A high-altitude volcanic complex
Nevado Ojos del Salado is a stratovolcano, a large, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Straddling the border of Chile and Argentina, it is the highest active volcano on Earth, with a summit elevation of 6,893 meters (22,615 feet). This makes it the second-highest mountain in both the Western and Southern Hemispheres, surpassed only by Aconcagua, which is 6,961 meters tall. The volcanic complex is not a single peak but a collection of overlapping lava domes and craters spread over an area of up to 160 square kilometers.
The volcano's rock composition is primarily dacitic, with some andesite and rhyodacite. These are types of volcanic rock that are rich in silica. The lavas contain minerals such as plagioclase, hornblende, biotite, and augite. Geologically, Ojos del Salado is located in the Central Volcanic Zone of the Andes, a region formed by the subduction of the Nazca Plate beneath the South American Plate. Volcanic activity in this area began around 26 million years ago.
Despite its great height, the mountain's location near the Atacama Desert results in extremely arid conditions, which prevent the formation of large glaciers. Snow cover is typically present only during the winter. The last confirmed eruption occurred around 750 CE. However, fumarolic activity, the emission of steam and volcanic gases, persists, and a possible steam emission was reported in November 1993, confirming its status as an active volcano.
The world's highest lake
A permanent crater lake exists near the summit of Ojos del Salado, at an elevation between 6,480 and 6,500 meters (21,260–21,330 feet). This body of water, approximately 100 meters (330 feet) in diameter, is the highest known lake of any kind in the world. The lake is fed by melting permafrost and surrounding snowfields and is located near active fumaroles. The water in streams feeding the lake can reach temperatures of 40.8°C (105.4°F).
This high-altitude aquatic environment is a subject of scientific study for its extremophile inhabitants. Researchers have found salt, acid, and cold-tolerant bacteria in the lake's sediments. These microorganisms are adapted to a unique combination of environmental stressors: low temperatures, acidic water (pH as low as 2.08), high solar radiation, and low oxygen. Bacterial communities identified include iron-oxidizing species like Ferrithrix and sulfur-processing bacteria such as Hydrogenobaculum. The study of these life forms shows the potential for life in similar harsh environments on other planets, such as Mars.