Andean growth and monsoon winds drive landscape evolution at SW margin of South America

- We examine long-term relief evolution and incision processes in the Atacama Desert.
- Using geological constraints as boundary conditions we model landscape evolution.
- The transition from exoreic to endoreic drainage is due to long term N-S rainfall gradient.
- Uniform km-scale tectonic uplift is the driver for river incision in the last ∼10 Myr.
- Trench-ward relief growth incorporated coastal Atacama to the Andes mountain belt.

In the Atacama Desert, the driest place on Earth located at the subduction margin of the Andes, the landscape evolves very slowly and changes in tectonic or erosion processes remain for a long time in the memory of topography. At latitude ∼19°30′S, a threshold between exoreic and endoreic drainage regimes is clearly associated with the latitudinal gradient imposed by the modern monsoon (carrying humidity from the Atlantic) and disposed obliquely over catchments draining the Andes to the Pacific. We summarize the geomorphic, geological and climatic data in the threshold area. We then use these data to constrain numerical experiments of drainage evolution. Data and experimental results are consistent with the development of a flat low-energy morphology, close to sea level, interrupted at ≤10 Ma by tectonic uplift prevailing to the present suggesting trench-ward relief growth by incorporation of the coastal Atacama region to the Andes mountain belt.

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