Thematic mapping for sediment cascade analysis in small mountain catchments – The case of the Buscagna valley (Lepontine Alps)

Abstract

The multi-scalarity of mountain systems primarily relates to their complex structural settings, which lead to the fragmentation of geological and geomorphological units. This may have strong implications for the hydrogeomorphological evolution of watersheds and the related sediment cascades. In the framework of this research, we selected the small Buscagna mountain catchment in the Lepontine Alps (Northwestern Italy), where the northern slope comprises very resistant gneissic rocks, while soluble rocks (i.e., marble) – in some case intensely foliated (i.e., calcschist) –crop out along the southern slope. The diversification of geomorphological processes and landforms (i.e., geomorphodiversity) is highly evident, and various techniques are applied to create thematic maps of geomorphological features (landforms; processes; erosion/deposition/deformation), sediment connectivity, and source/store/sink distribution in the Buscagna catchment. The obtained thematic maps were integrated and compared to depict the influence of bedrock features on geomorphological evolution. The geomorphological maps focussed on landforms and processes reveal that glacial and gravity-related processes and permafrost distribution are deeply influenced by the topographic and lithological dichotomy of the catchment. Permafrost distribution is again uneven in the basin, and its degradation allows relevant sediment sources to be delivered downstream. Lastly, debris flows represent the primary connectivity triggers between areas such as the hanging glacial basin slopes and the valley bottom (i.e., erosion/deposition/deformation and index of connectivity maps). What emerges is the importance of integrating and comparing different thematic maps for a correct interpretation of the past and present dynamics influencing the evolution of complex, albeit small, mountain catchments.