5. Glacial transportation and deposition - Drumlins

Question 1

Describe what a Drumlin is/its appearance.

Answer 1

The term drumlin is derived from the Gaelic word druim, meaning a rounded hill. The main features of Drumlins are:

• they are smooth, oval-shaped small hills, often resembling the top half of an egg
• they can be as long as 1.5km (although most are much smaller) and up to 50-60m in height
• they have a steep end known as the **stoss **and a gently sloping end, the lee
• they are elongated in the direction of ice advance with the stoss at the upstream end and the lee at the downstream end
• they are often found in groups known as **swarms **and, given their shape, this is sometimes referred to as a ‘basket of eggs topography’
• they are formed from unsorted till
• they are found on lowland plains such as the central lowlands of Scotland. A well-known swarm is at Hellifield in the Ribble Valley, Yorkshire. Many are found at the lower end of glacial valleys

Question 2

Explain the formation of a Drumlin.

Answer 2

There is some controversy over the origin of Drumlins, which are formed underneath the ice. The most widely held view is that they are the result of the ice being overloaded with debris. This reduces its capacity to carry and depostion occurs at the base of the ice. Once this material has been deposited it is streamlined by further ice advance. There could also be pre-existing sediment (older till from a previous glacial advance, for example) that is caught up in the streamlining process.

• Look at Surge Theory (2010)