Formation, morphology, and retreat of autogenic waterfalls

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Earth’s topography is sculpted by both the movement of tectonic plates (which build topography) and climate (which erodes topography). As such, changes in climate or tectonics can be recorded in subtle topographic variations. For example, where tectonic faults cross rivers, changes in fault movement can lead to waterfall formation. These waterfalls can remain in landscapes for thousands to millions of years, allowing geologists to use the presence and position of waterfalls to infer past changes in Earth history. However, recent work has suggested that waterfalls may also spontaneously self-form, even when climate and tectonic forcing remains constant. Therefore, using waterfalls to ‘read’ Earth history from landscapes requires distinguishing self-formed waterfalls from those that form following changes in climate or tectonics. This project seeks to distinguish such waterfalls, thereby fundamentally improving our ability to decipher past changes in Earth history. Beyond this scientific advance, the project will promote public interest in the Earth sciences via harnessing the awe of waterfalls to engage in community outreach through the creation of online videos and K12 classroom visits focused on mountain stream hazards and waterfall formation. The project will also support the PhD and masters project of two female early-career scientists, as well as provide training for undergraduate students. The goal of this project is to investigate the mechanisms by which waterfalls can self-form (or form autogenically), as well as the morphology and erosion rates of self-formed waterfalls. This will be accomplished through a mix of laboratory experiments, field work, and modeling. Laboratory flume experiments will test the conditions under which autogenic waterfalls form, and these results will be compared to existing theory for the development of bedrock steps as well as a large database of putative autogenic waterfalls that will be collected as part of the project. The lab and field work will allow development of quantitative, non-dimensional metrics to identify autogenic waterfalls in the field, and will allow assessment of the ubiquity of autogenic waterfalls in nature. Finally, these results will be applied to develop a river long profile evolution model that accounts for autogenic waterfall formation and retreat, and can be used to predict the coupled response of landscapes to autogenic dynamics and external perturbations. This project thus fills a fundamental knowledge gap on how autogenic processes modify bedrock landscapes, thereby enhancing our ability to ‘read’ the record of Earth history recorded in topography.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.