Short-Term Spatial and Temporal Patterns of Glacio-Fluvial Sedimentation at Feegletscher, Swiss Alps

Abstract

Analysis of short-term spatial and temporal patterns of glacio-fluvial sedimentation associated with recent glacier retreat at Feegletscher, Swiss Alps, was undertaken. Data was collected through glacial imagery, ablation, meteorological, and proglacial channel monitoring to understand how sediment transport in a glaciated catchment with two geomorphologically contrasting proglacial zones functions during, and is responding to, recent glacier retreat. The research was performed during the 2019 ablation season on the Feegletscher Süd and Feegletscher Nord, Switzerland, whose proglacial streams are situated in geomorphologically contrasting proglacial zones. To the best of this investigation's knowledge, this is the first study to identify short-term intra-basin spatial and temporal patterns of glacio-fluvial sedimentation of two geomorphologically contrasting proglacial zones. The Feegletscher Nord's upper proglacial area is characterised by a narrow gorge and a waterfall that leads into a braided proglacial source of unstable, unconsolidated fine glacio-fluvial sediment deposits, and the lower proglacial area displayed consolidated morainic sediment deposits and reworked paraglacial debris. The Feegletscher Süd's upper proglacial area is characterised by a clean bedrock forefield with minimal quantities of glacio-fluvial sediment deposits, followed by a proglacial channel that is constrained by incised lateral moraines. Examples of data analysis techniques that were used are the cross correlation of meteorological and proglacial channel data to determine links between all variables, and hysteresis plots of suspended sediment concentration-discharge to indicate glacio-fluvial dynamics. This research showed that there was variability in fluvio-glacial sedimentation between the multiple monitoring stations along the Feegletscher Nord's proglacial stream, and between the Feegletscher Nord's and Süd's proglacial stream. Both clockwise and anti-clockwise hysteresis was observed at all monitoring sites. The Feegletscher Süd showed an overall clockwise hysteresis, the upper monitoring site on the Feegletscher Nord showed anti-clockwise hysteresis, and the lower monitoring site on the Feegletscher Nord showed equal amounts of clockwise and anti-clockwise. The variability in hysteresis between the monitoring stations is attributed to sediment exhaustion, and the overall availability and stability of fine grained sediment within each proglacial area, which is controlled by variations in sedimentary and geomorphological characteristics. The differences in glacio-fluvial sedimentation at Feegletscher demonstrate that even within a relatively small glaciated catchment a range of spatial and temporal patterns exist, and a major control on determining these patterns is the location and quantity of the monitoring stations within the proglacial forefield. The additional complexity of comparing geomorphologically contrasting proglacial zones showed the importance of considering the geomorphological history of the proglacial zone when identifying the location and quantity of monitoring stations. The short-term spatial and temporal patterns of glacio-fluvial sedimentation and variability between each monitoring station demonstrated that long-term fully integrated studies are required to get a full understanding of glacio-fluvial sedimentation. A fully integrated catchment-wide study that integrated meteorological inputs to the catchment, as well as inflow, through-flow, and outflow of glacier meltwater and sediment would enable the ability to fully extrapolate suspended sediment concentrations and fluxes, sediment transportation mechanism, and to acquire a full understanding of the impacts caused by future glacier retreat.