Llullaillaco
Llullaillaco is a dormant stratovolcano on the border between Argentina and Chile. 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, 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 and 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 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.
Name
The name Llullaillaco is usually associated to the Quechua word meaning "false", "lie" or "deceitful" and or 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 "hot water" after lloclla "warm" and yacu "water", and "thinking", "memory"+"water" or "thing that hardens after forming tender" llullu, which may refer to volcanic activity.Geography and geomorphology
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 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.
Geomorphology
The volcano is an imposing mountain, rising by and above the Salar de Punta Negra and the Salar de Llullaillaco, and away, respectively. With a summit height of, it is one of the highest mountains in the Andes and the second- or third-highest volcano in the world. 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 above sea level. The height of the mountain and the clear air in the region make Llullaillaco visible from Cerro Paranal, 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 south; mountains in between are visible as well.Llullaillaco is a composite volcano formed mostly by lava flows. It rises about 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 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 over only horizontal distance. The slopes high up are steeper than those at lower altitudes. A plateau at elevation is the remnant of an eroded crater from an early stage in Llullaillaco's development.
Three young-looking, long lava flows emanate from the summit cone to the north and south. Morphologically, these flows are reddish-black aa lava flows and feature black and reddish glassy blocks with sizes of. The fronts of the stubby, lobe-shaped flows are up to thick. The northern flow has prominent levee-like structures and splits into a northwestern and northeastern branch upon reaching an obstacle. The southwestern lava flow is long and was fairly viscous when it was erupted. It almost reaches a road southwest of the volcano. The third flow is just east from the southwestern and descends an altitude of. The flows have levee-like structures and ridges. On the northern flank is Azufrera Esperanto, a 5,561-metre-high eroded volcano with sulfur deposits and traces of hydrothermal alteration. The existence of a cave on Llullaillaco is doubtful. The edifice covers an elliptical area of with about — of volcanic rock. The ground at Llullaillaco is formed mostly by lavic rocks and block debris, which are frequently buried by tephra. The rocks are grey, except where weathering has coloured them black, brown, red or yellow, and their appearance is vitrophyric or porphyritic.
Several dry valleys originate on Llullaillaco, including Quebrada de las Zorritas on the north-northeastern slope, Quebrada El Salado and Quebrada Llullaillaco on the northwestern slope, and Quebrada La Barda on the southwestern slope. Most of the dry valleys drain into Salar de Punta Negra. There is little erosion by water, and the valley network is poorly developed. There is water only episodically, during snowmelt. Only Quebrada de las Zorritas carries permanent water. There is a permanent spring there, possibly in Quebrada de Llullaillaco and Quebrada de Tocomar as well, while there are no known springs on the Argentine side of Llullaillaco. Darapsky in 1900 reported the existence of warm springs at Ojo del Llullaillaco and Ojo de Zorritas.
Several small lakes are found at elevation. At elevation on the northwestern flank is Lago Llullaillaco lake, a frozen waterbody. It is one of the highest lakes in the world.
Debris avalanche
A major landslide occurred in the volcano's history during the late Pleistocene, probably triggered by volcanic activity. This landslide descended the eastern-southeastern flanks of the volcano into Argentina, first over a steep slope of 20° on the volcano, split around Cerro Rosado and entered the Salina de Llullaillaco east of the summit, extending up to into the salar. The toe of the avalanche reaches a thickness of above the salar in the avalanche's southern lobe. Part of the avalanche was channelled in a valley between Cerro Rosado and an unnamed volcano farther south. When it reached Cerro Rosado, the avalanche climbed about and mostly continued to flow southeast into the main avalanche path, with only a small flow continuing northeastwards. Part of the run-up avalanche later collapsed backward over the main avalanche deposit. Unlike Socompa farther north, a landslide scar is only poorly developed at Llullaillaco despite the large size of the collapse; it was largely filled in later by lava flows and volcaniclastic debris.This landslide has been subdivided into four facies and features landforms like levees up to high, longitudinal ridges and a run-up mark on Cerro Rosado. Such ridges may be associated with uneven underlying terrain. The surface of the slide is covered by lava bombs less than long, blocks exceeding width, cobbles, and gravel-like rocks. The largest blocks with sizes of up to are found close to the collapse scarp. Overall, the margins of the landslide are very crisp and the surface covered by hummocks.
The landslide deposit covers a surface of about. Its volume has been estimated at and the speed at. This speed range is comparable to that of the Colima, Lastarria, and Mount St. Helens debris avalanches. The landslide occurred no earlier than 156,000 to 148,000 ±5,000 years ago; it might coincide with the 48,000-year-old lava flow. Another possibility is that the collapse took place in multiple failures. Some volcanic rocks were still hot at the time of the collapse, indicating that volcanic activity occurred immediately before the collapse. A smaller undated avalanche occurred on the northeastern flank.
Such landslides are common at volcanoes, where they are favoured by the steep edifices that form from lava flows being stacked on top of each other. It is not usually known what triggers the collapse, although eruption-associated earthquakes are suspected to play a role. Other volcanoes in the region with sector collapses are: Lastarria, Ollague, San Pedro, Socompa, and Tata Sabaya. The Mellado and Cerro Rosado volcanoes close to Llullaillaco also display evidence of sector collapses.
Geology
Regional setting
Volcanism in the Andes is caused by the subduction of the Nazca Plate and the Antarctic Plate beneath the South America Plate. The Nazca Plate subducts at a speed of and the Antarctic Plate at a speed of. Volcanism is not continuous along the Andes; rather it occurs in four distinct volcanic zones: Northern Volcanic Zone, Central Volcanic Zone, Southern Volcanic Zone and Austral Volcanic Zone. The formation of magma results from the release of water and other volatile material from the subducting plate, which is then injected into the above-lying mantle wedge. The volcanic zones are separated by gaps, where subduction occurs at a flatter angle due to the presence of ridges on the downgoing plate: The Nazca Ridge in the gap between the NVZ and CVZ, the Juan Fernandez Ridge in the one between the CVZ and SVZ, and the gap between the SVZ and AVZ is associated with the Chile Triple Junction. Minor ridges are associated with decreased volcanism rather than its cessation; the Taltal Ridge projects under Llullaillaco, an area where magma output was less than to the north and south.About 178 Holocene volcanoes are found in the Andes, 60 of which have been active in historical times. In addition, there are large calderas and monogenetic volcanoes.
Llullaillaco is one of more than 1,000 volcanoes in the CVZ. At least 44 volcanic centres with historical activity and 18 large caldera-forming volcanoes have been identified in the Central Volcanic Zone; the most active is Lascar, and Guallatiri and San Pedro have had historical eruptions as well. Volcanism in the Central Volcanic Zone takes place mostly on the Altiplano and the Cordillera Occidental, where high stratovolcanoes with heights of over occur. One of the largest vertical drops on Earth, almost, exists between the summit of Llullaillaco and the Peru-Chile Trench farther west. The Wadati-Benioff zone lies at depth.