Spatiotemporal analysis of channel wall erosion in ephemeral torrents using tree roots—An example from the Patagonian Andes

Abstract

This paper presents absolute ages for fl ash fl oods and related sediment entrainment in headwater catchments to construct a spatiotemporal framework of process dynamics and locations of major areas of channel wall erosion. The most reliable method for dating erosion is through dendrogeomorphic studies of exposed tree roots. Based on the analysis of erosion signals in root-ring records we documented a time series of channel wall erosion and successfully dated 21 erosive fl ash fl ood events since A.D. 1870 in an ephemeral gully in the Patagonian Andes. The study was performed with roots from Austrocedrus chilensis, Nothofagus dombeyi, and Pseudotsuga menziesii. Results demonstrate the potential of root analyses for the determination of major areas of sediment entrainment. In addition, we show that the position of damage within individual root rings allows inferences about the seasonal timing of fl ash fl ood effects and thus an assessment of possible meteorological triggers of erosive events, short intense storms occurring primarily in austral fall and late winter in this case. The approach presented adds signifi cantly to the documentation of sediment entrainment and facilitates identifi cation of areas of rapid erosion in small, remote headwater catchments with ephemeral fl ash fl ood activity.