Features of Glacial deposition Examples from the Isle of Arran
A View of Glen Chalmadale Looking North West Lochranza Outwash Plain Till, filling the valley floor Mill Hill An Esker, a medial moraine or a protalus rampart? Loch A’Mhuillin A Kettle hole lake
Glen Rosa Moraines • Glen Rosa contains many fine examples of glacial moraines, these were deposited as a result of the Loch Lomond Stadial (the Loch Lomond readvance). Here we can see the terminal moraine from this advance in the foreground and a recessional moraine produced by a temporary advance during the final retreat of the valley glacier. Lateral moraines can also be seen further into the valley. Recessional moraine Rosa Water misfit stream Terminal moraine
Glen Rosa Terminal Moraine • This terminal moraine was deposited as the valley glacier from the Loch Lomond Stadial reached its furthest advance down into Glen Rosa. The moraine is composed of a typical jumble of boulders, cobbles and stones contained in a fine matrix of abraded material. The unsorted material is angular, showing little or no evidence of attrition.
Pro Glacial Lake deposits • It is believed that as the ice in Glen Easan decayed, the mouth of Easan became blocked at the baked margin and a pro-glacial lake formed at the bottom end of the Glen. It has been suggested that the thin laminated deposits here are varves. • Varves are paired layers of sediment, a coarse sandy layer deposited in spring and early summer when melt water stream energy is high. In autumn and winter the competence of the meltwater streams decrease and finer material is carried and deposited in the lake. Thin differentiatedlayers alternately light and coarse and dark and fine
Glacial Outwash Plains • These are large areas of sediment of glacial origin deposited by meltwater streams at the furthest distance from the glacier snout. They are formed from gravels, sands and clays (the clays being deposited at the furthest distance from the snout). Material already deposited by older streams and ice activity may be reworked and sorted by the streams forming the outwash plain. One possible explanation for these well sorted deposits at the mouth of Glen Catacol is that they were part of an outwash plain created by the melting ice in this large glacial valley.
Glen Rosa Outwash Plain • The flat area at the mouth of Glen Rosa became a large outwash plain as the Loch Lomond ice melted. • The sands and gravels have been commercially exploited to the extent that the company which quarries the deposits sells the sand to Saudi Arabia.
Braided Streams • When glacier ice melts, the water flows away from the glacier snout in fast flowing streams and rivers. This meltwater transports vast quantities of sediment and larger debris. If the sediment load is very large in relation to the velocity of the stream, the coarse material may start to block the stream channel, choking it and forcing it to constantly change its course. The stream starts to diverge, splitting into segments which split and rejoin repeatedly. • This example is near to the mouth of Glen Catacol.
Hummocky Morainal Topography A ‘catch all’ term used to describe extensive areas of uneven moraine covering flat areas at the mouth of valley glaciers or across the plains formerly covered by ice sheets. The moraine here at the mouth of Glen Easan is probably a mixture of ground moraine, predominantly lodgement till.