Glen Roy

Glen Roy, near to the Great Glen, has various glacial features, but is undoubtedly most famous for its striking parallel ‘roads’. These ‘roads’ are the remnant shorelines of a glacial lake that existed in the glen during the last phase of glacial activity (the Loch Lomond Stadial). There are three levels of parallel ‘roads’ in the glen, all indicating different lake levels. Others can be found in nearby Glen Gloy, but only at one level. These features are unique in Britain for their excellent preservation, and for the fact that they are partly cut into the bedrock.

Following the end of the last ice age during the Late Devensian (approximately 13,000 years ago), there was a cold spell known as the Loch Lomond Stadial (approximately 11,000 to 10,000 years ago). During this time, glaciers readvanced through the Highlands. At Glen Roy, the glaciers advancing from the south and west dammed a glacial lake in the valley. The lake existed long enough to form shorelines high on the slopes of the valley. The partial incision into the bedrock is thought to have resulted from frost action caused by the arctic climatic conditions, although this is only at localities where the bedrock is flaggy, schistose or already partly weathered. The advance and retreat of the glacier front has formed three levels of parallel roads: 250m, 261m and 325m above OD. The outlet for the lake lay to the northeast.

Other important glacial landforms exist in Glen Roy, formed during the Late Devensian ice age. These include the deposition of moraines, outwash fans, erratics and the occurrence of landslips. It is also thought that earthquake activity accompanied the retreat of the Loch Lomond Readvance.

Glen Roy showing some of the parallel ‘roads’ - the ‘roads’ are the remnant shorelines of a glacial lake that existed in the glen during the last phase of glacial activity (the Loch Lomond Stadial). © Scottish Natural Heritage.

Further reading:

Gordon, J.E. & Sutherland, D.G. 1993. Quaternary of Scotland, Geological Conservation Review Series No. 6., Joint Nature Conservation Committee, Peterborough.

Peacock, D., Gordon, J.E. and May, F. 2004. Glen Roy – A Landscape Fashioned by Geology. Produced by: Scottish Natural Heritage & British Geological Survey.

Stephenson, D. & Gould, D. 1995. British Regional Geology. The Grampian Highlands. 4th edn. British Geological Survey (Her Majesty’s Stationery Office, London).