Agricultural Vs. Geological Erosion Rates in Arid Environments: A Case-Study in Southern Peru

Erosion studies on natural and agricultural settings at various scales (plot, hillslope, catchments) employing laboratory experiments, sediment traps, soil profile truncation and cosmogenic nuclide to calculate rates find widely divergent erosion rates even under similar conditions of climate and soil. The research reported here uses undisturbed archaeological sites abandoned in 1000 A.D. and 1532 A.D in arid Southern Peru environments to observe patterns and rates of geomorphic change on constructed slope. The agricultural erosion rates, 94 m/my to 120 m/my determined from these archaeological sites are substantially greater than the erosion rates calculated using cosmogenic nuclides.

Short duration and high intensity rainfall at the study sites concentrates erosion at the edge of the terrace risers, leading to rilling of the tread surfaces. Some of the sediment derived from erosion of both terrace risers and treads is redistributed downslope within the terraces, while the rest of the sediment is completely removed from them. Erosion on these archeological earthworks is more than thirty times faster than reported on natural slopes in nearby areas.