Application of 3D electrical resistivity imaging for mapping frozen ground conditions exemplified by three case studies

Periglacial landscapes comprise landforms that are inherently 3D structures, often exhibiting small-scale spatial heterogeneity of surface and subsurface conditions. The objectives of the present paper are to illustrate the potential of the novel application of 3D electrical resistivity imaging for mapping frozen ground conditions exemplified by three case studies with different geomorphological problems to be addressed and to consider the efficacy of the 3D approach to geomorphological investigations in mid-latitude high alpine and high latitude lowland permafrost environments.The approach described in the three case studies includes reconnaissance surveys using two-dimensional electrical resistivity tomography (2D ERT) followed by a detailed mapping using three-dimensional electrical resistivity imaging (3D ERI). The latter approach enables a spatial imaging of the subsurface resistivity distribution and clearly improves the delineation and characterization of subsurface structures compared to state-of-the-art 2D ERT that is limited to findings gained along single profiles or extrapolation between several profiles. Although it can be challenging and time-consuming to apply this technique in periglacial environments, the promising results demonstrate its value for the 3D delineation of frozen ground conditions. In the case of the described case study sites, characterizing the subsurface heterogeneity is close to impossible using drilling or 2D geophysical surveying alone because of the complex 3D nature of the frozen ground characteristics comprising permafrost and permafrost-free areas (alpine permafrost test site) as well as permafrost with variable characteristics (subarctic lowland permafrost test site) at close distance. Even in environments that seem homogeneous at first sight, this method allows us to detect substantial subsurface property variations that can be attributed to different frozen ground conditions. Furthermore, 3D ERI allows the linking of different data sources (e.g., site-specific geomorphology and hydrology) to enhance the spatial understanding of surface and subsurface characteristics and dynamics in permafrost environments. The improved knowledge of the geophysical anatomy and subsurface architecture of the permafrost occurrences revealed by this study suggests a more widespread use for glacial and periglacial landform studies in the future.