The Parallel Roads represent the shorelines of ice-dammed lakes. Typically they are narrow benches (several metres wide) cut into the bedrock of the hillsides and in places covered by remnants of lake beach gravel. They extend along much of Glen Roy and Glen Gloy and parts of Glen Spean. Probably they formed through a combination of intense frost weathering and wave action along the lake shore zone. The control of lake levels by the different cols allowed the lakes to persist for sufficiently long periods such that even the hard, Precambrian bedrock was broken up and eroded.
An ice field developed to the west of Glen Roy and the Great Glen, with a further ice centre to the south, over Rannoch Moor. Glaciers flowed eastwards along the glens from the ice field in the Western Highlands. One tongue of ice blocked the entrance to Glen Gloy, while another extended eastwards to block lower Glen Roy. Here it met a glacier that had extended into the middle section of Glen Spean. The blocking of Glen Spean led to a lake being impounded. As the glacier advanced up lower Glen Roy, it cut off a lake in this valley and the rising water eventually found its way across a pass.
A further advance of the glacier up Glen Roy resulted in the blocking of this exit for the water, and the lake rose further, to drain across the low ground at the head of the Roy and Spey glens. A lake at a higher level impounded in Glen Gloy drained through the head of this glen across a pass into Glen Roy. As the ice retreated, the overflows were unblocked in the reverse order; finally the ice dam broke near Spean Bridge and the lake drained away under the glacier very suddenly and rapidly towards the Great Glen.
To claim this cache you must answer two questions and submit a photograph of yourself with your GPS and the earthcache feature in view.
Question 1. What are the heights in metres of the three “roads”?
Question 2. What is the name of the glacier which dammed Glen Roy?
E-mail the answers to us via our profile. If we do not receive the answers and/or a photograph is not posted, you may have your log deleted. Educational guidelines for Earthcaches are set by Geocaching.com and GeoSociety.org (Earthcache) and have to be adhered to.