What is a drumlin and how does it develop?

A drumlin is an elongated hill formed by glacial ice acting on underlying till or ground moraine.

Drumlins are typically found in clusters known as drumlin fields and are often shaped like an inverted spoon or a half-buried egg. They are formed under the ice of a glacier, which shapes the underlying sediment into these streamlined hills. The long axis of a drumlin is aligned in the direction of the glacier's movement, with the steeper end facing the direction from which the ice came and the gentler slope pointing in the direction the ice was moving.

The formation of drumlins is still a topic of scientific research, but it is generally believed that they form through a combination of processes involving the deposition and reshaping of sediments by glacial ice. As the glacier moves, it exerts pressure on the sediments beneath it, compacting and moulding them into the characteristic drumlin shape. Some theories suggest that drumlins form when the glacier encounters an obstacle, causing the ice to flow around it and deposit sediments in the process. Others propose that they result from the melting and refreezing of ice at the base of the glacier, which helps to shape the sediments.

Drumlins can vary greatly in size, typically ranging from 250 to 1,000 metres in length, 120 to 300 metres in width, and 15 to 50 metres in height. Their composition can also vary, with some drumlins being made up of till (a mixture of clay, sand, gravel, and boulders) and others consisting of more sorted materials like sand and gravel.

Understanding drumlins is important for geographers because they provide clues about past glacial movements and the dynamics of ice sheets. By studying drumlin fields, scientists can infer the direction, speed, and behaviour of ancient glaciers, which helps to build a picture of Earth's climatic history.