Articles | Volume 4, issue 1
Research article
02 Feb 2016
Research article |  | 02 Feb 2016

On the potential for regolith control of fluvial terrace formation in semi-arid escarpments

K. P. Norton, F. Schlunegger, and C. Litty

Abstract. Cut–fill terraces occur throughout the western Andes, where they have been associated with pluvial episodes on the Altiplano. The mechanism relating increased rainfall to sedimentation is, however, not well understood. Here, we apply a hillslope sediment model and reported cosmogenic nuclide concentrations in terraces to examine terrace formation in semi-arid escarpment environments. We focus on the Pisco river system in western Peru in order to determine probable hillslope processes and sediment transport conditions during phases of terrace formation. Specifically, we model steady-state and transient hillslope responses to increased precipitation rates. The measured terrace distribution and sediment agree with the transient predictions, suggesting strong climatic control on the cut–fill sequences in western Peru primarily through large variations in sediment load. Our model suggests that the ultimate control for these terraces is the availability of sediment on the hillslopes, with hillslope stripping supplying large sediment loads early in wet periods. At the Pisco river, this is manifest as an approximately 4-fold increase in erosion rates during pluvial periods. We suggest that this mechanism may also control terrace occurrence other semi-arid escarpment settings.

Short summary
Cut-fill terraces are common landforms throughout the world. Their distribution both in space and time is not clear-cut, as they can arise from numerous processes. We apply a climate-dependent regolith production algorithm to determine potential sediment loads during climate shifts. When combined with transport capacity, our results suggest that the cut-fill terraces of western Peru can result from transient stripping of hillslope sediment but not steady-state hillslope erosion.