Seismic and GPR surveys of Mullins Glacier, McMurdo Dry Valleys, Antarctica: ice thickness, internal structure and implications for surface ridge formation

We present results from ground-penetrating radar (GPR) and seismic surveys for the Mullins Valley debris-covered glacier (Mullins Glacier), Antarctica, that yield local ice-thickness estimates of 80-110 m in upper Mullins Valley and 150 m in upper Beacon Valley. Englacial debris in upper Mullins Glacier occurs as scattered cobbles and as discrete layers. One extensive englacial debris layer, which appears as a coherent reflector dipping 40-45 degrees up-valley, intersects the ground surface within an similar to 8m high ice-cored ridge, the largest of several ridges that mark the glacier surface. Field excavations reveal that this englacial interface consists of multiple debris bands that can be directly correlated with ridge microtopography. Englacial debris layers most probably originate as concentrated rockfall in ice accumulation zones and/or as surface lags that form as dirty ice sublimes during periods of negative mass balance. A similar pattern of surface ridges on Friedman Glacier (similar to 2.5 km west of Mullins Glacier) suggests regional environmental changes are involved in ridge formation. These observations carry implications for evaluating debris entrainment and surface ridge formation mechanisms in cold-based, debris-covered glaciers and provide a glaciological framework for evaluating and interpreting paleoclimate records from Mullins Glacier.