Driest Desert on Earth

The Atacama Desert, located in northern Chile along the western coast of South America, is recognised as the driest desert on Earth. Spanning roughly 1,000 kilometres (about 600 miles) between the Pacific Ocean and the Andes Mountains, the Atacama represents one of the most extreme environments on the planet. It is a region so arid that parts of it have recorded no measurable rainfall for centuries, making it even drier than the Sahara and the polar deserts of Antarctica.

Geographical Location and Extent

The Atacama Desert stretches across northern Chile, from the Peru–Chile border in the north to around Copiapó in the south. It lies between two major mountain chains:

• The Andes Mountains to the east, and
• The Chilean Coast Range to the west.

This narrow desert strip covers an area of approximately 105,000 square kilometres. The driest core region, known as the Atacama Plateau, extends through the Antofagasta and Tarapacá regions. Major nearby cities include Antofagasta, Calama, and Iquique.

Causes of Extreme Aridity

The Atacama’s extreme dryness results from a combination of geographic, climatic, and oceanographic factors that prevent moisture from reaching the area:

1. Rain Shadow Effect of the Andes: Moisture-laden winds from the Amazon Basin are blocked by the Andes Mountains, preventing rainfall on the western slopes.
2. Cold Humboldt (Peru) Current: The cold ocean current flowing along the Pacific coast cools the air above it, reducing its ability to hold moisture and creating a stable layer of cool air near the surface that inhibits cloud formation.
3. Subtropical High-Pressure System: The descending air of the subtropical high-pressure belt (part of the global Hadley Cell circulation) suppresses convection and cloud development.
4. Double Rain Shadow Effect: In addition to the Andes on the east, the Chilean Coastal Range to the west further blocks moist air from the ocean, resulting in an extremely dry corridor in between.

These combined factors make the Atacama one of the few places on Earth where some weather stations have never recorded rainfall since their installation.

Climate Characteristics

• Rainfall: Average annual precipitation is less than 1 millimetre, and in some areas, virtually zero. The driest parts—near Yungay and Calama—can go centuries without rain.
• Temperature: Despite its dryness, the desert experiences moderate temperatures due to its coastal location, ranging from 0°C at night to 25°C during the day.
• Humidity: The air is extremely dry, with relative humidity often below 10%.
• Fog (Camanchaca): Along the coast, occasional fogs form when moist air from the ocean meets the cold coastal current, providing limited moisture to plants and microorganisms.

Soil and Surface Conditions

The Atacama’s soil is composed mainly of salt flats, sand, and volcanic rock, with a high concentration of nitrates, sulphates, and chlorides. The soil is so dry and sterile that it closely resembles the surface of Mars. Indeed, NASA has used the Atacama as a terrestrial testing site for Mars rovers and astrobiology research.
Some areas contain caliche deposits, which are rich in sodium nitrate (Chile saltpetre) and were historically mined as a source of fertiliser and explosives before synthetic alternatives became common.

Flora and Fauna

Life in the Atacama is sparse but highly specialised. Only a few species have adapted to survive its harsh environment:

• Plants: In coastal areas, fog-dependent vegetation such as cacti, lichens, and small shrubs can grow.
• Animals: Limited to insects, reptiles, and small birds; further inland, the environment is too dry to support significant life.
• Microbial Life: Extremophile microorganisms capable of surviving in highly saline and dry conditions have been discovered, offering insights into possible extraterrestrial life forms.

During rare rainfall events, dormant seeds germinate rapidly, producing a spectacular “desierto florido” or “flowering desert,” where the landscape briefly bursts into colour.

Geological Features

The Atacama Desert is rich in striking geological formations, shaped by wind erosion, volcanic activity, and salt deposition. Major features include:

• Salar de Atacama: A vast salt flat formed by evaporation of mineral-rich water.
• Valle de la Luna (Valley of the Moon): Noted for its moon-like landscape of ridges and dunes.
• El Tatio Geysers: One of the world’s highest geothermal fields, located near the Andes.
• Chuquicamata Copper Mine: One of the largest open-pit copper mines in the world.

The desert also contains ancient Inca and pre-Columbian trade routes, and archaeological sites revealing early human adaptation to extreme conditions.

Human Settlement and Activities

Despite its harshness, the Atacama supports limited human settlement due to rich mineral resources. It contains some of the world’s largest deposits of:

• Copper (notably at Chuquicamata and Escondida),
• Lithium (in Salar de Atacama), and
• Nitrates and other minerals.

Towns and mining communities have developed around these resources. Modern desalination and pipeline systems provide water for industrial and domestic use.
Tourism has also grown, with visitors attracted by the desert’s surreal landscapes, clear night skies, and scientific significance. The region is home to the Atacama Large Millimeter/submillimeter Array (ALMA), one of the most advanced astronomical observatories in the world, taking advantage of the desert’s exceptionally dry and clear atmosphere.

Comparison with Other Deserts

While polar regions such as Antarctica and the Arctic are technically colder deserts due to minimal precipitation, the Atacama Desert is considered the driest non-polar desert on Earth. Unlike the Sahara, which receives occasional seasonal rainfall, the Atacama’s aridity is continuous and extreme.

Scientific and Environmental Significance

The Atacama Desert serves as a natural laboratory for studying:

• Astrobiology: Its Mars-like soil conditions help scientists understand the potential for life on other planets.
• Climate Change: Provides long-term data on extreme aridity and atmospheric stability.
• Geology and Mineralogy: Offers insight into ancient Earth processes and mineral formation.

Its fragile ecosystem is now protected through environmental regulations and sustainable tourism initiatives to prevent damage from mining and human intrusion.