Revealing the Internal Structure of the Rock Glacier - Debris Covered Glacier Continuum from Drone-Based Ground-Penetrating Radar

Rock glaciers (RGs) and Debris-Covered Glaciers (DCGs) are end-members of a continuum of ice-rich landforms found in alpine and polar environments. Although often considered more resilient to climate warming than debris-free glaciers, recent studies have shown that RG-DCGs also exhibit accelerated movement and degradation under warming conditions. Understanding these responses requires surface monitoring and subsurface characterization, the latter commonly achieved with ground-penetrating radar (GPR), a geophysical method capable of revealing the internal stratigraphy of these glaciers. In particular, GPR allows us to quantify the supraglacial debris thickness, total landform thickness, ice purity, and the presence of englacial stratigraphy. However, traditional surface-based GPR can be time-consuming and often hazardous, requiring manual traversal across rough, steep, and icy terrain—some of which may be inaccessible. To overcome these limitations, we integrated a drone-based GPR (DGPR) that consists of a MALA Geodrone 80 GPR mounted on a DJI Matrice 600 Pro, with a UgCS SkyHub system for automated terrain following. We tested our system at two ice-cored RGs: Sourdough, Alaska, and Galena Creek, Wyoming. At both sites, we compare the 80 MHz DGPR with a surface-based GPR pulseEKKO system at different center frequencies (50 MHz, 100 MHz, and 200 MHz), providing a range of vertical resolutions. We validated the internal reflectors with clutter simulations to discriminate genuine subsurface reflectors from off-nadir surface reflections (see figure below). DGPR resolved a maximum bulk glacier thickness of 28.5 m at Sourdough and 48.6 m at Galena Creek. Mean supraglacial debris thickness in Sourdough was 1.5 m, At Galena Creek, we found a mean debris thickness of 0.8 m in extensional sections and 1.4 m in compressional sections, which result from glacial flow stress-strain spatial patterns. We also detected internal debris layers outcropping at the cirque of Galena Creek. We estimated ages of ice and debris deposition by combining the outcrop locations with surface velocity data. We demonstrated that DGPR provides a safe and efficient method that enables more extensive and denser surveys than traditional GPR, improving the characterization of RG-DCGs as dynamic components of the cryosphere.