Rock varnish is a thin dark coating best known from deserts, and is believed to grow extremely slowly. Varnish samples from near Socorro, New Mexico (United States), contain as much as 3.7% lead oxide, derived from nearby smelters operating from A.D. 1870 to 1931. Additional varnish indicates continued growth from 1931 to 2003. Comparison with other varnish confirms that the lead is not an artifact. Based on Pb layer thickness, and the period of smelter operation, these very young rock varnishes yield growth rates of 28 to 639 microns per thousand year, substantially higher than previously documented fastest rates. These rates imply that the average rate for older varnish is not the active growth rate. Rather, it is a long-term value including periods of nondeposition, erosion, and active growth. Therefore, models of rock varnish formation should be reevaluated with consideration of much faster maximum growth rates.
Construction of an oceanic island: Insights from the El Hierro (Canary Islands) 2011-2012 submarine volcanic eruption
J. Rivera et al. (M. Canals, corresponding), Instituto Espaol de Oceanografa, Corazn de Mara 8, Madrid E-28002, Spain. Posted online 4 Jan. 2013; http://dx.doi.org/10.1130/G33863.1.
J. Rivera and colleagues present the first continuous monitoring of the growth of a newly born submarine volcano while erupting in an ocean island flank. The eruption occurred south of El Hierro Island in the Canaries, off Northwest Africa, from 10 October 2011 to 5 March 2012 and was marked by earth tremors, stained waters, and dead fish. An unprecedented high-frequency, high-resolution bathymetric monitoring allowed calculating changes in eruption rates. The first survey, 15 days after the eruption's onset, showed a cone topping at 205 m depth. 137 days later, the cone had developed into a fi
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Geological Society of America