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Calving and submarine melt drive frontal ablation and sculpt the ice face of marine-terminating glaciers. However, there are sparse observations of submarine termini, which limit estimates of spatially varying submarine melt. Here we present a detailed survey of a west Greenland glacier to reveal heterogeneity in submarine terminus morphology. We find that the majority of the terminus (similar to 77%) is undercut, driven by calving in the upper water column and submarine melting at depth. The remaining similar to 23% of the terminus is overcut, driven by calving alone. We use observations of six subglacial discharge outlets, combined with a plume model, to estimate spatially varying discharge fluxes. While small discharge fluxes (<43 m(3)/s) feed numerous, deeply undercut outlets with subsurface plumes, similar to 70% of the net subglacial flux emerges at the terminus center, producing a vigorous, surface-reaching plume. This primary outlet drives large, localized seasonal retreat that exceeds calving rates at secondary outlets.

Plain Language Summary Using a sensor to map the shape of a glacier terminus below sea level, we are able to quantify how the terminus shape changes across the glacier. This allows us to identify different classes of terminus shape, which vary from undercut to overcut. Undercut regions are formed through melting focused near the base of the terminus, where freshwater emerges from discrete channels. Using a model, we explain the degree of undercutting found in channels by varying the flux of freshwater emerging from each channel. This allows us to understand the relative role of small channels on total terminus melt compared to much larger, more frequently observed channels. We find that small channels produce significant melting compared to a much larger channel at the glacier center but not as much iceberg calving.