The vast majority of the meltwater from the surface of the Greenland ice sheet descends through fissures and cracks to the base of the sheet over a kilometer below. The gravitic potential energy as well as the friction experienced by the flow is converted almost entirely to massive amounts of thermal energy that is melting the ice sheet from the bottom at a tremendous rate.
Accelerating melt rate makes Greenland Ice Sheet world's largest 'dam'
Researchers have observed extremely high rates of melting at the bottom of the Greenland Ice Sheet, caused by huge quantities of meltwater falling from the surface to the base. As the meltwater falls, energy is converted into heat in a process like the hydroelectric power generated by large dams.
phys.org