Quantitative determination of long-term erosion rates of weathered granitic soil surfaces in western Abukuma, Japan using cosmogenic 10Be and 26Al depth profile

Abstract

We present erosion rates of granitic soil surfaces in the western Abukuma upland, Japan using depth profiles of in-situ produced cosmogenic 10Be and 26Al based on physical parameters for both neutron and muon interactions. Samples were obtained below the severely weathered zone, from 30 to 190 cm depth below surface (bs). We confirmed that, in this environment, deeper layers from at least 80 cm bs must be analyzed to achieve highly accurate measurement of erosion rate because near-surface layers are potentially influenced by pedogenic processes. The depth profiles obtained suggest a surface-lowering rate of 49-74 m/Myr for a mountain ridge composed of granitic soil. This newly obtained erosion rate is much higher than previously reported granitic or metamorphic bedrock, as well as quartz vein, erosion rates from several climatic environments including humid regions, suggesting that granitic soil surface is more susceptible to erosion. © 2010, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.