Earth and Atmospheric Sciences, Department of


Date of this Version



Published in Geomorphology 27:3–4 (March 1999), pp. 295–306; doi: 10.1016/S0169-555X(98) 00080-4


Copyright © 1999 Elsevier Science B.V. Used by permission


A prehistoric rockfall, probably caused by an earthquake with a magnitude of 5.0 or greater, blocked Río de las Conchas 2 km upstream from Alemanía (Salta Province, Argentina) in the southern part of the Cordillera Oriental. The rockfall created a dam that formed a lake at least 16 km long. Shells of Biomphalaria, preserved in the lake sediments and, dated by radiocarbon, established the time of this event to be about 5500–6000 years ago. When the natural dam failed, probably either by piping or overtopping, the lake drained catastrophically, eroding a trench through the chaotic mass of sandstone rubble.