How do eskers form beneath melting ice sheets?

Eskers are long, winding ridges formed by the deposition of stratified sand and gravel within subglacial or englacial tunnels.12

These features originate when meltwater streams flow through tunnels located beneath or within a glacier. As these streams transport and deposit sediment along their channels, they create linear deposits. The formation process is typically associated with stagnant ice; as the glacier retreats and the ice eventually melts away, these channel deposits are "let down" onto the ground surface, leaving behind the characteristic sinuous ridges. Because the movement of active ice would likely disperse the material and create ground moraine, eskers are primarily preserved after the ice has ceased its forward motion.12