Post-Glacial Modifications to the Cairngorms Landscape

Sep 2, 2010
Jennifer Young

: Blocky weathered granite, Cairngorm summit - Jennifer Young

Scotland's Cairngorm mountains are a bleak plateau carved by ice in the last ice age. Many erosive processes continue to modify the landscape.

The bleak, high, granite massif of the Cairngorm mountains in the Scottish Highlands contains some of the country’s highest peaks. Though its current shape has been largely determined by geology and by the action of a succession of glaciers, the landscape continues to be modified by a series of ongoing erosive processes.

Glacial Action at the End of the Ice Age

Radiocarbon dating indicates that the main body of ice had disappeared from the Cairngorms by around 13,000 years ago, though a later readvance (known as the Younger Dryas, or the Loch Lomond readvance) occurred around 2,000 years later. This second pulse of ice was heaviest in the west, where it created significant changes including formation of glacial lakes, meltwater channels and fossilised lake shores such as the Parallel Roads of Glen Roy (McKirdy et al).

In the Cairngorms, glacial activity during the readvance was restricted and, apart from the deposition of some new morainic deposits, intensive periglacial activity (frost action) took place, generating the ‘blocky’ landscape of heavily weathered granite which can be seen at the top of the Cairngorm plateau (McKirdy et al, British Geological Survey).

Modification of the Landscape: Erosion

After the ice had retreated, large quantities of glacial deposits remained and these were – and continue to be - eroded by rivers, which carried huge quantities of material down from the mountains, depositing them in the flatter areas as the water lost energy. This combination of processes is responsible for the typical scenery of rivers meandering along glaciated valleys – for example, the upper reaches of the river Dee.

The abundance of loose weathered material left by the glaciers and by the intensive periglacial processes meant that many of the slopes were, and continue to be, unstable and easily undermined by rivers, by weight of snow or by saturation. Recent slope and river bank collapses can still be seen, as can fresh deposits of the material revealed by slope failure.

Modification of the Landscape: Weathering

Weathering is significant in the Cairngorm landscape. Although the glaciers have long gone, the height and latitude of the Cairngorms continues to sustain a subglacial landscape. Temperatures are low, with many days of heavy frost each year: the information board at Cairngorm summit indicates that the average monthly temperature is above freezing only between June and October, while the minimum temperature is below freezing all year.

Rain dissolves the minerals in the granite and freezes and refreezes in cracks in the rock. Regular hard frosts create tensions within the rocks, leaving sharp-edged fragments which are washed down the slopes by rivers, blown by the high winds, or which creep downslope under gravitational forces to create scree.

The Cairngorms: Landscape Character

The Cairngorms' harsh climate and complex geological history has generated a unique habitat for animals, birds and plants. On the granite tops vegetation is sparse, frail and often absent, while lower down the thin soils support mainly pine woodland. The value of geology and landscape are recognised and protected, and the Cairngorms are now a National Park.