Daily discharge rates vary because at night the meltwater flowing through the glacier freezes, thus lowering discharge. During the day this frozen water begins to thaw and reaches peak discharge in the afternoon. This is why in the morning near a glacier one may be able to cross a stream with no difficulty, while in the afternoon there is no way to cross the stream because the discharge is too high. Drainage of Meltwater Drainage of glacial meltwater can occur in three different places on or within the glacier. Supraglacial drainage occurs on top of the glacial ice.
Englacial drainage occurs within the ice, and subglacial exists beneath warm based glaciers.
Supraglacial drainage is most common in the ablation area of the glacier. For surface drainage to occur the surface must melt more water than can be absorbed by the ice. Stream channels usually form from slush swamps, where free meltwater ponds into a slushy swamp. Eventually this swamp grows and the water within the swamp begins to run off the glacier. The stream channels draining the glacier are usually of a dendritic pattern.