These are moraines, often composed of till. These are relatively low, smoothly rounded, oval hills with a steeper face (stoss side) upstream. The long axis of these features are parallel to the direction of movement of the glacier. Drumlins may have the length ranging from a few hundred metres to 1 or 2 Kilometres and in height they may range from 10 to 60 metres. They are usually two to three times as long as they are wide. Each drumlin resembles the inverted bowl of a spoon.
Drumlins are invariably found in a zone behind the terminal moraine. They always tend to occur in groups which may number in the hundreds; single drumlins are rare. The topography thus produced is called a basket of egg-topography.
Drumlins are formed beneath the moving ice when the clay-rich debris is abundant near the base of an ice-sheet. As a result, any knob-like obstruction in the path of the ice gets plastered above and around with dense clay and boulders, which are then moulded into a low streamlined hill called a drumlin.
Thus a bedrock core is often observed at the middle of the drumlin. The blunt end of a drumlin faces the direction from which the ice flowed and thus serves as an indicator of direction of ice movement.
ADVERTISEMENTS:
Drumlins are mainly associated with Continental ice-sheets and show features opposite to those of roches mountonnees.