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Abstract Debris‐covered glaciers (DCG) and rock glaciers have been increasingly studied in recent years because of the role they play within local watersheds, glacial ablation models due to climate change, and as analogs for buried ice features on planetary bodies such as Mars. Characterizing the supraglacial debris layer is a large part of these efforts. Geophysical exploration of DCG has mostly excluded active seismic methods, with the exception of refraction studies, due to the attenuating properties of the debris cover and field survey efficiency. We evaluate the accuracy, field efficiency, and effectiveness of seismic refraction, reflection, and surface‐wave surveys for determining the elastic properties of the debris layer and any underlying layers on DCG using the Sourdough Rock Glacier in Southcentral Alaska as a test site. We provide evidence for imaging an ultra‐shallow seismic reflection from the bottom of the loose debris layer using ultra‐dense receiver arrays and compare it to ground‐penetrating radar (GPR) images taken along the same profiles. We also detail how reliable dispersion curve images can be extracted from the surface wave package of the seismic data using the multi‐channel analysis of surface waves technique, which allows for the (s)‐wave profile to be inverted for. We find this could be a valuable addition to the toolbox of future geophysical investigations on DCG. 

Abstract Malaspina Glacier, located on the coast of southern Alaska, is the world's largest piedmont glacier. A narrow ice‐cored foreland zone undergoing rapid thermokarst erosion separates the glacier from the relatively warm waters of the Gulf of Alaska. Glacier‐wide thinning rates for Malaspina are greater than 1 m/yr, and previous geophysical investigations indicated that bed elevation exceeds 300 m below sea level in some places. These observations together give rise to the question of glacial stability. To address this question, glacier evolution models are dependent upon detailed observations of Malaspina's subglacial topography. Here, we map 2,000 line‐km of the glacier's bed using airborne radar sounding data collected by NASA's Operation IceBridge. When compared to gridded radar measurements, we find that glaciological models overestimate Malaspina's volume by more than 30%. While we report a mean bed elevation 100 m greater than previous models, we find that Malaspina inhabits a broad basin largely grounded below sea level. Several subglacial channels dissect the glacier's bed: the most prominent of these channels extends at least 35 km up‐glacier from the terminus toward the throat of Seward Glacier. Provided continued foreland erosion, an ice‐ocean connection may promote rapid retreat along these overdeepened subglacial channels, with a global sea‐level rise potential of 1.4 mm.