Holocene reworking of drift-mantled hillslopes in the Scottish Highlands

Episodic erosion and resedimentation of valley-side glacigenic drift is evident at three sites in the Scottish Highlands in the form of buried in situ palaeosols intercalated with stacked sediment units. Radiocarbon dating of 10 palaeosols exposed in sections in debris cones suggests that gully erosion and redeposition of drift represents asynchronous debris flow and slopewash activity within the past 6⋅5 cal.kyr. Palynological and charcoal analyses confirm that reworking was unrelated to burning of vegetation, and post-dated the main phase of anthropogenic woodland clearance at two sites, although the possibility that recent debris flow activity in Glen Docherty may have been associated with removal of woodland cover cannot be dismissed. However, the collective evidence points to discrete, extreme storm-generated events of random occurrence as the most likely cause of episodes of enhanced slope reworking at the sites investigated. Evidence for periodic climatic deterioration is more equivocal. By implication, the accumulation of substantial debris cones in upland Britain may reflect primarily the reworking of sediment during extremely rare, intense rainstorms, essentially independent of progressive climate changes. Consequently, caution is necessary in using debris flow stratigraphies alone as a means of reconstructing former long-term climatic changes.