Almost half of the Greenland ice sheet's mass loss occurs through iceberg calving at marine terminating glaciers. The presence of buoyant subglacial discharge plumes at these marine termini are thought to increase mass loss both through submarine melting and by undercutting that consequently increases calving rates. Plume models are used to predict submarine melting and undercutting. However, there are few observations that allow these relationships to be tested. Here, we use airborne lidar from the terminus of Helheim Glacier, SE Greenland to measure the bulge induced at the surface by the upwelling plume. We use these measurements to estimate plume discharge rates using a high‐resolution, three‐dimensional plume model. Multiyear observations of the plume are compared to a record of calving from camera and icequake data. We find no evidence to suggest that the presence of a plume, determined by its visibility at the surface, increases the frequency of major calving events and also show that mass loss at the terminus driven directly by plume discharge is significantly less than mass loss from major calving events. The results suggest that the contribution of direct plume‐driven mass loss at deep marine‐terminating glaciers may be less than at shallower termini.
Many large calving events at Greenland's marine‐terminating glaciers generate globally detectable glacial earthquakes. We perform a cross‐correlation analysis using regional seismic data to identify events below the teleseismic detection threshold, focusing on the 24 hr surrounding known glacial earthquakes at Greenland's three largest glaciers. We detect additional seismic events in the minutes prior to more than half of the glacial earthquakes we study and following one third of them. Waveform modeling shows source mechanisms like those of previously known glacial earthquakes, a result consistent with available imagery. The seismic events thus do not represent a failure of the high subaerial ice cliff like that expected to trigger large‐scale calving and a marine ice‐cliff instability but, rather, rotational, buoyancy‐driven calving events, likely of the full glacier thickness. A limited investigation of the prevalence of smaller seismic events at times outside glacial‐earthquake windows identifies several additional events. However, we find that calving at the three glaciers we study—Jakobshavn Isbræ, Helheim Glacier, and Kangerdlugssuaq Glacier—often occurs as sequences of discrete buoyancy‐driven events in which multiple icebergs ranging in size over as much as three orders of magnitude are all lost within ∼30 min. We demonstrate a correlation between glacial‐earthquake magnitude and iceberg size for events with well‐constrained iceberg‐area estimates. Our results suggest that at least 10–30% more dynamic mass loss occurs through buoyancy‐driven calving at Greenland's glaciers than previously appreciated.
more » « less- PAR ID:
- 10461077
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 124
- Issue:
- 7
- ISSN:
- 2169-9003
- Format(s):
- Medium: X Size: p. 1899-1918
- Size(s):
- p. 1899-1918
- Sponsoring Org:
- National Science Foundation
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