Identifying ice-rich layers in rock glaciers using geophysics: A case study in the Andes

Abstract

Rock glaciers play an important hydrological role in the semi-arid Andes, by providing water to streamflow when water needs are the most. Identifying if a rock glacier contains more or less ice is not an easy task, because most of the time, the ice is buried below rock blocks. Surface based geophysics can be a way to assess ice content, even tough calibration or ground truth is necessary to properly give any quantitative figure. This study aims to identify ice rich layers using geophysics on two Rock Glaciers (RG): an active and inactive one. Electrical Resistivity Tomography (ERT), Seismic Refraction Tomography (SRT) and Ground Penetrating Radar (GPR) surveys were carried out on those two RG. Seismic velocities and resistivity are higher in the active RG, which is in agreement with a higher ice content. Whilst velocities are in still in the usual geological range, resistivities are really high, which is not abnormal in the absence of liquid water or clay minerals. Interpretating resistivities only could led to misunderstandings because high resistivities could be seen as ice. The two RGs show a distinct signature regarding seismic velocities and resistivities, which demonstrate the potential of those tools to characterize RG.