Nov 072009
photo provided courtesy of Phillie Casablanca on Flickr Creative CommonsLocationPeru and Chile
Annual Rainfallat most,  1mm per year
Ageover 20 million years

Deserts are by definition the driest places on earth. Since water is so essential to life on Earth, deserts are tough places for organisms to carve out a niche, and the driest desert on earth is without parallel on the scale of harsh environments. The Atacama desert of South America receives such a negligible amount of rain that it’s difficult to even detect when it does fall. Indeed, the recorded average rainfall in this bone-dry desert was a mere 0.02 inches over 30 years. That’s as dry as it gets on planet Earth.

The Atacama Desert, like the Namib Desert and Australian Desert, lies adjacent to a coastline, stretching from Peru in the North to central Chile in the south. This narrow desert is bordered on the other side by the massive Andes Mountains, a spine of peaks that divides the entire continent of South America. Both of these factors, ocean and mountain, create the conditions that make the Atacama Desert so arid.

Ocean currents form half of the equation. The current that runs along the western coast of South America, the Humboldt Current, carries cold water from Antarctica northward. This water chills the surface of the Pacific, limiting the amount of water that evaporates into rain-forming clouds. Instead, a dense fog called the camanchaca, and thin, whispy stratus clouds are produced. Neither of these produce rain for Western South America south of Peru.

The second factor that limits rainfall in the Atacama Desert is the Andes Mountain chain. Like the Himalayas limiting rainfall in the Gobi Desert of Asia, the Andes form a barrier to any moisture coming from the Amazon River basin. Clouds are pushed up the slopes of these great mountains and deposit their rain on the side facing the East. Wedged between these two limiting factors  Рcold ocean currents and high mountains Рthe Atacama is lucky to receive any rainfall at all. To make matters worse, the majority of the desert lies in an inland depression, that blocks access to the moist fogs coming off the Pacific. These conditions have remained relatively unchanged for millions of years, and in addition to being the driest desert on earth, the Atacama desert is also one of the oldest.

photo provided courtesy of 22BB on Flickr Creative CommonsWhat life does exist does so primarily around what are called “lomas,” areas of higher elevation that receive some of the moisture from the camanchacas fog coming off the ocean. Very few plants can survive in the gaps between the lomas, and as a result, food chains do not form. Some regions of the Atacama desert are completely devoid of life. Among the hardy plants that inhabit the region are more than 60 species of cactus, influding 25 species unique to the region. A number of bat and bird species also live along the lomas. Most mammal species are confined to the lomas and on the foothills of the Andes, including the guanaco, a small relative of llamas.

Human settlement in the Atacama Desert is limited to areas that can obtain water. To the north, small villages crowd around rivers and mining operations. Closer to the coast, residents stretch large nets to catch the fog as it comes off the Pacific Ocean. The moisture condenses on the nets and then drips into trays and pipes that collect the drinking water in large reservoirs. Because of the overuse and contamination of rivers, this condensor method of capturing water is the only means of life for many people living in the region.

The Atacama Desert is a land of extremes, all of which tell a fascinating story of the way earth’s geosystems interact to produce a final product.

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