As Glaciers Recede, Soils Emerge: Modelling the Dynamics of Proglacial Soil Formation 

Proglacial areas offer valuable insights into soil development in alpine environments and as glaciers retreat due to climate warming, new bedrock is exposed, initiating soil formation. Proglacial areas are dynamic, with soil development influenced by various factors such as glacial retreat, erosion, topographic conditions and geomorphic processes. Understanding these processes is crucial for predicting how soils in alpine landscapes will evolve in response to ongoing climatic changes. Until now, however, our understanding of soil formation processes has been based primarily on point-specific data from samples collected in glacial forefields. To gain a more comprehensive understanding of these processes, we aimed to simulate them across an entire area. Therefore, we developed a new version of an existing soil and landscape model with the objective of enhancing our understanding of soil formation in proglacial areas by simulating the soil development for each pixel of a digital elevation model.The soil and landscape model LORICA integrates geomorphic and soil-forming processes, enabling a deeper understanding of the spatial and temporal aspects of soil development. In high-alpine regions, geomorphic processes, like water erosion, play a critical role in shaping the landscape and influencing soil formation. To apply LORICA to proglacial areas, a "proglacial mode" was developed using the Bachfallenferner study site in Tyrol, Austria. Existing and self-collected soil samples were analysed to obtain information for the model inputs, like the average grain size distributions. The proglacial mode entails some adjustments to model parameters and incorporates an age raster. The age raster reflects glacial extents since the Little Ice Age, allowing simulations of soil development over selected time periods as the glacier retreats and the proglacial area expands. As a result, during a model run, more and more soil is exposed as consequence of the glacial melting and soil formation begins, reflecting reality. In the proglacial mode, the geomorphic process “water erosion and deposition” and the soil forming processes “physical weathering”, “chemical weathering”, “clay dynamics” and “carbon cylcle” are selected as relevant and the parameters for these processes were adjusted to fit the framework conditions of a glacier forefield. In addition, the proglacial mode accounts for the influence of glacier-derived meltwater on the newly forming soils.  The model, including the proglacial mode, was calibrated using representative soil samples from Bachfallenferner. These field-collected data form the foundation for ensuring the model's accuracy and reliability. By complementing traditional soil-sampling methods, our approach provides a comprehensive, area-covering view of soil development in a dynamic alpine environment and represents the first mechanistic model that can depict the successive development of soil in a glacier forefield.