![]() ![]() Historically, discharge and sediment concentration measured at a distance downstream from glaciers served as a proxy to assess glacial erosion response as well as interactions between subglacial hydrology and sediment dynamics. Each of these geomorphic domains is defined by its position relative to the glacier and exhibits distinct geomorphic processes. Importantly, the sediment signal from a glaciated catchment integrates processes of transport and production over three distinct geomorphic domains: (i) the supraglacial rockwalls, (ii) the ice-covered subglacial substratum, and (iii) the glacier forefront. Similarly, there is ample evidence of ongoing paraglacial adjustment linked to more recent glacial retreat with examples from Svalbard, Iceland, the French Alps, the Swiss Alps, the Austrian Alps, the Himalayas, Alaska, and British Columbia. For example, the paraglacial response to the last glacial maximum led to a significant increase in sediment discharge in the Alps, in British Columbia, in the Cascade Range and in the Teton Range. Conceptually, sediment is produced during cool, dry glaciation periods and exported during warmer, wetter inter-glacial periods. Formally, “paraglacial” refers to processes and landforms conditioned by the antecedent presence of a glacier. Sediment export from glaciated catchments is best described by the paraglacial concept: a source-to-sink approach linking sediment export to climatic conditions inducing varying ice-coverage. Sediment export from glaciated catchments is pivotal: it is likely to increase, modulates flood risk and reservoir sedimentation, impacts river management, and possibly inputs large amount of sediment to downstream systems. In that context, water and sediment flux in glaciated watersheds will display significant change. Observed and projected change to the headwaters of mountain watersheds leads to complex perturbations of their hydrologic regime and downstream ecosystems. Ice volume and glaciated surface area have drastically reduced during the 20th century, and projections indicate further decline during the 21st century. To conclude, the present-day sediment response in Bossons catchment displays distinct components with characteristic timescales and is dampened by intermediate storage controlled by drainage development and extreme events in the glacial and proglacial domains. In addition, glacial retreat in link with higher melt rate allows for exporting a pluri-annual sediment stock stored beneath the glacier. The evolution of the drainage network throughout the melt season explains the evacuation of the annual and pluri-annual subglacial sediment stocks. ![]() In addition, three years exhibit late melt season exports which are uncorrelated with temperature or rainfall. In the Bossons stream catchment, the sediment response highlights the initiation of the dendritic drainage network beneath the glacier, the short-lived evacuation of an annual storage during the early melt-season and its subsequent steadier regime. High resolution hydro-sedimentary flux data were acquired during eight years in two proglacial streams with contrasting glacio-hydrological characteristics, Bossons and Crosette streams. This study nuances these observations by quantifying the contribution from each geomorphic domain to the export of a glaciated catchment in the North face of Mont-Blanc (France). The dominant process controlling present-day sediment export from glaciated catchments remains debated with most studies underlining the paraglacial dynamics in the glacier forefront. The detrital export from such environments results from erosion processes operating in three geomorphic domains: the supraglacial rockwalls, the ice-covered substratum and the proglacial area, downstream from the glacier. Present-day global warming raises important issues regarding sediment flux from glaciated catchments. ![]()
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