Micro-scale topographic controls on functional hillslope-to-stream connectivity in rapidly deglaciating terrain

Abstract

Rapid retreat of Alpine glaciers since the end of the Little Ice Age has increased the spatial extent of proglacial margins. Whilst the response of glaciers to climate warming is well-documented, the response of proglacial landscapes, especially regarding sediment transfer processes, is less understood. Sediment transport, through erosion and deposition, modifies the landscape and affects sediment connectivity. The latter may be described as structural (static, related to the configuration of the system) or functional (dynamic, resulting from time-space variation in sediment flux). This paper quantifies the functional connectivity of sediment flux for a recently deglaciated Alpine hillslope. Analysis of high-resolution digital elevation models is coupled to a morphological method to assesses the spatial pattern of sediment flux required to conserve mass over a seasonal and a multi-year time-scale. Results show that functional connectivity is strongly controlled by micro-scale topography on the hillslope that has developed during and since deglaciation. Functional connectivity is then a key factor determining the delivery of sediment to the valley bottom for eventual transport by the proglacial stream following glacier retreat. This effect is stronger at the seasonal time-scale than at the multi-year time-scale.