Glen Einich,
looking south
Shelter Stone Crag
Stag Rocks, looking down from the trough head
towards Loch Avon
Google Earth image of the Gleann Einich trough viewed from the N
Gleann Einich, with trough head and corries above Loch Einich
Glacial troughs
Definition: a valley shaped by valley glaciers and ice streams within ice sheets that has a distinct trough form. The trough head is enclosed by glacial cliffs and may be overlooked by a extensive snow-gathering areas.
Glen Avon, looking south over Loch Avon and towards the trough head
The Cairngorms include two fine examples of glacial troughs: Gleann Einich and Glen Avon. The long profiles of these valleys can be described as 'down at heel' - the terrain drops steeply from the plateau down the trough head to a rock basin now filled with a loch up to 40 m deep. The location of the trough head and the basin reflects the convergence of ice flow and the way in which the increased ice discharge has led to over-deepening.
In upper Glen Avon, the Garbh Uisge Mhór cascades down the slabs of the trough head. The deepening of the valley by glacial erosion has rendered the surrounding cliffs unstable, causing major rock failures such as that which includes the Shelter Stone (Clach Dhian).
In Gleann Einich, traces of the preglacial valley floor can be seen at ~800 m on the floor of Coire Dhondail. The corries have periodically fed ice into the trough but the corries on the SE flank appear to predate trough formation. Coire a' Phocaid, in contrast, seems to have developed since trough deepening but was overwhelmed by ice flowing from the plateau during the Late Devensian and other glacial periods. It is clear that the Gleann Einich trough has had a long and complex history. The Cairngorm troughs have been carved out by successive ice streams and valley glaciers over the last million years or so of the Ice Age.