Calving Mechanisms Inferred from Observations of Surface Depressions at
Helheim Glacier, Greenland
Abstract
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. 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 6 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 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; we observed over 3 km of grounding zone retreat and slightly
over 1 km of grounding line migration within a tidal cycle 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.