Glacial Landforms of Deposition (Drumlins)

Definition and Formation of Drumlins

Drumlins are elongated hills formed by the deposition of glacial material, mainly till, which is a mixture of clay, sand, gravel, and boulders deposited directly by ice. They are created beneath moving glaciers or ice sheets when the ice reshapes and deposits sediment in streamlined forms aligned with the direction of ice movement.

The formation process involves the glacier pushing and moulding the soft sediment beneath it. As the ice advances, it deposits till and shapes it into smooth, oval hills with their long axis parallel to the flow of the glacier. This means drumlins provide important clues about the direction the ice was moving during the last Ice Age, specifically during the last glaciation period, known as the Devensian glaciation, roughly 10,000 years ago.

Drumlins are different from moraines, which are ridges of deposited material at the glacier’s edges or terminus, and from erratics, which are large boulders deposited by glaciers far from their source. Drumlins are specifically formed by the ice reshaping till beneath the glacier.

Characteristics of Drumlins

Drumlins have a distinctive shape and features that help identify them in glacial landscapes:

• Smooth, streamlined shape: They are elongated hills with a rounded, smooth surface, resembling an inverted spoon or a half-buried egg.
• Steep stoss side: The side facing the direction from which the ice came (up-ice) is steep and blunt.
• Gentle lee side: The side facing the direction the ice moved towards (down-ice) slopes gently away, tapering off.
• Occur in groups or swarms: Drumlins rarely appear alone; they often form clusters or fields called drumlin swarms, showing consistent ice flow direction over a wide area.
• Composed of till: The material making up drumlins is till, a mixture of clay, sand, gravel, and boulders, which is compacted and shaped by the glacier.
• Size: Drumlins typically range from 200 to 1,000 metres in length and up to 50 metres in height.

These features make drumlins useful for interpreting past glacial environments and ice movement patterns.

Examples in the UK

Drumlins are found in several parts of the UK, especially in areas once covered by ice sheets during the last Ice Age:

• Lake District: This upland area has many drumlins formed by the movement of ice across the region, contributing to its rugged glacial landscape.
• Yorkshire: Particularly in the Vale of York, drumlins form part of the rolling landscape shaped by glacial deposition.

These drumlin fields are part of the wider glacial landscape features that include other depositional landforms like moraines and erratics, as well as erosional features (covered in other topics).

The presence of drumlins in these areas reflects the direction and extent of ice sheet movement across the UK during the last glaciation, roughly 10,000 years ago.

Significance and Uses

Drumlins are important for several reasons:

• Indicate ice flow direction: Their shape, with a steep stoss side and gentle lee side, shows the direction the glacier moved. This helps geographers and geologists reconstruct past ice movements.
• Influence local drainage patterns: Drumlins can affect how water flows across the landscape, creating small lakes or influencing river courses by acting as natural barriers.
• Used in agriculture and land use planning: The soil on drumlins is often fertile due to the glacial till, making them suitable for farming. Their shape and drainage also influence how land is used, including settlement and transport routes.

For example, farmers may use the well-drained slopes of drumlins for crops, while the flatter areas between drumlins might be used for pasture.

Understanding drumlins also helps planners avoid building on unstable ground or areas prone to flooding due to altered drainage.

Learning Example: Interpreting Ice Flow Direction from Drumlins

If you see a drumlin with a steep side facing northwest and a gentle slope facing southeast, the glacier moved from northwest to southeast. This is because the steep side (stoss) faces the direction the ice came from, and the gentle slope (lee) points the way the ice was moving.