Submarine melt can account for substantial mass loss at tidewater glacier termini. However, the processes controlling submarine melt are poorly understood due to limited observations of submarine termini. Here at a tidewater glacier in central West Greenland, we identify subglacial discharge outlets and infer submarine melt across the terminus using direct observations of the submarine terminus face. We find extensive melting associated with small discharge outlets. While the majority of discharge is routed to a single, large channel, outlets not fed by large tributaries drive submarine melt rates in excess of 3.0 m d−1 and account for 85% of total estimated melt across the terminus. Nearly the entire terminus is undercut, which may intersect surface crevasses and promote calving. Severe undercutting constricts buoyant outflow plumes and may amplify melt. The observed morphology and melt distribution motivate more realistic treatments of terminus shape and subglacial discharge in submarine melt models.

Ice loss from the world’s glaciers and ice sheets contributes to sea level rise, influences ocean circulation, and affects ecosystem productivity. Ongoing changes in glaciers and ice sheets are driven by submarine melting and iceberg calving from tidewater glacier margins. However, predictions of glacier change largely rest on unconstrained theory for submarine melting. Here, we use repeat multibeam sonar surveys to image a subsurface tidewater glacier face and document a time-variable, three-dimensional geometry linked to melting and calving patterns. Submarine melt rates are high across the entire ice face over both seasons surveyed and increase from spring to summer. The observed melt rates are up to two orders of magnitude greater than predicted by theory, challenging current simulations of ice loss from tidewater glaciers.

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Marine‐terminating glaciers play a critical role in controlling Greenland's ice sheet mass balance. Their frontal margins interact vigorously with the ocean, but our understanding of this interaction is limited, in part, by a lack of bathymetry data. Here we present a multibeam echo sounding survey of 14 glacial fjords in the Uummannaq and Vaigat fjords, west Greenland, which extends from the continental shelf to the glacier fronts. The data reveal valleys with shallow sills, overdeepenings (>1300 m) from glacial erosion, and seafloor depths 100–1000 m deeper than in existing charts. Where fjords are deep enough, we detect the pervasive presence of warm, salty Atlantic Water (AW) (>2.5°C) with high melt potential, but we also find numerous glaciers grounded on shallow (<200 m) sills, standing in cold (<1°C) waters in otherwise deep fjords, i.e., with reduced melt potential. Bathymetric observations extending to the glacier fronts are critical to understand the glacier evolution.

We have investigated the impact of Hurricane Ike on the shoreface of the Bolivar Peninsula, Texas, using three near-surface marine geophysical surveys during a five-year span following the storm, which made landfall in September of 2008. Multibeam bathymetry, sidescan backscatter, and CHIRP subbottom reflection data were collected during each survey. The first survey, in November, 2008, discovered the presence of an erosional, landward-facing scarp across a broad of the barrier spit shoreface at approximately 3.5-m water depth. The erosion incised into a shallow reflection horizon interpreted as the Holocene shoreface ravinement, exposing lag deposits that were truncated at the scarp and forming a thin high-backscatter anomaly. Up to 1.0 m of material was excavated shoreward of the scarp, including up to 0.5 m of shoreface sand above the shoreface ravinement, and another 0.5 m of indeterminate lithology below, consisting of easily erodible material. A second survey, in May 2010, found that the scarp had migrated seaward by up to 100 m and the depth of erosion indicated by the scarp had reduced to approximately [Formula: see text]. In a May 2013 survey, the scarp was no longer in evidence. The initial erosional event is interpreted to be caused by the ebb flow of the storm surge across the peninsula compounded by high-wave orbital velocities in the waning storm. This erosional event and its subsequent evolution demonstrate an impact on the shoreface lasting for years post-storm, as the shoreface gradually adjusted to a new equilibrium profile. These results document that an advancement of a shoreface ravinement can be caused by a single large event (e.g., tropical storm or hurricane) in this microtidal, relatively low wave energy setting. This process, tracked with near-surface geophysical techniques, was a key but seldom-observed component of the back stepping of barrier islands during sea-level rise.