Surface Evolution of Mountains and Drainage Basins under Climatic and Tectonic Forcings

Abstract

The landscape records the interplay between climatic and tectonic events. However, the landscape signals generated by tectonic uplift and climate change often overlap, making it difficult to separate and quantify the contribution of each forcing. Extracting diagnostic signals from the landscape and interpreting climatic and tectonic history remain major challenges. This thesis uses landscape evolution modeling to investigate landscape changes under climatic and tectonic forcing and explore the uplift history of the Altiplano in the Central Andes.

The first part develops a comparative theoretical framework for studying drainage basin responses to changes in rainfall and uplift. Results show that transient changes in headwater channel slope provide an effective diagnostic signal for distinguishing climatic from tectonic forcing. Changes in rainfall rate lead to a transient slope change reversal due to the lag between hillslope and fluvial processes. In contrast, tectonic uplift keeps the slope fixed before the arrival of the erosion wave. Additionally, divide migration is more sensitive to rainfall changes than uplift under orographic rainfall. These contrasting responses provide important indicators of their relative roles.

The second part of the thesis applies the theoretical framework to the Altiplano to investigate its uplift history. By testing five uplift scenarios and three fold setups, the results indicate that fold shortening is important in reproducing the N-S tributary pattern and knickpoint distribution. The landscape generated by the stepwise uplift under horizontal fold shortening is most consistent with the modern landscape.

Overall, this thesis establishes a theoretical framework to decouple climatic from tectonic forcing. It also shows how the framework can be applied to a natural system to constrain its uplift history. Additionally, it demonstrates that modern landscapes can be linked to the climatic and tectonic processes that shaped them.