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.
Submarine melting and iceberg calving are two important processes that control mass loss from the terminus of tidewater glaciers. There have been significant efforts to quantify the effect of submarine melting on glacier calving, but controversy remains with conflicting studies indicating submarine melting can increase, decrease, or has minimal effect on calving. Here we show using a two‐dimensional full Stokes finite element model that submarine melt can alter the state of stress near the terminus and the changes in stress exert a first‐order control on the calving regime of marine terminating glaciers. The model calculates both the largest principal and maximum shear stresses and then maps out where tensile and shear failure occur for a range of melt rates and vertical melt profiles. We find that submarine melt initially promotes full thickness calving events. However, as the melt rate further increases, an overhang begins to form and resulting compressive stresses suppress full thickness calving. These results are relatively insensitive to basal friction. Moreover, our results suggest that submarine melting can both increase and decrease calving rates with the magnitude and sign of the effect determined by the shape of the melt profile and the relative magnitude of average melt rate. Despite the fact that calving is suppressed in some circumstances, the addition of submarine melt almost always increases the total mass loss. Overall, we find that relatively small amounts of submarine melt can destabilize glaciers, but calving and frontal ablation are increasingly controlled by submarine melt as it continues to increase.
more » « less- PAR ID:
- 10459619
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 124
- Issue:
- 2
- ISSN:
- 2169-9003
- Page Range / eLocation ID:
- p. 334-346
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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