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Andagua volcanic field

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Elevation  4,713 m
Geology  Volcanic field
Andagua volcanic field httpsuploadwikimediaorgwikipediacommonsthu
Similar  Auquihuato, Cerro del Azufre, Reclus, Viedma, Cochiquito Volcanic Group

The Andagua volcanic field (also known as Andahua) is a volcanic field in southern Peru. Located between the Coropuna and Sabancaya volcanoes, it is formed from a number of lava domes and scoria cones that have generated lava flows. Activity ranges from the early Pleistocene until historical times.

Contents

Map of Andahua-Orcopampa, Peru

Geography

The field is located in the Orcopampa, Andahua and Ayo valleys, between the Coropuna and Sabancaya volcanoes. In the Andagua valley it runs from Orcopampa to the intersection with the Colca valley. The volcanic field has dimensions of 12,000 square kilometres (4,600 sq mi) and is located 20 kilometres (12 mi) northeast of Coropuna volcano, north of the Colca River. More than 15 centres cluster in an area of 40 by 6 kilometres (24.9 mi × 3.7 mi). The field is subdivided into seven subfields, Antapuna, Colca Valley, Huambo-Cabanaconde, Laguna Parihuana, Molloco Valley, Pampa Jarán and Valley of the Volcanoes. The Valley of the Volcanoes is 90 kilometres (56 mi) long and is a graben with numerous fault zones.

Coropuna, Sabancaya and El Misti are volcanoes adjacent to this group. Coropuna rises 3,000 metres (9,800 ft) above the surrounding terrain. The latter two have been active in historical times and belong to the Barroso Group of stratovolcanoes. The field is located at the northern end of the Central Volcanic Zone where it ends into the Peruvian flat-slab subduction area, where no recent volcanism is present.

Geology

The volcanic field is located in the Western Cordillera, on 60–80 kilometres (37–50 mi) thick crust. The main volcanic arc is located here, with a Wadati-Benioff zone 120–130 kilometres (75–81 mi) deep. The arc is now 230 kilometres (140 mi) long. A number of fault systems and orogenic events occurred in the area during the Cretaceous-Paleogene. Volcanic activity resulting in the formation of calderas in the Miocene and ores from hydrothermal activity. The volcanoes are constructed on Jurassic Yura Group sandstones and Pleistocene alluvium.

The number of individual centres observed varies, roughly 121 lava domes and 46 pyroclastic cones, one of which, Gloriahuasi, more akin to a small stratovolcano. They are comparable to many other Central Andean scoria cones. Many of them predate the last glaciation, given the degree of weathering and aeolian burying. The youngest of these are located in the Andagua valley. Jenchaña (15°32′S 72°19′W) has the longest lava flow of the field, reaching 10 kilometres (6.2 mi) down almost to the Colca canyon. These cones have heights of 200–300 metres (660–980 ft) and diametres of 500–600 metres (1,600–2,000 ft). Most centres are located on the valley floors but a few formed in their shoulders; these frequently contain xenoliths. Lava flows have volumes of around 15 cubic kilometres (3.6 cu mi) and lengths between four and eight kilometres. The valleys are filled with flows that reach a thickness of 130 metres (430 ft) in the Ayo valley. Total volumes reach 15 cubic kilometres (3.6 cu mi). Activity is mostly strombolian in nature and has formed steep cones and blocky lava flows.

The formation of this field is linked to the rifting of the Andahua valley, as well as local stress fields. A north-south extensional regime has been interpreted to have reactivated a fault system deep enough to permit magma ascent.

The cones have generated basaltic-andesitic lavas with SiO2 of 54.5%-59.65%. The petrology suggests that the lavas from the field formed in deep magma chambers with little contamination in shallow level magma chambers. Plagioclase is the main component of most lavas, with subordinate clinopyroxene. Basaltic andesites and in lesser measure andesites contain olivine, hornblende and orthopyroxene are found in andesites and biotite only in evolved dacites. Microlithic and microcrystalline textures prevail. Some lavas have been described as benmoreites and mugearites.

Activity from this field has dammed rivers in the area. Laguna de Chachas was dammed by lavas erupted from the Antaymarca area. Puca Mauras volcano is the single largest centre in the area with a volume of 7 cubic kilometres (1.7 cu mi). It has erupted highly derived magmas, including trachytes and latites.

Eruptive activity

Pleistocene activity has been dated 270,000 years ago for a sample south of Cerro Ticsho and 500,000 years for another south of the Yanamauras cones. These dates are derived from potassium-argon dating.

The first Holocene activity occurred 8770 BP. The Ticsho and Puca Mauras cones formed 4060 BP and Keyocc 2810-2970. The 2650 BP Mucurca tephra is linked to this volcanic field. Chilcayoc cone is the youngest cone and dated between 1451-1523 AD. All Holocene dates are based on radiocarbon analysis. One report describes that buildings have been damaged by activity. Sapper reported an eruption 6 March 1913 and activity during the Inca era. Emission of hydrogen sulfide from Niñamama dome was reported in 2003.

Volcanic hazards

Future volcanic activity in this field is likely. While activity is unlikely to be of large magnitude or cause fatalities, blockages of the valley or phreatomagmatic activity even if not recorded in the field so far may disrupt the valley communities.

References

Andagua volcanic field Wikipedia


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