The loss of ice and snow from a glacier system. This occurs through a variety of processes including melting and runoff, sublimation, evaporation, calving, and wind transportation of snow out of a glacier basin. All processes that remove snow, ice, or water from a snowfield, glacier, etc., that is typically melt, evaporation, sublimation as well as wind erosion, avalanches, calving, etc.; in this sense, the opposite of accumulation. In many publications before 1980, ablation did not include mechanical removal of either snow or ice, i.e., wind erosion, avalanches, calving, etc.