Debris at the edge: sedimentological dynamics of Hintereisferner's evolving terminus and glacial forefield, Austrian Alps

Abstract

The interaction between glaciers and the debris accumulating on their surfaces is critical as the Earth warms, with consequences for ice dynamics, hydrology and mass balance together with slope and sedimentary processes. Understanding this interaction is necessary since it influences ablation rates, sediment and meltwater pathways. The Hintereisferner glacier (Austrian Alps) has over a century's worth of observations and while mostly a clean and debris-free glacier, the last kilometre is becoming covered by debris. In this study, we present new geomorphological and sedimentological work, including glacier debris and forefield mapping that sheds light on the temporal and spatial accumulation of debris. The characterization of the forefield and terminus of the Hintereisferner permits identification of sediments and landforms, which were classified into landsystems. The subglacial/glaciofluvial dominated forefield has been exposed in the past 25 years, uncovering sections that demonstrate shifting channels with oscillating energy conditions in contact with till. The supraglacial landsystem consists of ablation cones and transverse ridges (both with low preservation potential), associated with crevasse infill by meltwater and englacial debris emergence, respectively. Additionally, the supraglacial system includes debris cover units with a paraglacial component that correspond to debris derived from both gravitational processes and heavy precipitation events, modifying the supraglacial meltwater system. It is expected that debris flows will be the main contributor of debris onto the glacier surface, that cauldron structures will continue to develop and eventually collapse, and most landforms will not be preserved as the forefield evolves. A coupled understanding of the recent deglacial landscape, together with the processes of debris accumulation on the glacier margin requires a rigorous mapping approach, which should be widely applicable to other mountain glaciated terrains.