Observing rock moisture changes using electrical resistivity tomography in frost weathering caves

Abstract

Frost weathering has been identified as a factor contributing to the formation of caves in alpine and cold regions. Rock moisture has been determined to be the critical factor for effective frost weathering. In solid rock formations, fissures and fractures are of significance in water migration and heat flow between the atmosphere and the rock. These features can also be indicative of zones of weakness within the rock mass. Fissures and fractures are thus a prerequisite for frost weathering. The present study employs electrical resistivity tomography (ERT) to investigate the presence of fractures that act as preferential flow paths, and to determine temporal and spatial changes in rock moisture in three caves in Lower Austria. These caves are likely shaped by frost weathering. Measurements were taken on four to six occasions over a period of 25 months, using two ERT profiles per cave. The first profile utilised 45 cm electrode spacing with the objective of capturing large-scale moisture distribution. The second profile employed 11 cm electrode spacing (high resolution) to resolve fractures and water pathways. Parameters such as rock temperature, precipitation, and radiation were measured on-site to evaluate the interpretation of the ERT results. Normalised difference plots of the time-lapse analysis revealed moisture fluctuations attributable to external factors, including precipitation and temperature. Our results reveal the potential of ERT for understanding rock moisture dynamics in frost weathering contexts and call for further investigation with higher temporal resolution to elucidate weathering processes.