Collaborative Research: Rivers, Faults, and Growing Mountains: Dynamic Feedback between Crustal Deformation, Rock Strength, and Erosion

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The topography of most active mountain ranges shows a clear link between deformation and erosion in the form of valley networks that align closely with faults and shear zones. We propose that this association is the signature of dynamic feedback between deformation, rock damage, and surface erosion, and that this feedback plays a fundamental role in the evolution of orogens. With this research program, we will test our hypothesis that the rock crushing associated with tectonically-driven earthquakes reduces the strength and grain size of the upper crust of the Earth, producing zones at the surface of material that is more readily eroded by rivers, landslides and glaciers. Erosion along these weakened fault zones proceeds more rapidly than the non-deformed material, and consequently, the deformation history is recorded within the topographic fabric. The 3D orientation of these fault-weakened zones is largely determined by large scale plate tectonics related to mantle convection. Consequently, if our hypothesis is sustained, then we will be able to use the orientation of surface features (valleys and ridges) to describe the long term history of mantle convection at relatively high resolution.To test this hypothesis, we propose a program that combines advanced numerical modeling and field data collection in the Southern Alps of New Zealand to evaluate two testable predictions: (1) that there should exist a correlation between topography and rock strength, as reflected in properties such as bulk cohesion, fracture density, friction coefficient, tensile strength and grain size; and (2) that a coupled model of 3D deformation and erosion, based on our current understanding of the relevant physics, should produce patterns of topography, erosion, and strain that are both consistent with observations and substantially different from the case of uniform rock strength. We anticipate that this research will provide critical information for scientists working on the interdependence of surface and tectonic processes at scales ranging from those of mantle convection to those of individual drainage basins. As part of the outreach associated with this program, we will produce and test a Web-accessible landscape modeling module that will permit numerical experimentation by k12 and general audiences of landscape development in a simplified, coupled geomorphic/tectonic orogenic system.This project is supported by the Geomorphology and Land-use Dynamics program and the Tectonics program. In addition, this award is designated as an OIIA/ISE Global Venture Fund Award and is being co-funded by NSF's OIIA International Science and Engineering Section.