Surface processes, quantitative geomorphology
Our studies have been directed towards determination of surface erosion rates at various scales (temporal and spatial) and at different climatic conditions, and towards understanding the response of drainage network systems in mountain belts to tectonic forcing and climate change, and to variations in exposed source rock lithologies.
Research on the analysis of possible controls on the evolution of drainage network systems was carried out using numerical models. The model results suggest that a climate change results in a topographic growth or decay of a mountain belt, but not in a modification of the drainage pattern.
Our most recent studies have been directed towards a quantification of surface erosion in the Andes of Chile and Peru, and in the Alps of Switzerland using photogrammetric techniques, low-temperature thermo-chronometers, cosmogenic nuclide analyses and sediment discharge data that is interpreted in terms of sediment yields and erosion rates. These quantitative datasets have been combined with geomorphic and geologic information from the field to interpret possible controls on the calculated patterns of sediment yields. The results imply that the erosional efficiency in watersheds is enhanced if the downslope flux of mass is balanced by sediment transport in channels, It appears, however, that this balance crucially depends on climatic conditions. Indeed, field studies carried out in Northern Chile combined with cosmogenic nuclide analyses imply that a change towards more arid climatic conditions (which appears to be the trend of modern global climate) tends to shift erosional processes to a weathering-limited stage, which, in turn, has promoted fluvial dissection and topographic roughness.
Climate, erosion and tectonics
We interpreted differences between longitudinal stream profiles of the major Alpine rivers in terms of regional variations of erosional potentials. Interestingly, regions with enhanced erosional potentials correspond with areas of anomalously high rates of rock uplift, implying a positive feedback between partitioning of strain and surface erosion. Similarly, our studies imply that the phase of lateral crustal gowth (formation of the Southern Alps and the Jura fold-and-thrust belt) between the Middle and Late Miocene was possibly controlled by a reduction of surface erosion rates at constant rates of crustal accretion. Specifically, sediment budgets from circum-Alpine sedimentary basins indicate a decrease in the erosional efficiency in the Alpine hinterland several million years before lateral orogen growth was initiated, and decreasing magnitudes of sediment discharge thereafter. This decrease in erosional efficiency of the hinterland approximately coincides with widespread exposure of the crystalline core in the Alpine hinterland as indicated by clast types in conglomerates of synorogenic deposits, and with a contemporaneous increase in the continental influence in the palaeoclimate as suggested by the fossiliferous plant record. We suggest that the observed decrease in erosional efficiency caused gravitational forces to increase relative to tectonic forces driving the orogenesis, which led to a transition from dominantly vertical to horizontally directed extrusion.
Basin analysis, tectonics of sedimentary basins
We carry out research in the Swiss Alps and in the Andes of Chile to understand possible links between tectonics, surface erosion, subsidence pattern and stratigraphic architecture. We found that within the foreland basin of the Swiss Alps, the spatial pattern of subsidence and alluvial fan construction suggests that an increase in flexure of the foreland plate and the creation of relief in the orogen migrated from east to west in the course of collision. It appears, therefore, that the westward motion of the Adriatic wedge ultimately caused the contemporaneous westward propagation of the location of enhanced rates of alluvial fan construction. Coeval strike-slip and N-S convergence juxtaposed the Adriatic wedge sequentially to different European upper crustal units which resulted in different styles of crustal structure and evolution along strike within the orogen.
Research group Exogene Geology
