4The Ice AgeThe oldest rocks in the NW Highlands Geopark are about 3,000 million years old: the youngest are 430 million years old but it is probably only in the last 2 million years that this spectacular landscape has taken on its now familiar appearance.And it is only 11,000 years since the last glaciers melted in this part of Scotland: a mere blink of an eye in geological time!The legacy of the Ice Age is everywhere, and the landscape owes much to it and the action of ice on the different rock types in reaching its present form.How do we know? Because the ice left clues in the landscape: deep U-shaped valleys and fjords; streamlined ice-worn bedrock; corries; arêtes, erratics, moraines and more.
6Processes of glacial erosion The three steps of glacial erosion are:Freeze-thaw:Bedrock beneath glaciers form cracks along planes of weakness. Water enters these cracks and freezes to form ice, which takes up more room. This forces the cracks wider. The water thaws and refreezes, again and again, further widening the cracks and eventually loosening fragments of rock.Plucking:As a result of freeze-thaw, the loose fragments are picked up and pulled away by ice and embedded into the base of the glacier as it moves downhill.Abrasion:Fragments carried in the base of glaciers grind in to the bedrock just like sandpaper on wood. This grinding leaves long grooves called striations if the debris is coarse or smooth polished rock surfaces if the debris is fine.
23Acknowledgements Authors Rod Owen (British Geological Survey) Tom Bradwell (British Geological Survey)Jackie Yuill (Perth Academy)Murdo MacPherson (Kinlochbervie High School)Special thanks toPaul Ewing (Arbroath High School)Maarten Krabbendam (British Geological Survey)Isobel MacPhail (North West Highlands Geopark Development Officer)This CD has been produced with co-funding from the Royal Scottish Geographical Society (RSGS).CD cover artwork by Miranda MacDonald (Kinlochbervie High School).Rod Owen and Tom Bradwell publish with the permission of the Executive Director of the British Geological Survey (NERC).