Arctic rockwall retreat rates estimated using laboratory-calibrated ERT measurements of talus cones in Longyeardalen, Svalbard

摘要

Holocene rockwall retreat rates quantify integral values of rock slope erosion and talus cone evolution. Here we investigate Holocene rockwall retreat of exposed arctic sandstone cliffs in Longyeardalen, central Svalbard and apply laboratory-calibrated electrical resistivity tomography (ERT) to determine talus sediment thickness. Temperature-resistivity functions of two sandstone samples are measured in the laboratory and compared with borehole temperatures from the talus slope. The resistivity of the higher and lower-porosity sandstone at relevant borehole permafrost temperatures defines a threshold range that accounts for the lithological variability of the dominant bedrock and debris material. This helps to estimate the depth of the transition from higher resistivities of ice-rich debris to lower resistivities of frozen bedrock in the six ERT transects. The depth of the debris-bedrock transition in ERT profiles is confirmed by a pronounced apparent resistivity gradient in the raw data plotted versus depth of investigation. High-resolution LiDAR-scanning and ERT subsurface information were collated in a GIS to interpolate the bedrock surface and to calculate the sediment volume of the talus cones. The resulting volumes were referenced to source areas to calculate rockwall retreat rates. The rock mass strength was estimated for the source areas. The integral rockwall retreat rates range from 0.33 to 1.96mmyr -1, and are among the highest rockwall retreat rates measured in arctic environments, presumably modulated by harsh environmental forcing on a porous sandstone rock cliff with a comparatively low rock mass strength. Here, we show the potential of laboratory-calibrated ERT to provide accurate estimates of rockwall retreat rates even in ice-rich permafrost talus slopes.