Climatic and Geomorphic Interactions on Alluvial Fans in the Atacama Desert, Chile

Alluvial fan surfaces in the Atacama Desert of northern Chile preserve evidence of recent, precipitation-driven, surface flows. Determining the hydrologic characteristics of these flows is important for understanding the effects of rare yet significant storms in the region. Flow reconstruction, runoff analysis, and comparison with climatological data yield surface activation recurrence intervals of ~1-20 years for three small fans and associated catchments proximal to Iquique and Antofagasta. Relatively short-lived and intense precipitation events (1-3 hour, > 4 mm/hr) are required to mobilize and transport the largest surface grains. Modeled discharges provide minimum constraints on the rates of precipitation that yield surface-forming flows in the hyper-arid region. The results of this study aid in understanding the evolution of various surfaces in the region. In particular, results provide a clear indication of the ability of a particular storm event --i.e., precipitation rate to activate a surface.