truncated spurs on Orkney

selective linear glacial erosion

corries

valleys

roches moutonnées

glacial erratics

depositional forms

glacial diversion of drainage

             © Gavin Shaw 

Bod an Deamhain is the original Gaelic name for this hill but the  Victorian cartographers avoided the most fundamental translation by using a euphemism.

A glance at the map shows that this truncated spur is also a good example of a former dome that has been deeply eroded by ice.

Truncated spurs on the western flank of the Lairig Ghru glacial breach

 

The spur originally took the form of an oval dome. Glacial erosion along Glens Geusachan and Dee has not only truncated the spur but also consumed all but a quarter of the original dome.

 

 

The eastern cliff of the truncated spur above the breach of the Lairig Ghru.

Truncated Spur

Definition: A blunt-ended, sloping ridge which descends from the flank of a valley. Its abrupt termination is normally due to erosion by a glacier. Glaciers tend to follow straighter courses than rivers.

 

The Devil's Point in upper Glen Dee is perhaps the finest example of a truncated spur in the Cairngorms. The original spur protruded into the preglacial valley of the upper Dee and its end has been truncated by the passage of ice down the Dee valley. The glacial cliff is 400 m high. 

truncated spur

The curved sheet jointing that controls the dome shape is evident on its NW flank. Glacial erosion has not only removed the former east end of the dome. Ice moving down Glen Geusachan has also undercut and steepened the southern flank of the dome. The result is that the dome now resembles a quarter of an egg in its form.