Terrestrial radar observations were used to investigate flow speed changes at Eqalorutsit Kangilliit Sermiat, a marine-terminating glacier in Greenland. The velocity varied on both daily and multi-day timescales, showing that the glacier speeds up markedly when meltwater or lake drainage increases basal water pressure. Usually speed changes move downstream with time towards the glacier front, but during multi-day speed-up events they start at the front and travel upstream.