Major moraines on the western(left bank)flank of Glen Tromie
Terminal moraines
Definition: End moraines, or terminal moraines mark the end of a glacier; several may run in arcs and mark former positions of a glacier front. They are ridges of till, not usually higher than 20 m. In plan, they often form a series of crescents, corresponding with the lobes of the glacier; a well-developed example indicating that the ice front was at that location for some time. Not all former ice fronts are marked by terminal moraines; some may have been destroyed by meltwater.
Terminal and recessional moraines occur widely in the glens and corries of the Cairngorms and on the surrounding moraines. In many areas, the moraine systems have yet to be mapped in detail, although there are notable exceptions to this:
- corrie and valley head moraines were mapped in the last century as indicators of the extent of ice in the Cairngorms during the Loch Lomond Stadial, the cold stage between 11 and 10 14C years ago. There remain many disputes regarding the extent of ice at this time and its style of build-up and retreat (Sissons, 1979, Sugden, 1980). The moraines themselves tend to be relatively small and formed of large blocks of granite, some transported on top of the former glaciers after falling from cliffs. The most accessible examples are probably the small moraines in Coire an t-Sneachda. The moraine complexes in Garbh Coire, Glen Geusachan and Glen Eidart (Bennet and Glasser, 1991; Bennet, 1996) indicate that the glaciers remained active throughout most, if not all of the retreat phase but latest work suggest that these major moraine systems are the products of ice sheet deglaciation.
- the largest terminal moraines are those associated with the readvance of the Strathspey ice lobe around 15-14 thousand years ago (Brazier et al., 1998). The associated landforms have been mapped on the margin of Glen More from Lochan Eilean to Ryvoan. Strathspey ice initially advanced to an elevation of around 800 m on the flanks of the mountains and then readvanced to successively lower levels. This created a complex of moraines, meltwater channels and landforms of meltwater deposition. Large moraines formed at this time can be seen as benches on the hillsides from Ryvoan, below the ski car park and in lower Gleann Einich. Particularly fine sequences of moraines occur in the valley of the Allt Bheadhair, where local readvances of the ice front have over-ridden glacial lake sedments.
A significant research effort is underway to resolve the timing of these ice margin fluctuations. Members of the British Geological Survey are mapping moraine systems along Strath Spey. A cosmogenic dating programme is underway in the Northern Cairngorms based at the University of Edinburgh. Martin Kirkbride and Doug Benn are busy applying a new dating technique based on the progressive edge rounding of boulders. The value of the technique has already been demonstrated on Lochnagar.