Glen Roy

Glen Roy in the Lochaber area of the Highlands of Scotland is a National Nature Reserve and is noted for the geological puzzle of the three roads ("Parallel Roads"), which are preserved ice-dammed lake shorelines, from a brief (some 900-1,100 years in duration), climatic deterioration, during a much longer period of deglaciation, subsequent to the last main ice age (The Devensian). From a distance they resemble man-made roads running along the side of the Glen, hence the name.

Location and access

The glen runs north from Glen Spean which takes the main A86 trunk road and the railway of the West Highland Line, both running about a further 14 miles southwest via Spean Bridge to Fort William. The village of Roybridge and Roy Bridge railway station are sited where the River Roy joins the River Spean, and from there a narrow single track road runs north up the glen for almost 10 miles to Brae Roy Lodge.

The Parallel Roads of Glen Roy

The Parallel Roads of Glen Roy, Scottish Highlands, represent a series of ice-dammed proglacial lake shorelines produced during the cold climate of the Younger Dryas (GS1). It has been demonstrated by "Dawson, Hampton, Harrison, Greengrass and Fretwell (2002)" that each lake shoreline exhibits evidence of glacio-isostatic tilting associated with the decay of the last (Late Devensian) ice sheet. The directions of tilting of the three shorelines (in the quadrant between north and east), are at variance with published glacio-isostatic uplift isobases based on marine shoreline data that suggest a pattern of decreased uplift towards the northwest. The gradient of shoreline tilting (between 0.11 and 0.14 m km-1) is similar to measured regional tilts of a well-developed marine shoreline (the Main Rock Platform) considered to have been produced in Scotland during the same period of extreme cold climate. Consideration of the ice-dammed lake shoreline data also points to the former occurrence of two separate episodes of tectonic activity during the Younger Dryas (Greenland Stadial 1 - GS1).

Historic geological investigations

In the 19th century, the Parallel Roads attracted the attention of many early geologists, including the Reverend William Buckland, James Geikie, Charles Darwin, Charles Lyell and Joseph Prestwich. This interest ensured that the Parallel Roads featured prominently in the development of geological science.

Darwin made his "Gigantic Blunder" on his visit in June 1838 by drawing on his recent findings in South America during the "Beagle" expedition and believing that the shorelines were of marine origin. This was contradicted by Louis Agassiz's Glacial theory of 1840 which postulated that the shorelines had been cut by freeze-thaw processes of lake ice during the maximum extent of glacial ice in the climatic reversal known as the Younger Dryas / Greenland Stadial 1 or locally the Loch Lomond Readvance.

Four decades after his 1839 paper and shortly before his death, Darwin conceded that he was incorrect. However, he had conceded that he was embarrassed by "that confounded paper of mine" as early as 1861, in letters to Thomas Jamieson, quoted by Jamieson (1863; 1892).

Interest in the Parallel Roads continues to this day, both among earth scientists intrigued by the dramatic processes that shaped that landscape, and among tourists attracted by the natural wonder of the landforms.

References

* [http://www.snh.org.uk/publications/on-line/geology/glen_roy/ SNH Publications - Landscape Fashioned by Geology - Glen Roy]
* [http://www.undiscoveredscotland.co.uk/roybridge/glenroy/index.html Glen Roy feature page on undiscovered Scotland]
* [http://darwin-online.org.uk/content/frameset?itemID=F1653&viewtype=text&pageseq=1 Observations on the Parallel Roads of Glen Roy, and of other parts of Lochaber in Scotland, with an attempt to prove that they are of marine origin. By CHARLES DARWIN, Esq., M.A. F.R.S. Sec. G.S] (1839)