Late Holocene debris cone evolution in Glen Feshie, western Cairngorm Mountains, Scotland

Abstract

ABSTRACTRecent river erosion of three coalescing debris cones in Glen Feshie has exposed a complex sequence of debris flow units. Radiocarbon dating of organic matter from interbedded buried soils reveals that the soil at the base of the sequence was buried atc.2000 yr BP, but that the bulk of the cones accumulated since the fifteenth century AD. The episodic nature of cone development is attributable to lateral migration of the River Feshie, with periods of cone accumulation when the river occupied the far side of its floodplain alternating with periods of erosion when the river impinged on the cones. There is no evidence to suggest that recent cone accumulation is related to anthropogenic vegetation disturbance, but phases of cone accumulation show a broad temporal correspondence with periods of Late Holocene climatic deterioration. The cones are essentially paraglacial in that their continuing accumulation depends on a supply of sediment derived from glacial and periglacial deposits upslope. The form of debris-flow units indicates that flows at this site were less viscous than most ‘hillslope’ flows, and cone volumes indicate an average annual accumulation ofc.50–60 m3of sediment over the pastc.300years.