The distinctive parallel lines running the length of Glen Roy may look mysterious but actually provide evidence for ice-dammed lakes at the end of the last glaciation
Glen Roy is home to a curious, distinctive set of three parallel, horizontal lines running along the length of the hillsides. Glen Gloy and Glen Spean host similar, though less dramatic features, but it is in Glen Roy that some of the greatest thinkers of all time set their sights on understanding what had created these strange ‘parallel roads’.
Before geologists had unravelled the story of Ice Ages in Scotland, many thought that the ancient Kings of Scotland or even Fingal the mythical Celtic hero had built these ‘roads’. On Ordnance Survey maps they are marked as tracks! Charles Darwin visited the area in 1838 and was ‘amazed’ by the roads – he, along with geologist Charles Lyell, thought they were old marine shorelines formed when the sea reached much further inland. It was only later in the 19th century that glacier expert Louis Agassiz proposed the first theories involving the influence of glaciers on the landscape.
We now know that the ‘parallel roads’ are in fact shorelines created by ice-dammed lakes. Glaciers spreading from the south-west during the Loch Lomond Stadial cold spell, which began around 12,900 years ago, blocked off the normal river drainage systems from Glens Gloy, Spean and Roy, forcing them to overflow to the east and into the Spey River system. As the ice front advanced, successive overflow channels were dammed off, forcing higher overflow channels to be used. These glacially-dammed lakes are responsible for the ‘Parallel Roads’ shorelines, representing successive heights of the water at 260, 325 and 350 metres above sea level. When the ice dams finally melted, about 11,500 years ago, the drainage of these lakes was catastrophically sudden.
Glen Roy today clearly demonstrates a wide range of geomorphological features, including glacial moraines, deltas, river floodplains, terraces and bluffs, alluvial fans and landslips. The Dalradian meta-sedimentary bedrock underlying Glen Roy also shows through in places.
It is no wonder that Glen Roy is a National Nature Reserve for the promotion and protection of these relatively ephemeral, superficial, periglacial landscape features.
Text contributed by Jim Blair, Lochaber Geopark
Find out more
Access: Glen Roy can be accessed from the A86 Spean Bridge to Newtonmore road, turning off at Roy Bridge (Grid Reference NN 269 813). There is a road sign, ‘Ice Age Landscapes’, directing visitors to a single track road up Glen Roy, and a visitor centre and café at Roy Bridge, run by Lochaber Geopark. Currently, Glen Roy is a National Nature Reserve, but there is no signage to that effect. There is a car park and viewpoint approximately 5 kms up the Glen. The public road then continues for another 5 kms to a car park and turning area. An estate road then allows pedestrian traffic on to the upper reaches of Glen Roy. The National Nature Reserve extends from the viewpoint to the turning point car park.
Dalradian Metamorphic Rocks: You can see good exposures of the Brunachan Psammite Formation below the farm bridge at NN 330 909 beside the road. These are psammites and flaggy semi-pelites, showing small-scale folding within the beds.
“Charles Darwin and the Parallel Roads of Glen Roy”, visitors’ leaflet, Lochaber Geopark.
“Glen Roy”, Lochaber Geotrails leaflet, Lochaber Geopark.
Glen Roy A Landscape Fashioned by Geology, Peacock, D, Gordon, J and May, F, British Geological Survey and Scottish Natural Heritage (SNH), 2004. Download pdf from https://www.scottishgeology.com/find-out-more/publications/#glen_roy
Glen Roy National Nature Reserve: https://www.nature.scot/enjoying-outdoors/scotlands-national-nature-reserves/glen-roy-national-nature-reserve
“The Quaternary of Glen Roy and Vicinity”, Field Guide, Editors Palmer, AP, Low, JJ and Rose, J, Quaternary Research Association, 2008. An excellent, if academic, pocket field guide.
Proceedings of the Geologists’ Association Special Issue “The Lateglacial and early Holocene history of Glen Roy, Lochaber, western Scottish Highlands”, Palmer AP, et al, Volume 128, Issue 1, 2017. A brilliant, detailed account.
British Geological Survey; “Glen Roy” Map S63W (Solid and Solid/Drift versions) 1995, and Sheet Memoir S63W, “Glen Roy District”, Key, RM, 1997. Detailed bedrock and Quaternary geology.
This web page is published by the Scottish Geodiversity Forum under a Creative Commons ‘Attribution Non-commercial’ (CC BY-NC) licence, which permits non-commercial reuse provided the original work is properly cited.