Evidences of Bedrock Forcing on Glacier Morphodynamics: A Case Study in Italian Alps

In mountain glaciers, the influence of bedrock geometry on glacier surface morphology isoften assumed; quantitative evidence, however, is rare. In our research, we measured theice thickness of the Planpincieux Glacier (North-west Italy) and detected the bedrocktopography using ground-penetrating radar. Additionally, we investigated the glaciersurface morphology using structure from motion and the glacier kinematics usingdigital image correlation of terrestrial images. A digital terrain analysis showed evidenceof recurrent crevasses whose position corresponded to bedrock steps. On average, since2014, their positions varied between 6 and 14m and were 40 ± 8m downstream of thebedrock steps. Bedrock and glacier topography presented out-of-phase correlatedundulations that approximately fit a sinusoidal function of different amplitude.Moreover, we show the morphological evolution of an unstable sector whosethickness at the end of the ablation seasons has remained approximately constantsince 2014. Contrarily, the ice melting during the 2020 ablation season caused avolume loss of >30%. Since, in general, the damages provoked by a potential iceavalanche depend primarily on the involved volume, this finding demonstrates thatfrequent morphology monitoring is essential for correct glacial hazard assessment.