Grounding Line

The grounding line is the boundary where a glacier or ice sheet stops resting on bedrock and begins to float as an ice shelf or ice tongue. Its position is set by the balance of ice thickness, bed elevation, and ocean buoyancy, so it migrates with sea level, ice thinning, and ocean heat reaching the cavity. Grounding lines on beds that deepen inland are prone to marine ice-sheet instability: once retreat begins, thicker ice fluxes across the line and can drive runaway retreat, as feared at Thwaites and Pine Island glaciers. Submarine melt and subglacial discharge concentrate at the grounding line, and its migration is tracked with CryoSat-2 and ICESat-2 elevation data.