Geophysical analysis of transverse ridges and internal structure at Lone Peak Rock Glacier, Big Sky, Montana, USA

Abstract

Rock glaciers are periglacial alpine landforms that are found in many locations worldwide. Whereas well-developed models of deformation are established for traditional alpine glaciers, rock glacier deformation is poorly understood. Geophysical data from Lone Peak Rock Glacier (LPRG), southwest Montana, USA, are paired with lidar bare-earth 1m digital elevation model (DEM) analysis to explore potential genetic relationships between internal composition, structure and regularly spaced arcuate transverse ridges expressed at the rock glacier surface. The internal composition of LPRG is heterogeneous, with frozen debris and clean ice overlain by an unconsolidated talus mantle. Upslopedipping, clearly distinguished reflectors in the ground-penetrating radar (GPR) longitudinal survey at LPRG correspond to transverse ridges. The spacing and slope of individual features at the surface and in the subsurface were measured and compared and are found to be similar. The structures observed at LPRG and other rock glaciers are similar to structures detected in glaciotectonically altered sediment, ice-cored moraines and other rock glacier settings. This finding suggests that transverse ridges on rock glaciers may be used as geomorphic indicators of internal deformation. This study contributes to the body of research on the application of GPR to rock glaciers, and is the first to directly pair and analyze individual surface topographic features with internal structures.