Nevado Tres Cruces

Nevado Tres Cruces
Tres Cruces from Ojos del Salado to the east. The higher south summit is on the left, the central summit on the right.
Elevation	6,748 m (22,139 ft)
Translation	Three crosses (Spanish)
Location
Nevado Tres Cruces Region III, Argentina-Chile border
Range	Andes Mountains
Geology
Type	Volcano
Age of rock	Pleistocene
Volcanic arc/belt	Cordillera Claudio Gay, Central Volcanic Zone
Last eruption	28,000 years ago.

Nevado Tres Cruces is a massif of volcanic origin in the Andes Mountains. It has two main summits, Tres Cruces Sur at 6,748 m and Tres Cruces Centro at 6,629 m and a third more minor summit, Tres Cruces Norte 6,206 m. Tres Cruces Sur is the sixth highest mountain in the Andes. The area was first surveyed in 1883 by Francisco San Román and the Nevado Tres Cruces National Park was established in 1994.

The volcano has an extended history of activity, going back at least 1.5 million years. A number of lava domes surround the complex and a number of craters lie on its summits. The main volcano is of rhyodacitic composition and has generated two major ignimbritic eruptions, one 1.5 million years ago and a second 67,000 years ago. The last eruption was 28,000 years ago but the volcano may still become active in the future.

Climate and Glaciation

The area has a desert climate, with nighttime temperatures below freezing and precipitation less than 29±14 mm in the local summer that quickly sublimates away, resulting in a lack of surface runoff and a barren landscape. The mean annual temperature is -2±4 degrees Celsius. The area is persistently very windy. The snowline altitude in the area is 5,800 metres (19,000 ft), higher than the Pleistocene altitude of 5,500 metres (18,000 ft). Small relic glaciers with surfaces of less than 1 square kilometre (0.39 sq mi) exist above 5,500 metres (18,000 ft) with moraines visible above 4,400 metres (14,400 ft). In 2000 a total ice surface of 1.1 square kilometres (0.42 sq mi) was reported on Tres Cruces.

Geology

Portezuelo Maricunga

The whole complex has been active for 1.5 mya and has generated two large scale pyroclastic eruptions, a first one 1.5 mya occurred on the western side of the volcano. It is fairly thin and covers Pliocene lavas. Otherwise, rhyodacitic lava flows, lava domes and various ash and tephra deposits also belong to this volcano. The three main volcanoes of the massif - Tres Cruces Norte (6,206 metres (20,361 ft)), Tres Cruces Centro (6,629 metres (21,749 ft)) and Tres Cruces Sur (6,748 metres (22,139 ft)) formed along a local fault zone. Tres Cruces Sur and Tres Cruces Centro are the sixth and eleventh highest mountains in South America.

The massif delimits the Salar de Maricunga and has an extent of 10 by 5 kilometres (6.2 mi × 3.1 mi). The principal edifices are small but steep, rising 800–1,600 metres (2,600–5,200 ft) above their bases. The northern cone is glacially eroded and has a crater 1 kilometre (0.62 mi) wide. The central edifice has a crater 500 metres (1,600 ft) and is inclined westward. The southern edifice is formed from an older western structure (0.8±0.5 mya) with two small craters and a glacial cirque, and an eastern edifice with a summit lava dome 2 kilometres (1.2 mi) wide and basal lava flows. A cirque cuts the dome on the southeastern side and contains a small glacier. The whole edifice and the adjacent Miocene El Plateado volcano, as well as the western flank of neighbouring Ojos del Salado volcano, are covered with a thick layer of pumiceous ash fall, probably produced by the collapse of an eruption column. Pliocene volcanic chain Cristi (2.5±1.3 mya), Lemp (2.8±0.3 mya) and Rodrigo (adakites 4.4 mya) north and Puntiagudo south is largely buried beneath the massif. Tomographic analysis of the area has indicated the presence of a large high-attenuation zone in the crust beneath Tres Cruces and the neighbouring Ojos del Salado volcano, which may indicate ongoing or incipient melting of the underlying crust.

Lava domes

Two minor lava domes La Espinilla and El Indio are present. La Espinilla formed within the crater (150 metres (490 ft) deep and 1.5–2 kilometres (0.93–1.24 mi) wide) of an explosive eruption. This dome is 200–250 metres (660–820 ft) wide and 45 metres (148 ft) high and formed 168±6 ka K-Ar. El Indio is located on the side of La Espinilla away from the main massif and is larger and older (350±40 ka K-Ar) than Espinilla. Other older lava domes lie on the western flank (2.1±0.3 ka K-Ar).

A major dacitic lava dome (150–200 metres (490–660 ft) thick and covering a surface of 3.5 by 5.5 kilometres (2.2 mi × 3.4 mi)) lies on the northwestern side of the massif, the vent is buried by younger deposits. The lava display flow banding and column jointing and has been K-Ar dated 1.4±0.4 mya.

Recent activity

Activity in the southernmost volcano has been dated at 280,000±22,000 years ago. The complex is linked to the eruption of the Tres Cruces ignimbrite 67,000 years ago, also known as Pampa Blanca. This ignimbrite is well exposed in the valley which separates the Tres Cruces and Ojos del Salado volcanoes, assuming thicknesses of 100 metres (330 ft) with a basal flow 15 metres (49 ft) thick. The youngest activity occurred 28,000 years ago and formed the summit lava dome of the southernmost volcano.

Hazards

The volcano has an approximate volcanic flux of 0.13 cubic kilometres per millennium (0.00099 cu mi/Gs), lower than other arc associated volcanoes. Nevertheless, with eruptive episodes being separated by gaps of about 40,000 years between the last episodes, dangerous eruptive activity in the future is possible even if the the thinly populated region means that major damage to infrastructure or danger to human life is unlikely.

External links

• Biggar, John (2005). Andes: A guide for climbers (3rd ed.). Castle Douglas (Scotland): Andes. p. 183. ISBN 0953608727. Retrieved 22 November 2015. 
• Andes Handbook (Spanish)
• Tres Cruces (Spanish) [1]
• [2]