Although clouds cover most of the upper image (west), a small part of the Darwin Range ice field can be seen near the center; meltwater from the glacier enters the grayish-blue waters of Lake Viedma (lower right). The lake color is a result of the water containing rock flour – finely ground rock particles that are carried into glacial lakes by meltwater and remain in suspension. The ice fields of the southern Andes are remnants of a much larger glacier that covered the area 15,000 years ago. Melting of that large glacier started 13,000 years ago. During a glacial advance erosion caused by entrained boulder under the ice as well as the weight of the glacier creates basins. As glaciers in Argentina retreated, these large basin or troughs filled with meltwater to form the lakes that currently dot the area. The smaller present-day glaciers or ice fields are fed by the cool, moist westerly winds off the Pacific Ocean. The melting glaciers feed the lakes with fresh water. The outlet of Lake Viedma flows into Lake Argentino to the south. Lake Argentino is the source for Santa Cruz River, which flows eastward across Patagonia and into the Atlantic Ocean.
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