The constant temperature inversion caused by the cool north-flowing Humboldt ocean current and the strong Pacific anticyclone contribute to the extreme aridity of the desert.

[8] The most arid region of the Atacama Desert is situated between two mountain chains, the Andes and the Chilean Coast Range, which are high enough to prevent moisture advection from either the Pacific or the Atlantic Ocean, creating a two-sided rain shadow effect.

[9] According to the World Wide Fund for Nature, the Atacama Desert ecoregion occupies a continuous strip for nearly 1,600 kilometres (1,000 mi) along the narrow coast of the northern third of Chile, from near Arica (18°24′S) southward to near La Serena (29°55′S).

[citation needed]The drier portion of this ecoregion is located south of the Loa River between the parallel Sierra Vicuña Mackenna and the Cordillera Domeyko.

[13] The geomorphology of the Atacama Desert has been characterized as a low-relief bench "similar to a giant uplifted terrace" by Armijo and co-workers.

[14] The intermediate depression (or Central Valley) forms a series of endorheic basins in much of the Atacama Desert south of latitude 19°30'S.

[25] The opening of the Tasmania-Antarctic passage allowed for cold currents to move along the west coast of South America, which influenced the availability of warm humid air to travel from the Amazon Basin to the Atacama.

[28] The presence of evaporite formations suggests that in some sections of the Atacama Desert, arid conditions have persisted for the last 200 million years (since the Triassic).

[35] However, some locations in the Atacama receive a marine fog known locally as the camanchaca, providing sufficient moisture for hypolithic algae, lichens, and even some cacti—the genus Copiapoa is notable among these.

Geographically, the aridity of the Atacama is explained by its being situated between two mountain chains (the Andes and the Chilean Coast Range) of sufficient height to prevent moisture advection from either the Pacific or the Atlantic Oceans, a two-sided rain shadow.

[9] Despite modern views of the Atacama Desert as fully devoid of vegetation, in pre-Columbian and colonial times a large flatland area there known as Pampa del Tamarugal was a woodland, but demand for firewood associated with silver and saltpeter mining in the 18th and 19th centuries resulted in widespread deforestation.

Owing to its otherworldly appearance, the Atacama has been used as a location for filming Mars scenes, most notably in the 2004 television series Space Odyssey: Voyage to the Planets.

The team duplicated the Viking tests in Mars-like Earth environments and found that they missed present signs of life in soil samples from Antarctic dry valleys, the Atacama Desert of Chile and Peru, and other locales.

[42][43] In June 1991, Antofagasta and Taltal and inland regions as far as Calama received unusual rainfall leading to formation of a series of mudflows that killed 91 people.

[49][50] Resulting floods triggered mudflows that affected the cities of Copiapo, Tierra Amarilla, Chanaral, and Diego de Almagro, causing the deaths of more than 100 people.

Cactus species here include the candelabro (Browningia candelaris) and cardon (Echinopsis atacamensis), which can reach a height of 7 m (23 ft) and a diameter of 70 cm (28 in).

Outside of these extreme areas, sand-colored grasshoppers blend with pebbles on the desert floor, and beetles and their larvae provide a valuable food source in the lomas (hills).

Other birds (including species of hummingbirds and rufous-collared sparrow) visit the lomas seasonally to feed on insects, nectar, seeds, and flowers.

Larger animals, such as guanacos and vicuñas, graze in areas where grass grows, mainly because it is seasonally irrigated by melted snow.

The oasis settlement of Pica has Pre-hispanic origins and served as an important stopover for transit between the coast and the Altiplano during the time of the Inca Empire.

[58] The coastal cities originated in the 16th, 17th, and 18th centuries during the time of the Spanish Empire, when they emerged as shipping ports for silver produced in Potosí and other mining centers.

At the end of the 18th century, Carlos IV defines the southern border of the Viceroyalty of Peru at the port of Nuestra Señora del Paposo.

In the 20th century, the nitrate industry declined and at the same time, the largely male population of the desert became increasingly problematic for the Chilean state.

[62] In 1918, geologist Juan Brüggen mentioned the existence of 23 socavones (shafts) in the Pica oasis, yet these have since been abandoned due to economic and social changes.

[62] The desert has rich deposits of copper and other minerals and the world's largest natural supply of sodium nitrate (Chile saltpeter), which was mined on a large scale until the early 1940s.

[citation needed] The towns include Chacabuco, Humberstone, Santa Laura, Pedro de Valdivia, Puelma, María Elena, and Oficina Anita.

[citation needed] The Atacama Desert is also the world's largest source of iodine-bearing minerals, with some areas having iodine concentrations hundreds of times larger than the average levels in Earth's crust.

[67] Because of its high altitude, nearly nonexistent cloud cover, dry air, and freedom from light pollution and radio interference from widely populated cities and towns, this desert is one of the best places in the world to conduct astronomical observations.

[71] A radio astronomy telescope, called the Atacama Large Millimeter Array, built by European countries, Japan, the United States, Canada, and Chile in the Llano de Chajnantor Observatory officially opened on 3 October 2011.

On 26 April 2010, the ESO council decided to build a fourth site, Cerro Armazones, to be home to the Extremely Large Telescope.