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Hillslopes Record the Growth and Decay of Landscapes

Science  23 Aug 2013:
Vol. 341, Issue 6148, pp. 868-871
DOI: 10.1126/science.1241791

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Gotta Get Up to Get Down

By examining high-resolution satellite topography data of a ridge along the San Andreas Fault in California, Hurst et al. (p. 868) demonstrate how hill slope curvature may be used to infer long-term rates of tectonic uplift and erosion. Numerical modeling shows a lag phase between uplift events and changes in morphology, which, combined with the observational data, shows that topography can reveal whether landscapes are active or decaying. These fundamental relationships may help to improve seismic hazard forecasts or to interpret topographic data collected on other terrestrial planets.

Abstract

Earth's surface archives the combined history of tectonics and erosion, which tend to roughen landscapes, and sediment transport and deposition, which smooth them. We analyzed hillslope morphology in the tectonically active Dragon’s Back Pressure Ridge in California, United States, to assess whether tectonic uplift history can be reconstructed using measurable attributes of hillslope features within landscapes. Hilltop curvature and hillslope relief mirror measured rates of vertical displacement caused by tectonic forcing, and their relationships are consistent with those expected when idealizing hillslope transport as a nonlinear diffusion process. Hilltop curvature lags behind relief in its response to changing erosion rates, allowing growing landscapes to be distinguished from decaying landscapes. Numerical modeling demonstrates that hillslope morphology may be used to infer changes in tectonic rates.

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