Chachani is a volcanic group in southern Peru, 22 kilometres (14 mi) northwest of the city of Arequipa.

During the Pliocene and early Pleistocene, the volcanic group produced large ignimbrites such as the La Joya, Arequipa Airport and Yura Tuff ignimbrites; afterwards the volcanic group proper grew in the caldera until about 56,500 years ago.

It is considered to be one of the most easily climbed mountains between 6,000 - 7,000 m high, although acclimatization and good physical health are required to ascend it.

[11] Volcanoes in the southern part of Peru include from north to south Auquihuato, Firura, Coropuna, Andagua volcanic field, Sabancaya, Ampato, Chachani, El Misti, Pichu Pichu, Ubinas which has erupted intermittently since 1954, Huaynaputina where a large eruption occurred in 1600, Ticsani, Tutupaca, Yucamane and Casiri.

[16] Chachani is an about 2 kilometres (1.2 mi)[a][b] high and 17 kilometres (11 mi) wide[12] complex[c] of lava domes, stratovolcanoes[6] and volcanic cones;[1] the highest summit is 6,057 metres (19,872 ft) high, making Chachani the 84th highest peak in the Andes.

[23] To the south of Chachani lie the Airport Domes,[20][e] a 8 kilometres (5.0 mi) wide lava shield[22] with two discernible vents[30] and a pristine appearance.

[26] A volcanic caldera associated with widespread ignimbrites in the Arequipa area may be located underneath Chachani;[31] to the north its outline is marked by a 20 kilometres (12 mi) wide amphitheatre while its southern part is continuous with the Arequipa depression and is generally poorly recognizable.

[32] The El Misti volcano later arose on the margin of the Chachani caldera, where it intersects the border of the Altiplano.

Glacial erosion and landslides have affected the volcanic complex,[28] forming cirques and U-shaped valleys and removing much of the original shape of the individual volcanoes.

[6] Permafrost[24] and rock glaciers however still exist at Chachani, especially close to Nocarane, and reach lengths of 1.8 kilometres (1.1 mi);[7] they are characterized by lobate appearances and their location at the foot of tall cliffs.

[37] The oldest volcanic rocks of the Western Cordillera are known under the name "Tacaza", and underwent erosion and folding before the next phase which is known as "Sillapaca".

[26] The terrain of the volcano is formed by volcanic rocks of Eocene to recent age, which overlie a Precambrian basement[35] and include widespread Neogene-Quaternary ignimbrites.

[45] Phenocrysts include augite, biotite, hornblende and hypersthene;[46] the rhyolites of the Arequipa ignimbrites additionally contain ilmenite, magnetite, plagioclase, quartz and sanidine.

[27] Under the influence of the cold Humboldt Current and the subtropical ridge, the region features an arid climate with less than 100 millimetres (3.9 in) annual precipitation in Arequipa.

[52] From 3,500 to 3,900 metres (11,500 to 12,800 ft) elevation cacti, herbs, Peruvian feather grass, yareta but also lichens and mosses grow on the slopes of Chachani and other regional volcanoes.

[56] The oldest volcanic formations linked to Chachani are the so-called "sillars", which are rhyolitic pyroclastic flows[57]/ignimbrites[58] containing pumice beds.

[59] The 16–24 cubic kilometres (3.8–5.8 cu mi) 4.8 million years old La Joya, the 18–20 cubic kilometres (4.3–4.8 cu mi) 1.65 million years old Arequipa Airport, and less certainly the 1.5 cubic kilometres (0.36 cu mi) early Pleistocene Yura Tuff as well as the Capillune Formation ignimbrites appear to have been erupted by Chachani or (in the case of the Yura Tuff) from a vent north of it.

[69] The city of Arequipa with about one million inhabitants and infrastructure such as the airport, hydropower plants and reservoirs are within range of Chachani[70] and human settlement has spread around its base.

[78] Chachani is the protector mountain spirit of Cayma[79] The people of Arequipa sometimes refer to Chachani as the "father" of El Misti (Pichu Pichu is the "mother") and ascribed to it the ability to influence the gender of newborn children, making them daughters.