Collaborative Research: Uplift or climate change? Determining the primary driver of deep canyon incision in the eastern cordillera, southern Peru

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Competition between the growth of new topography by tectonic uplift and erosion that wears it down occurs in many mountain regions. Earth scientists recognize that the ability of rivers to erode depends on how much water is delivered to the mountains, and that changes between wetter or dryer climates should influence topography. The expectation is that changes in climate and the resulting change in erosion are reflected in the topography of a landscape. This project focuses on the Eastern Cordillera of southern Peru, where deep canyons carved into the Central Andean Plateau margin reflect either tectonic uplift or an increase in erosional efficiency due to climate change. The research incorporates newly-developed methods for diagnosing the effects of climate on topography as part of a field-based investigation to determine the degree to which climate-driven changes in erosional efficiency are responsible for canyon cutting. New remote analysis methods are used to differentiate signatures of tectonic uplift driven erosion and climate driven erosion in topography. Improving the fidelity of these remote methods has considerable societal value because they are an inexpensive and efficient means of hazard assessment in areas where the presence or absence of tectonic uplift, and the resulting effect on seismicity, are uncertain. Additionally, this project wll benefit society by: 1) essential STEM training of three US graduate students including two women, as well as several Peruvian undergraduates; 2) international collaborations with both Peruvian and German universities; and 3) improved STEM education development in Peru and US at the undergraduate, graduate, and professional levels.Determination of an active tectonic driver of mountain uplift and the geometry of related structures is critical to resolving how strongly climate and tectonics are coupled. This project tests competing hypotheses for the proximal drivers of canyon cutting into the Eastern Cordillera: incision driven by active rock uplift vs. incision into a previously uplifted plateau margin triggered by climate change. Integration of observations and analyses of the deformation history, landscape morphology, precipitation patterns, and spatial and temporal patterns of erosion and exhumation is used to definitively and quantitatively evaluate the relative importance of active rock uplift and climate change in landscape evolution. Analyses focus on: 1. estimating millennial-scale erosion rates from cosmogenic 10Be concentrations in modern river sands, 2. assessing the role of rainfall in the relation between topography and erosion rate, 3. analyzing cooling ages of low-temperature thermochronometers (AHe, AFT, ZHe) provided by a complementary study, 4. refining geologic mapping and developing balanced cross sections, and 5. integrating all data in models to quantitatively test hypotheses. Results will have broad implications for: 1. the general applicability and fidelity of proposed methods for diagnosing the primary causes of canyon cutting based on analysis of geomorphic data, 2. further development of a methodology to quantitatively link geometry, displacement and rates on faults to exhumation rates, erosion rate patterns and the resulting landscape morphology, 3. quantitative, observation-based understanding of the sensitivity of erosion rates to annual rainfall, and 4. understanding of the nature and strength of linkages among climate, topography, erosion, and tectonics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.