EXTREME FLOODING IN A HYPERARID REGION: HYDROLOGIC AND GEOMORPHIC ANALYSIS OF THE 2015 ATACAMA FLOODS, CHILE

In March 2015 unusual atmospheric conditions over the Atacama Desert of northern Chile, one of the driest regions on Earth, produced many years’ worth of rainfall in a ~48-hour period, resulting in catastrophic flooding. Here we describe the hydrologic and geomorphic drivers of and responses to the 2015 Atacama floods. The flood had a remarkably high sediment load, which was primarily derived from dramatic erosion of channel bed, bank, and floodplain material (i.e., valley fill), and that hillslopes remained surprisingly intact despite their lack of vegetation. In the coastal city of Chañaral, flooding of the Salado River produced maximum water depths over 6 m, meters-thick mud deposition in buildings and along city streets, flow velocities larger than 8 m/s, and coastal erosion. The Atacama flooding has broader implications for hazard reduction and in light of both mining-related contaminant transport in the affected watersheds and the Atacama’s status as a terrestrial analog for Mars.