Channel evolution processes in a diamictic glacier foreland. Implications on downstream sediment supply: case study Pasterze/Austria
Abstract. Global warming and glacier retreat are affecting the morphodynamics of proglacial rivers. In response to changing hydrology, the altered hydraulics will significantly impact future glacifluvial erosion and proglacial channel development. This study analyses a proglacial channel evolution process at the foreland of Austria’s biggest glacier Pasterze, by predicted runoff until 2050 based on a glacio-hydrological model. A high-resolution digital elevation model was created by an unmanned aerial vehicle, sediment was sampled, a one-dimensional hydrodynamic-numerical model was generated, and bedload transport formulas were used to calculate the predicted transport capacity of the proglacial river. Due to the fine sediment composition near the glacier terminus (d50< 79 mm), the calculation results underline the process of headward erosion in the still unaffected, recently deglaciated river section. In contrast, an armor layer is already partly established by the coarse grain size distribution in the already incised river section (d50> 179 mm). Furthermore, already reoccurring exposed non-fluvial grain sizes combined with decreasing flow competence in the long term indicate erosion-resistant pavement layer formation disconnecting the subsurface sediments for glacifluvial reworking (vertical landform decoupling). The presented study shows that subsystems exhibiting pavement layer formation by grains exceeding the predicted transport capacity supported by non-fluvial sediments are found at the investigated glacier foreland. Thus, an extension accompanied by a refinement of the fluvial system in the sediment cascade approach was developed as a central result.
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