The weight of the overlying ice creates differing pressures in the ice. The water will find the path of least resistance. Subglacial Water in subglacial channels flows in response to atmospheric pressure where it is open to the atmosphere, as well as to cryostatic pressure where it is closed off from the atmosphere. There are a variety of different ways water can exit the subglacial system. They are subglacial channels that are seen as ridges on the landscape after a glacier has retreated.
Eskers flow from areas of high potential to low potential.
They are an indication of the location of the equipotential lines in a glacier. When eskers are closed off from the atmosphere and respond to changes in cryostatic pressure, they will flow over ridges, and not follow topography. The shape of the esker in the ice is a function of the pressure gradient. Sharp crested eskers Debris is deposited along the sides of the channel where the flow velocity is the lowest. Preferential melting of the crest of the channel carves out the top.