Glen Roy
Gleann Ruadh
Lochaber is famous for the mysterious parallel lines that can be traced along the sides of Glen Gloy, Glen Roy and Glen Spean. The best examples of the ‘parallel roads’ are found in Glen Roy.
Before geologists unravelled the story of ice ages in Scotland, many people believed that the lines were roads built by the ancient kings of Scotland. It was only in the 19th century that the first theories about glaciers were put forward. We now know that these ‘roads’ are in fact shorelines created by ice-dammed lakes.
The six stopping points on the geotrail reveal more about the formation of the glen and its famous ‘roads’.
1. View of the riverbed – Sealladh den bhun-creige
A short walk to a bridge offers a good view of a riverbed, showing some of the bedrock in this area. The pale coloured rocks were once sandy sediment in a shallow sea. This sediment was metamorphosed into a much harder rock called quartzite, and the steep layers of rock you can see in the riverbed today were tilted into position during the formation of the Caledonian mountains 460 – 430 million years ago.
2. Landslip – Beum-slèibhe
Make your way back down the glen to see a very recent change to the glen’s landscape. After heavy winter rains in 1989/90 water burst through an old landslip to create a thick porridge-like surge of mud and gravel that swamped the road and flowed into the river.
3. Viewpoint – Àite-seallaidh
Stop at the viewpoint to get the best views of the Parallel Roads. The last glacier that pushed up Glen Roy reached just beyond the viewpoint. As ice blocked its normal escape route, water built up in a natural reservoir inside the glen. The water reached an initial level of 260 metres before finding an escape route, but it was at this level long enough for the wave action to carve a shoreline, which we see as the lowest ‘road’. When the water’s escape route again became blocked the water level rose again, creating a new shoreline at 325 metres. This process was repeated and the water finally rose to its highest level and created a shoreline at 355 metres before eventually draining away.
4. Grey Corries – Beantann Glas
As you head back down Glen Roy look south for a view of the scooped-out corries on the mountains in the distance. These too were carved out by glaciers. The white quartzite rock that gives these mountains their pale colour was originally deposited as a pure quartz sand on an ancient sea floor. The loose scree now coating the summits was formed when these peaks stood out above the blanket of ice and were subjected to freeze-thaw cycles.
5. Jokulhlaup
During the final draining of Glen Roy the dam that created the lowest of the Parallet Roads burst in a spectacular Jokulhlaup (a sudden outburst flood from a glacial lake). It is estimated that around 5 cubic kilometres of water escaped under the ice through the Spean Gorge and into Loch Ness, before flowing out to sea at Inverness.
6. Moraines - Moraine
Along the road between Spean Bridge and Fort William there are many clues to the area’s glacial past. About 5km from Spean Bridge look out for a prominent ridge of glacial moraine on the left of the road. Ridges like this one are made from rock debris that was pushed along at the end of glaciers. This moraine was left behind when the glacier that once blocked Glen Roy retreated back down the Great Glen.
