Geophysical and kinematic investigation of low-altitude rock glaciers on Mount Mestas, southern Colorado

Abstract

This study presents a multi-method investigation of two rock glaciers within the low-altitude periglacial environment of Mount Mestas in southern Colorado, a region generally underrepresented in rock glacier research. Electrical resistivity tomography (ERT), satellite radar interferometry (InSAR), and historical aerial photogrammetry were combined to characterize the subsurface structure, ice distribution, and surface kinematics of both features. Four ERT profiles on RG South resolved a spatially heterogeneous permafrost body beginning at approximately 8 m depth, with an estimated volume of ~485,500 m³ and resistivity values consistent with ice-rich permafrost; a secondary permafrost body associated with a superimposed lobe was also identified. InSAR analysis revealed that surface displacement on RG South is spatially concentrated where the permafrost body is laterally continuous, rather than where it is thickest, suggesting that permafrost geometry instead of ice volume is the primary control on surface displacement at this site. On RG North, displacement rates of 2–12 cm/yr were recorded, consistent with the 7.9 cm/yr average annual rate derived from 1938–2019 photogrammetric analysis of tree displacement, with no evidence that the 1963 anthropogenic toe excavation measurably altered the feature's kinematics. Taken together, the results indicate that both rock glaciers are in a state of long-term decline driven primarily by post-glacial permafrost degradation, with active deformation increasingly restricted to remnant core ice bodies while peripheral lobes become thermally and kinematically inactive which is a trajectory consistent Holocene warming in the Southern Rocky Mountains.