25,000 years ago northern England was covered by around 700 metres of ice at the ‘glacial maximum’ of the Late Devensian Ice Age. The erosional forces of powerful glaciers, flowing south from the Lake District, moulded our landscapes. Glacial retreat occurred locally around 18,000 years ago when the climate warmed and left a legacy of depositional features which include oval shaped hillocks called drumlins. The Trust’s new land at Coldwell is almost wholly composed of a drumlin.
Drumlins are formed under glaciers and their alignment follows the direction of ice flow. A 2008 study of 58,983 drumlins in Great Britain and Ireland showed a mean length (L) of 629m, width (W) 209m and elongation ratio (E or L/W) 2.9. The Coldwell Drumlin has a length of 350m, a width of 155m and an elongation ratio of 2.2. Although these figures are below the mean, they are well within the common dimensional ranges for length (250-1000m), width (120-300m) and elongation (1.7-4.1).
Ice Flow
The drumlin is aligned SSW following the direction of glaciers as they flowed across the land that later became the Arnside and Silverdale AONB. Many drumlins, but not all, have a steeper, stoss slope up-ice with a gently descending lee slope down-ice and the highest point is usually close to the stoss end. Our drumlin does not follow this common pattern and its 107ft (32.6m) summit is located towards the southern down-ice end, perhaps because the glacier was flowing gently uphill at this point.
Drumlins are composed of glacial till which is unsorted glacial sediment that has been entrained and transported by the glacier before deposition during ice retreat. The many rocks in the till are mainly Silurian greywackes from the Windermere Supergroup. Those exposed on the surface were a nuisance for farmers and were often cleared from fields into heaps or cairns or used to build walls. There are plenty of examples around the Coldwell Land.
Why are there no trees?
In parts of Coldwell Parrock and Coldwell Meadow limestone bedrock is sometimes exposed and elsewhere is usually not far below the surface. But across the drumlin the soils are deep which would have made arable farming easier and it may well be that ploughing dates back to medieval times. A long history of ploughing could partly explain why the new reserve has no trees in contrast to the neighbouring land.
Drumlin Swarms nearby
Drumlins often occur in swarms and the best local example, at Crooklands, is described in the Farleton and Hutton Roof Geotrail.
