CORE UNIT: PATTERNS AND PROCESSES IN THE PHYSICAL ENVIRONMENT
IN DEPTH – Moraines Freeze-thaw action on the mountainsides above the ice created debris which fell onto the top and sides of the glacier. This debris added to the plucked material and was held close to the valley side by the ice. Once the glacier melted this debris fell to the ground at the valley sides, blanketing it in a gently sloping ridge of unsorted stones and boulders called lateral moraines. Englacial and ground moraine as well as medial moraine are carried to the snout of the glacier and deposited there as end moraines. Meltwater streams flow through and out of this end moraine. The very large South Ireland end moraine sweeps across Ireland in a crescent shape from South Wicklow to the Shannon estuary. As the ice melts, the glacier retreats. When it stops it will start depositing smaller
ridges of debris at the front. These are recessional moraines. Medial moraine: This ridge of debris is formed where two lateral moraines meet at the junction of two glaciers. Large glaciers may have many medial moraines visible as dirty- looking stripes on their surface. The moraine is carried further down the valley by the main glacier until it is deposited at the front (snout) of the glacier. End (terminal) and recessional moraines:An end moraine is a crescent-shaped ridge of debris, which marks the furthest point reached by the ice.
Drumlins
Main processes: plucking, melting, friction, deposition. Example: County Monaghan These landforms are small, oval-shaped hills made from boulder clay (‘drum’ meaning small hill). They range in size from 25 to 100 metres high , 0.5 km wide and 1 km long. One end is steep (known as the stoss side) and faces the direction of ice movement, the other end has a gentler slope (the lee side). In Ireland the drumlin belt runs from Strangford Lough, County Down to Clew Bay, County Mayo.
IN DEPTH – Drumlins
Drumlins are formed beneath the ice when an ice sheet is heavily laden with boulder clay and is melting but still able to advance or surge. Friction between the ground and the ice causes the load to be deposited. As the ice advances it moulds the deposited material into these distinctive egg-shaped mounds. Some drumlins have a large boulder at their centre and are called rock drumlins.
Rock drumlins form where the large boulder causes extra friction as it gets in the way of the ice, causing deposition around it. Drumlins tend to occur in large groups called swarms and the resulting landscape is often called a basket of eggs landscape.
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