|Glacial diversion of drainage
In the northern Cairngorms, the Water of Caiplich and the Avon both show well-developed elbows of capture as they turn to flow N (Linton, 1954). These river systems were part of the Don catchment before glacial diversion. The orientation of the new, narrow valleys lies to the NE and this suggests that diversion was achieved by headward erosion of major meltwater channels beneath one or more ice sheets that flowed in this direction. In consequence, the Don has lost a large part of its headwater drainage system. The Ailnack Gorge is particularly spectacular.
The relative youth of the valley sections NE of the elbow of capture is attested by the rock slope failures along their sides and the proximity of knick points on the tributary streams to the main valley.
Major landslip on the left bank of the Avon, flanks of Sr˛n Gharbh
In the southwest Cairngorms, the Feshie breach was investigated by Linton (1949). The high benches on the north side of the upper Feshie indicate that the Feshie was formerly the headwater tributary of the Dee. During the Quaternary, the ice that accumulated in the Geldie basin flowed to the NW and to the E. The flow to the northwest led to over-deepening of the existing open valley and a reversal of drainage in the upper Geldie and the diversion of its headwaters to the Feshie and Spey systems.
The main glacial breaches of the Cairngorms - the Lairig Ghru, and the Lairig an Loaigh - are members of a suite of N-S oriented valleys that are cut though preglacial watersheds. Such breaching requires a substantial ice cap over the Cairngorms. The northerly orientation of these breaches suggest that the main phases of erosion occurred when Cairngorm ice was free to flow in this direction.
Google Earth image of the Ailnack Gorge
Elbow of capture of the Ailnack upstream of The Castle
Incised, narrow valley of the middle Avon, north of Inchrory