Ice–ocean interactions at Greenland Ice Sheet outlet glaciers exert critical control on ice-sheet mass loss and, consequently, global sea-level rise. The GEOEO North of Greenland 2024 icebreaker expedition acquired a breadth of data in the unsurveyed Victoria Fjord, north-western Greenland, to assess the causes of the rapid break-up of the C.H. Ostenfeld ice tongue in 2002, and the environmental changes since. The observations reveal inflows of warm (>0 °C) Atlantic water reaching the grounded ice margin. We propose that Atlantic warm water pulses entering the Arctic Ocean reach north-western Greenland, where they interact with glacier fronts, enhance ice discharge, and amplify the climate-driven retreat of marine-terminating glaciers. The collapse of C.H. Ostenfeld’s ice tongue, unlike the slower retreats of the ice tongues of neighbouring Petermann and Ryder glaciers, reflects unimpeded Atlantic water inflow due to the absence of a shielding bathymetric sill, a function of the region’s bedrock geology.