Measuring erosion rates on exposed limestone residuum using erosion pins: a 10-year record.

Erosion rates in residual limestone soils in a humid climate were measured for 10 years at one site, and for 4 years at another site, using erosion pins. Erosion pins were placed in gully floors and on convex divides between adjacent gullies, on abandoned land where vegetation had been removed. We measured an average erosion rate of 20 mm yr−1over 10 years at one site and only 5 mm yr−1over 4 years at another site where chert gravel was common on the surface. The 10-year average erosion rate of divides (26 mm yr−1) was significantly greater than the average erosion rate of gullies (14 mm yr−1), suggesting control by different processes, some of which may be seasonal. In winter, it was observed that frost action produced a thin layer of loose soil on the surface of divides. In summer, a hardpan developed on divides, as the soil loosened by winter frosts was transported to gullies, likely by rainsplash or dry ravel. The diffusive processes of frost action, rainsplash, and dry ravel appear to shape the convex divides in this study. Down-cutting of gullies requires channelized flow produced by intense rainfall, which is more common in summer for this location. [ABSTRACT FROM AUTHOR]