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Surface runoff, channel activation and sediment transport processes in desert environments have been convincingly shown to strongly depend on the duration and intensity of local and convective rainfall events. Among these environments, the Atacama, considered the driest desert on Earth, is situated in a remote and rugged area, where documentation of historical and recent hydro-sedimentary processes is rare. We characterize the hydrological processes in an endorheic watershed of the Atacama's Altiplano Desert, where the occurrence of flash floods was evaluated on event-based signatures of water and sediment in a small ephemeral playa. Twelve pits were dug in the playa, with five identified event sediment couplets, each corresponding to computed flood volumes that gave rise to transport and depositional events occurring between 1978 and 2019. Detailed topography allowed reconstruction of a 3D terrain model, from which we estimated a 11.3 t/yr/km2 local historic sediment yield. The timing of the older identified events did not match local rainfall records, and proved to be uncorrelated with occurrences of El Niño–Southern Oscillation (ENSO). This suggests a high spatial patchiness of rainfall events in terms of depth and intensity, and implies that small playa records are not necessarily always helpful in reconstructing the regional climatic history of the recent past. The sediment concentration and volume of the reconstructed hypercontracted events are not well corrected with the magnitude of the rainfall event, suggesting the important role played by variable sediment availability and connectivity at basin scale. This spatiotemporal variability plays a major role in understanding the present and historic hydro-sedimentary processes in the Atacama's altiplano. [Display omitted] • Five recent sediment-laden flood events have been identified in sedimentary records in a playa in the Atacama Desert. • Events are not directly related to ENSO episodes nor to regional climatic events. • Sediment concentration does not correlate with the magnitude of the rainfall event. [ABSTRACT FROM AUTHOR]

Abstract: 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 ∼1–20years 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 (1–3h, >4mmh−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. [Copyright &y& Elsevier]

Abstract: The Mejillones Peninsula in the coastal Atacama Desert of northern Chile is a region in which ocean–atmosphere–land interactions are particularly strong, resulting in enhanced alongshore winds that erode the surface and transport sand particles to the sea. Because the aeolian particles in the laminated sediments at the bottom of Mejillones Bay record long-term changes in the intensity of prevailing southerly winds, it is fundamental to understand aeolian processes such as wind erosion and sand transport to improve paleoceanographic reconstructions. The aim of the present study is to characterize the wind erosion process over the flat geomorphology of the northern portion of the Mejillones Peninsula, the Mejillones Pampa, including the influence of wind erosion on the initial particle size distribution and the associated fractionation processes of the mineralogical composition of moving particles, through field measurements. In addition, we test the ability of an existing saltation model (MB95) to reproduce the variability of the erosion process during the field experiment. Soil samples from 17 locations on this flat surface contain significant amounts of highly erodible particles with diameters in the 200–300µm and 100–150µm size ranges. Aeolian particles collected in BSNE sand traps located at different heights near the surface, exhibit a bimodal size distribution similar to that of the erodible fraction of the soils; the abundance of the fine class increasing with height. Small stones that have a spatially variable distribution can locally reduce the intensity of wind erosion. The mineralogical composition of moving particles is similar to that of the soils, with quartz, feldspar and calcite as the most important minerals, followed by clay minerals, gypsum and amphibole. A value of u* t is calculated for each soil particle size class. Subsequently, the elementary contribution of each size class to the horizontal flux is calculated using White (1979)''s equation and the total flux is finally obtained by integration. The saltation model successfully reproduces the variability of the wind erosion process during the field experiment, but over-estimates the vertically integrated mass fluxes measured in situ by two orders of magnitude. [Copyright &y& Elsevier]