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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 similar to 1-20 years for three small fans and their associated catchments proximal to Iquique and Antofagasta, Chile. Modeled discharges provide minimum constraints on the precipitation rates required to resurface fans in the hyper-arid region and suggest that relatively short-lived and intense precipitation events (1-3 h, >4 mm h(-1)) are capable of producing surface flows that mobilize and transport the largest grains found in channelized portions of the fan surface. The results of this study provide an indication of the ability of a particular storm event, i.e., precipitation rate, to activate a geomorphic surface and contribute to our understanding of the controls on surface evolution in hyper-arid environments. (C) 2010 Elsevier B.V. All rights reserved.