A desert is generally defined as an area that averages less than ten inches of precipitation per year. None is more dry than the Atacama Desert of Northern Chile, parts of which have never received measurable precipitation (at least since man has been around to observe).
Covering 70,000 square miles, between the Pacific Coast and the Andes Mountain Range, the Atacama encompasses a variety of terrain, covered mostly by salt flats, sand dunes and lava flows. Any precipitation arriving from the east is cut off by the high wall of the Andes and what little drifts in from the ocean is wrung out by the Coastal Mountains; the inflow of moisture from the Pacific is further blocked by the Humboldt Current, an upwelling of cold sea water that flows northward along the west coast of South America. Some coastal regions of the Atacama receive minimal but regular moisture from a dense marine fog, which condenses on the few cacti and desert shrubs that manage to survive there. At higher, foothill elevations of the Desert, snow may fall but quickly evaporates in the thin, dry air.
While the Atacama Desert has been intensely dry for 20 million years or more, human settlements have occupied the region for over 10,000 years. Irrigating crops by tapping the deep aquifer or by diverting snow melt streams, these hardy natives have also mined copper and sodium nitrate throughout the parched landscape. The Andes foothill region, known as the Altiplano and ranging from 10 to 14 thousand feet, is known for its hydrothermal features (including geysers) and its resident cameloids (llamas, alpacas and vicunas). Flamingos, attracted to its ephemeral, saline lakes, inhabit some parts of the Atacama.
