In southern South America, the maximum areal extent of ice during the Quaternary Period, the Greatest Patagonian Glaciation (GPG, [Mercer, J.H., 1983. Cenozoic glaciation in the southern hemisphere. Annual Reviews of Earth and Planetary Science 11, 99-132.]), occurred at 1.1 Ma and subsequent glaciations were overall less extensive. The GPG preceded global minimum temperatures and maximal volume of ice, which occurred in the last ~ 800 kyr, as recorded in the marine δO record. Significant modification of the drainage morphology of the southern Andes from a non-glaciated to glaciated landscape occurred throughout the Quaternary Period. We infer a non-climatic relationship between glacial modification of the mountains and the decreasing extent of ice and we discuss processes of landscape development that could have caused the trend. Specifically, these include modification of valleys, such as development from a V- to a U-shape, and lowering of mass-accumulation areas. Such changes would strongly affect glacial dynamics, the mass balance profile and mass-flux during succeeding glaciations, especially for low-gradient outlet glaciers occupying low areas. Other areas around Earth (at least where ice has been warm-based) also may exhibit a non-random trend of decreasing extent of ice with time, ultimately because of glacial erosion in the Quaternary Period.