Drumlins are oval-shaped hills made of boulder clay.
Formation: • A drumlin forms when a glacier deposits mounds of boulder clay.
• The glacier then continues its journey and smooths the boulder clay as it moves over it.
• The steep slope or stoss end of the drumlin shows us what direction the glacier was coming from. The gentle slope or lee slope shows us what direction the glacier was travelling in.
• Drumlins usually occur in clusters, forming what is called a ‘basket of eggs’ landscape.
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Steep slope
Side view Direction of glacier movement Boulder Clay Gentle slope
View from above : Figure 11.16 How a drumlin is formed Examples of drumlins: Clew Bay in Co. Mayo and Strangford Lough in Co. Down. 89 87
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88 : Figure 11.17 Drumlins in Clew Bay, Co. Mayo, on an OS map
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84 : Figure 11.18 Drumlins in Clew Bay
Erratics
Erratics are large boulders that were transported from their original location by a glacier and then deposited in an area where the rock type is different.
For example, there are boulders of granite in the Burren, Co. Clare, where the local rock type is limestone. The nearest source of granite is north Galway, which tells us that the ice sheet that passed over the Burren came from the north.
: Figure 11.19 An erratic in the Burren, Co. Clare 185
