The southern slopes of Tunupa are incised by the shorelines of former lakes that occupied the Altiplano, such as Lake Minchin and Lake Tauca. Crusts of algae, stromatolites and river deltas are also found at these former shorelines. Over seven separate shoreline stages have been identified at Tunupa, which was part of an island in Lake Tauca. It is likely that evaporation from the lake increased precipitation at Tunupa and thus allowed glaciers to grow to larger sizes than they would have without such evaporation.