Lairig Ghru, looking south

Lairig Ghru, looking towards the Pools of Dee from Lurcher's Crag

Streetmap extracts North Middle South

The glacial breach of the Lairig Ghru viewed from the north. Google Earth image.

Glacial breach

Definition: a new valley cut beneath glacier ice through an ancient watershed

glacial valleys alps or valley benches troughs truncated spurs

diversion of drainage rock slope failures                                

A set of major glacial valleys have been cut though or breach the preglacial watersheds in the Cairngorms. The set includes the Lairig Ghru (A), the Saddle at the head of Strath Nethy (B), the Lairig an Loaigh (C) and its continuation to the N, Loch Builg (D), the head of the Gairn (E) and upper Glen Feshie (F). The Feshie breach is unusual in that it effected a reversal of the preglacial drainage.

In each case, the breaching has been caused by ice over-riding a structurally-controlled preglacial col. Apart from Glen Feshie, the breaches have a S-N orientation, implying that they were formed during periods when ice was free to flow towards the N. Breaching appears to postdate the main period of corrie formation, as there has been no significant development of these glacial hollows on the sides of the breaches. The breaches also seem to have attained much of their present form prior to the last ice sheet, as ice flow at that time tended to be transverse to these valleys. It seems that the breaches were cut mainly during the Middle Quaternary during periods when ice flowed N within them.

An aerial view of the Ghru from an old A Level examination paper, with the Devil's Point arrowed