizing nutrients and metals. This study was designed to compare the effectiveness of electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) for characterizing permafrost environments and capturing short-term thaw dynamics. Fieldwork took place on a west-facing slope at Expedition Fiord, Axel Heiberg Island, where two 20 m transects (NShill and WEhill) were surveyed repeatedly over five days (July 23–27, 2025). Surveys used ERT (Wenner and dipole-dipole arrays), GPR (500 MHz), permafrost probing, and soil probes (moisture, temperature, conductivity). The original aim was to evaluate how the two geophysical methods compare, while testing the hypothesis that AL properties respond strongly to weather variability, whereas permafrost (PF) remains relatively stable. Results confirm that the AL is highly sensitive to both weather and microtopography, while PF resistivity remained stable within orders of magnitude over the study period. Soil data showed persistent wet anomalies at NShill (electrodes 10–12), while WEhill responded more directly to rainfall and drying. ERT consistently resolved a conductive AL above resistive PF, with saturation beneath puddles producing reduced resistivity and stronger attenuation. GPR showed a strong reflective band at ~3–7 ns (AL boundary) and signal loss below ~10–12 ns, especially at saturated troughs. Across methods, AL thickness followed the relation probe ≤ GPR ≤ ERT, reflecting that each technique senses different physical boundaries. Together, the datasets demonstrate that ERT and GPR are complementary tools: ERT resolves the boundary between active layer and permafrost, while GPR highlights finer-scale thaw patterns and moisture variability near the surface.