Resumen
We present a study on the glacial and paraglacial geomorphology of a Patagonian Cordillera Valley that is key to understanding evolution of the great lakes of Patagonia. 10Be cosmogenic nuclide exposure ages of ice-moulded surfaces from the Bayo River Valley confirm that the valley became ice-free before 13.4-14.2 ka. This valley constituted the first outlet of the Chelenko Lake, precursor of the General Carrera-Buenos Aires Lake (GCBAL), toward the Pacific Ocean. This age constrains the timing of the lake drainage reversal from the Atlantic Ocean to the Pacific Ocean. Alluvial fans and terrace levels recognized in the eastern segment of the valley at the same altitude as terrace levels observed in the GCBAL basin confirm that the Bayo Pass controlled the elevation of the lake once the drainage reversed to Pacific Ocean. 10Be cosmogenic nuclide exposure ages also confirm that the maximum advance of the Exploradores Glacier since its major retreat >13.4-14.2 ka ago occurred during the Little Ice Age, the last remnant of glacial drift in these valleys.