Evolution of the Eastern flank of the North Patagonian Ice Field: The deactivation of the Deseado River (Argentina) and the activation of the Baker River (Chile)

Abstract

Patagonia had significant morphological changes when moraines at the foot of the Andes caused reversals in the drainage of rivers that crossed flat plateaus. Several examples of such basins are known from evidences of misfit valleys and the activation of short watersheds with rapids. The Deseado River drained the second largest lake of South America (Buenos Aires-General Carrera) and another glacial-valley system. The Deseado-Pinturas system conducted large amounts of water that satisfied herds of guanacos; paleoindians established to take advantage of such a quantity of proteins favored by the configuration of gorges at the upper valley (Cueva de las Manos site). However, during the shrinking of the North Patagonian Ice Field, the Baker River activated capturing the drainage of both basins towards the Pacific Ocean. The deactivation of the Pinturas and Deseado systems caused the lowering of progressive younger fluvial terraces, a record of hanging tidal flats at the inlet, and a progressive abandonment of the Las Manos site. The Baker River today supplies large amounts of water for planned hydroelectric dams. However, the watershed has not arrived into morphological equilibrium and recently suffered several Glacial-lake outbursts floods (GLOFs).