Calving Mechanisms Inferred From Observations of Surface Depressions at Helheim Glacier, Greenland

Dynamical changes at the termini of tidewater glaciers may trigger sustained acceleration, thinning, and retreat, increasing a glacier's contribution to sea level rise. However, processes at the ice-ocean interface occur across a range of spatial (cm to km) and temporal (minutes to years) scales, making these processes difficult to capture with many existing observational strategies. To fill this observational gap, we installed two autonomous terrestrial laser scanners overlooking the terminus at Helheim Glacier, East Greenland, the first in 2015 and the second in 2018. Each laser scanner system scans every six hours during non-winter months and once a day during winter; together, these systems generate an extraordinary amount of data, including georeferenced point clouds, digital elevation models, velocity, and strain rates of Helheim Glacier. Our results show that large surface depressions form at a near-consistent location on the lee side of a subglacial ridge and have increased in occurrence over time. We also present the first inferences of Helheim Glacier's grounding zone location and observed over 3 km of grounding zone retreat between 2018–2019. Furthermore, we identify and catalog calving events that we compare with our velocity products. We find that Helheim Glacier does not undergo sustained acceleration after individual calving episodes, and variations in calving style do not impact velocity responses. Our work reveals the insensitivity of Helheim Glacier to iceberg calving during our observational record and the importance of high temporal resolution data in inferring grounding zone dynamics.