ИСТИНА

Electrotomography and resistivity measurements are modern visualisation methods, applicable for non-destructive underground surveys. This method is based on differences in resistivity of frozen and thawed soil, fresh and saline water, ice and mineral phases. In permafrost regions it can be applied to understand heterogeneity in the active layer and to search for ice-rich bodies. These factors are strongly connected with permafrost thaw and related processes. By using a large number of electrodes we can obtain pseudo cross-sections, where top layers of data points contain resistivity, measured from neighbor electrodes and bottom layers -- from electrodes with higher distances between each other. Obtained cross-section can be compared with another methods of probing, like acoustic methods and permafrost coring. We conducted resistivity surveys of continuous permafrost in Kolyma River basin in Northeastern Siberia. Measurements were made at several sites, including experimentally burned plots, near permafrost coring sites and at yedoma deposits exposure at Dyvanny Yar cliff. We changed the spacing between electrodes to measure resistivity from different depths. For measurements of active layer depth (~ 0.5-1.5m) we used 0.3-0.5m spacing and compared obtained results with direct probing of thaw layer. We found a relationship between measured and real depth. For deeper surveys (up to 10m depth) we used larger spacing -- 2-3m between electrodes. Comparison of resistivity cross-sections with permafrost core data and visual observation at Dyvanny Yar show possibility of finding ice wedge positions and agreement between average resistivity of bottom layers and ice content in the permafrost at a similar depth. Resistivity measurements in continuous permafrost are challenging but our results suggest that the method could be useful for examination of thawing changes.