Research published in Science early in 2008 suggested that the rivers in most of the eastern United States owe their morphology and ongoing processes to the construction of mill dams following European settlement, and their recent demise around the middle of the twentieth century. This idea was very controversial because huge expenditures for stream restoration and watershed management are based on the idea that streams of the region are equilibrium-meandering channels adjusted to a constant bankfull discharge. Pizzuto and Neal test one aspect of the controversial hypothesis at a field site in Virginia: that current bank erosion rates have increased in recent decades, due to the demise of mill dams. Using historical aerial photographs, they document an increase in river bank erosion rates after 1957, and find that the demise of mill dams along the river around the same time provides the best explanation for their observations.
Surface cracks record long-term seismic segmentation of the Andean margin
John P. Loveless et al., Department of Earth and Atmospheric Sciences, Cornell University, Snee Hall, Ithaca, New York 14853, USA. Pages 23-26.
Knowledge of the location and size of past earthquakes along the world's subduction zones can aid in assessing future seismic hazard. However, geologic evidence documenting the effects of historical earthquakes often exists only for the past several events, limiting our ability to recognize truly long-lived patterns of seismicity. Here Loveless et al. demonstrate that in the arid Atacama Desert, Chile, meter-scale surface cracks that open in response to large earthquakes preserve a record of the locations and extent of earthquakes over the past several hundred thousand years. They used high-resolution satellite imagery from Google Earth to map over 50,000 of these features in coastal regions of northern Chile and souther
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Geological Society of America