Limited data on the past dynamics of the Greenland Ice Sheet, exceeding the ice-core records, have led to partly contradictory reconstructions. Whereas the Scoresby Sund sector of the Greenland Ice Sheet has been suggested to be stable and not much larger than at present during the peak Pleistocene glaciations, the southeastern sector of the ice sheet has been inferred to be much more dynamic. Here we present seismic data showing that glacigenic debris-flow deposits dominate the younger than ca. 2.58 Ma succession of the Scoresby Sund trough mouth fan on the East Greenland continental margin, suggesting much more frequent expansions of the Greenland Ice Sheet to the shelf break than found previously. From our new observations of the Pleistocene stratigraphy, we revise previous findings and conclude that the Scoresby Sund sector of the Greenland Ice Sheet during the Pleistocene (1) developed in line with other parts of the East Greenland Ice Sheet, and (2) was more dynamic and sensitive to past climatic changes than hitherto realized. This rapid response of the glacier to climate forcing indicates how dynamic is the glacier ice front and what one might expect of the glacier as the influences of climate warming become more pronounced.