The sources are surface meltwater, basal, internal, and groundwater. Each source of meltwater plays a crucial role in the mechanics of the glacier, and how the glacier releases the meltwater as discharge. Surface sources of meltwater accounts for the greatest amount of discharge from the glacier. Radiation refers to solar radiation, which will change with the season, time of the day, latitude, altitude, cloud cover, exposure, humidity, and albedo of the glacier. The amount of incoming solar radiation is a major factor in controlling the surface melt of a glacier.
Convection refers to the movement of air across the surface of the glacier.
Air that is next to the glacial ice will be quickly cooled to zero degrees Celsius. However, if convection is present, warm air will replace the cool air close to the surface of the glacier, and thus influence melt. Finally, condensation will influence the melting of glacial ice. If the relative humidity is such that the air is at dew point and is in contact with ice or snow, condensation will occur. Basal and internal sources of meltwater also contribute to the amount of water within the system of the glacier.