Electrical Resistivity Tomography for the 2D and 3D Investigation of Pingos and Permafrost Mounds in Northern Canada's Mountain and Coastland Areas

ABSTRACT Pingos and related permafrost mounds are widespread periglacial landforms in Arctic environments that are ice‐rich on the one hand and contain taliks on the other, making them vulnerable to climate change. So far, the interior, geophysical characteristics, and distribution of ground ice within these dome‐ or cone‐shaped features have not been sufficiently investigated, and more in situ observations and multidimensional insights are required. This study presents two‐ and three‐dimensional Electrical Resistivity Tomography (ERT) results from numerous pingos and permafrost mounds investigated in the Ogilvie Mountains and on the Tuktoyaktuk Peninsula, northwest Canada. The measurements cover single features and assemblages of varying sizes and shapes, in mountain valleys, on slopes and at riversides, in drained lakes, and at lakeshores. Resistivities are compared based on representative zones of interest within 2D profiles, and large quasi‐3D grids were set up to test the capabilities of 2D ERT and especially 3D ERT for the investigation of pingos and permafrost mounds. Using this data, the study helps to decipher the origin and development of the landforms, exemplified for specific sites in mountainous vs. coastal environments by additionally considering their complex hydrological settings. The pingos reveal median interior electrical resistivities of 5–50 kΩm, and all have maximum resistivities exceeding 10 kΩm. The bigger ones feature cores of far beyond 100 kΩm, which contrasts with the often more conductive interiors of smaller or different types of permafrost mounds. Difficulties arise when deriving a common resistivity threshold for massive pingo ice. ERT is a powerful tool to three‐dimensionally display the interior of pingos, to detect potential talik areas, and to help to distinguish pingos from other mound landforms based on geoelectrical properties. It enables the estimation of the upper limit and the lateral extent of massive ice cores, but in many cases struggles to provide reliable information on structures below massive ice. Investigating pingos using ERT, therefore, requires careful evaluation of the model sensitivity. The ERT findings and hydrological discussion underline the probable co‐existence of hydraulic and hydrostatic pingos in mountain valleys, and reveal similar characteristics and positions of permafrost mounds as of open‐system pingos. However, the position, lateral extent, and electrical properties of internal massive ice vary between sites and even within single assemblages. Specifically, within the biggest investigated pingo on the Tuktoyaktuk Peninsula, the extent of the detected ice core hardly explains the size and surface appearance of the landform, whereas conductive, likely unfrozen or solute‐rich pockets in the flanks cause an even more heterogeneous internal structure. The investigated examples paint a much more complex picture of the pingo architecture and genesis than traditional models have suggested to date.