Llullaillaco

Llullaillaco (Spanish: [(ɟ)ʝuʝajˈʝako] or [ʎuʎajˈʎako]) is a dormant stratovolcano on the border between Argentina (Salta Province) and Chile (Antofagasta Region). It is part of the Llullaillaco National Park and lies in the Puna de Atacama, a region of tall volcanic peaks on a high plateau close to the Atacama Desert, one of the driest places in the world. Its maximum elevation is most commonly given as 6,723 metres (22,057 ft), making it the second-highest active volcano in the world. Despite its height, it is not clear whether the volcano has any glaciers or merely patches of perennial snow and ice. Between 3,700 m and 5,000 m elevation there is a sparse plant cover, while at lower altitudes the climate is too dry for plants to grow. A species of mouse on Llullaillaco is the vertebrate species living at the highest-known altitude.

The volcano formed during the Pleistocene in two stages, named Llullaillaco I and Llullaillaco II. The oldest rocks are about 1.5 million years old. About 150,000 years ago, the volcano's southeastern flank collapsed, generating a debris avalanche that reached as far as 25 kilometres (16 mi) from the summit. During the last stage, three conspicuous lava flows were emplaced on the summit. The youngest-dated rocks are 930 ± 140 years old, but there are reports of activity from the 19th century.

There are archaeological sites on the mountain and at its foot; Llullaillaco marks the highest archaeological site in the world. The first recorded ascent was in 1950. In 1999, the mummified remains of three children, known as the Children of Llullaillaco, were found at its summit. They are presumed to have been human sacrifices.

The name Llullaillaco is usually associated to the Quechua word llulla meaning "false", "lie" or "deceitful" and yaku or llaco meaning "water". This name probably refers to meltwater from snow, which flows down the slopes but then is absorbed into the soil; normally mountains are sources for water. Another possibility is that it refers to the danger from floods in the local valleys. Other translations are (Aymara) "hot water" after lloclla "warm" and yacu "water", and (Quechua) "thinking", "memory"+"water" or "thing that hardens after forming tender" llullu, which may refer to volcanic activity.

Llullaillaco is located in the northwestern Argentine Andes, towards the southern end of the Puna. The frontier between Argentina and Chile passes over the mountain. The Argentine portion is in the Los Andes Department of Salta Province and the Chilean in Chile's Antofagasta Region. About 30 km northeast of Llullaillaco, the Salta–Antofagasta railway crosses the Andes at Socompa. Humans first moved into the area about 8,000 BCE. The region was inhabited by hunters and shepherds in pre-Hispanic times. At some point between 1470 and 1532 CE, the Inca empire occupied the region.

There are numerous abandoned mines in the region, and the active lithium production plant "Proyecto Mariana" at the Salar de Llullaillaco. Azufrera Esperanto is an abandoned sulfur mine north of Llullaillaco and is associated with an area of hydrothermal alteration. The mine can be reached through a road or path from the northwest. Another abandoned mine lies south of the volcano. Mina Amalia is an abandoned borate mine and Mina Luisa and Mina Maria abandoned salt mines at Salar de Llullaillaco. A weather station installed on Llullaillaco in 2004 was for some time the highest in the world. The region is dry and located at high altitudes, making work in the area difficult. The extreme environmental conditions have been compared to conditions on Mars.

The volcano is an imposing mountain, rising by 3,800 m and 3,750 m above the Salar de Punta Negra and the Salar de Llullaillaco, 36 km and 20 km away, respectively. With a summit height of 6,723 m, (or 6,739 m) it is one of the highest mountains in the Andes (third highest in Chile and seventh highest in the Andes, according to John Biggar) and the second- or third-highest volcano in the world (Ojos del Salado is the highest). In the early 20th century, Llullaillaco was thought to be the highest volcano in the world. The elevation is to a large degree consequence of the underlying terrain, which rises about 4 km above sea level. The height of the mountain and the clear air in the region make Llullaillaco visible from Cerro Paranal, 190 km away as measured through Google Earth. The view from the mountain extends from Licancabur north over the Nevados de Cachi mountains east to Ojos del Salado 250 km south; mountains in between are visible as well.

Llullaillaco is a composite volcano formed mostly by lava flows. It rises about 2.2–2.5 km above the surrounding terrain and hundreds of metres above surrounding mountains. The summit of Llullaillaco is formed by a small cone with about four associated lava domes, which reach lengths of 1–3 km and have abrupt walls. Three hollows, probably volcanic craters, lie east of a 200-metre-long crest at the summit. The slopes of the volcano are fairly steep, with an altitude drop of 1,800 m over only 3 km horizontal distance. The slopes high up are steeper than those at lower altitudes. A plateau at 5,600–6,100 m elevation is the remnant of an eroded crater from an early stage in Llullaillaco's development.