Rockfall talus slopes and associated talus-foot features in the glaciated uplands of Great Britain and Ireland: periglacial, paraglacial or composite landforms?

Abstract

AbstractThe traditional interpretation of talus slopes and talus-foot landforms in the glaciated uplands of Great Britain and Ireland has been that they are periglacial landforms associated with freeze–thaw activity and permafrost. Since about 1990 some reassessment of this widely held view has occurred, and paraglacial rockfall and rock-slope failure are now considered to have played a significant role in the development of some talus landforms; in certain cases a wholly paraglacial origin is advocated. In order to determine formative processes, critical site-specific evidence (morphological and sedimentological) needs to be obtained. This will enable models of the deglacial–post-glacial evolution of these landscapes to be proposed and allow the palaeoenvironmental significance of the landforms to be established. Distinguishing between a periglacial and paraglacial origin might be assisted by application of cosmogenic isotope surface-exposure dating, which may demonstrate a Holocene age for a particular landform and thus rule out a permafrost-related origin. However, there will be instances where the application of dating will not differentiate, as in the case of Late Glacial landforms that could be either periglacial or paraglacial. It is likely that equifinality applies with respect to these landforms and a composite origin for them should also be considered. This latter issue is one that has not previously been given much consideration, probably because of the inherent difficulties in recognizing the products of different processes in landforms for which exposures of their constituent materials are rare.