Jay Quade et al., Dept. of Geosciences, University of Arizona, Tucson, Arizona 85721, USA. Posted online 18 July 2012; doi: 10.1130/G33162.1.
Jay Quade and colleagues discovered clusters of more than one ton-sized boulders in the Atacama Desert of northern Chile worn to smoothness around their mid-sections. They suggest that the boulder smoothing is the cumulative result of at least a million years of rubbing between boulders during earthquakes. Dating of the boulder surfaces shows that they have been exposed for greater than a million years. During the research team's second field visit to one major boulder site, they experienced an earthquake that rocked but did not tip the boulders, causing them to rub against each other for about a minute. This 5.6 magnitude earthquake was centered about 100 kilometers northeast of the site. In the seismically active Atacama, earthquakes of this energy or greater occur about once every four months, suggesting that the average boulder has experienced ~40-70 kilohours of abrasion over the past 1.3 million years. This unusual evidence underscores the largely unrecognized role that seismicity probably plays in hillslope sediment transport in the nearly rainless Atacama Desert and perhaps on other seismically active but now dry worlds like Mars.
Glacier expansion in southern Patagonia throughout the Antarctic cold reversal
Juan L. Garca et al., Instituto de Geografa, Facultad de Historia, Geografa y Ciencia Poltica, Pontificia Universidad Catlica de Chile, Campus San Joaqun, Avenida Vicua Mackenna 4860, comuna Macul, Santiago 782-0436, Chile. Posted online 23 July 2012; doi: 10.1130/G33164.1.
Juan L. Garca and colleagues built a glacial chronology based on Beryllium-10 cosmogenic exposure dating of boulders resting on moraines in Torres del Paine National Park, Chile (51 degrees S, 72 degrees W). Recent improvements of geochro
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