Talus rock glaciers in the Cairngorm Mountains

Although several relict talus rock glaciers (TRGs) of Lateglacial age have been identified in the British Isles, all have been refuted by some authors and their absence attributed to the lack of permafrost. The evidence provided by palaeoclimatic reconstructions and periglacial features, however, implies that Lateglacial permafrost was present throughout Scotland during the Loch Lomond Stade (LLS; ∼12.9–11.7 ka). Across much of the Scottish Highlands, the absence of Lateglacial TRGs is attributable to occupation of potential sites by glaciers during the LLS. In the Cairngorms, however, where limited snowfall at that time left some corries glacier-free, there is convincing evidence for TRG formation. Three examples illustrating different degrees of TRG development are described; all occur at high-level (>840 m) sites that remained glacier-free during the LLS, and all lack plausible alternative explanations. The apparent scarcity of relict TRGs even in the Cairngorms may reflect the development of ‘cold’ permafrost and/or a lengthy time lag between permafrost development and the accumulation of a sufficient volume and thickness of ground ice to permit permafrost creep and deformation of an overlying mantle of bouldery debris. In consequence, relict TRGs may occur only at favourable high-level sites where permafrost developed earliest.