Licancabur to the north, La Pacana southeast and Guayaques to the east are separate volcanic systems.

[11] Purico is part of the Central Volcanic Zone (CVZ), a belt of volcanoes that runs along the western margin of South America between 14° and 28° southern latitude.

[13] Purico is a circular shield with a diameter of 15–25 kilometres (9.3–15.5 mi), whose slopes descend away from a centre at an elevation of 5,000 metres (16,000 ft).

[9] To the west, close to the margin of the Salar de Atacama, the shield drops down to a bajada[b].

[16] A north-south trending system of fractures and conspicuous normal faults cuts across the western margin of the Purico complex.

[9][20] Lahars and debris flows from the volcanoes have covered parts of the ignimbrite shield with gravels.

[21] A meltwater-fed spring on Cerro Toco is known as Aguada Pajaritos, and a small lake Laguna de Agua Amarga is found south of Chascon.

[30] Ignimbritic activity in such systems is episodic, being interrupted by periods with lower volume "steady state" volcanism.

[26] The eruption of the Purico ignimbrite is the youngest large ignimbrite eruption in the Altiplano-Puna volcanic complex;[31] the Altiplano-Puna volcanic complex presently is in such a "steady state" stage,[3] but the presence of active geothermal system indicates that magmatic activity is still ongoing.

[3] Varying amounts of phenocrysts occur in the Purico complex rocks; the minerals they are formed of include augite, biotite, clinopyroxene, hornblende, hypersthene, iron oxides, oligoclase, orthopyroxene, plagioclase, quartz and titanium oxides.

[40] The climate at Purico is cold, with annual mean temperatures of −3 – −4 °C (27–25 °F);[11] during summer it hovers around 0 °C (32 °F) and during winter it can decrease to −6 °C (21 °F).

[43] Llano del Chajnantor features the world's highest insolation,[44] which under particular meteorological conditions can approach that at Venus.

[48] This dry climate is due to the combined effects of the subtropical ridge, the Humboldt Current in the Pacific Ocean and the rain shadow exercised by the Andes, but it was in the past interrupted by wet periods.

[5] Conversely, the soils on the Purico complex contain a diverse population of microbes[52] which have to tolerate extreme environmental conditions.

[60] Increased moisture availability during the ice ages caused the development of glaciers on Purico;[61] at times, an ice cap with outlet glaciers[62] covered an area of 200 square kilometres (77 sq mi)[63]-250 square kilometres (97 sq mi) at 5,000 metres (16,000 ft) elevation on Purico.

[68] It was originally called Cajon ignimbrite and attributed to an area northwest of Purico known as Chaxas.

Also, the Toconao ignimbrite was originally attributed to the Purico complex,[7] but now the La Pacana caldera is considered to be its source.

[4] The 2 cubic kilometres (0.48 cu mi) large[70] "dacitic dome D" has an age of 980,000 ± 50,000 and may thus have formed at the same time as the ignimbrites.

[4] The emplacement of the Purico ignimbrite was part of a pulse of activity in the Altiplano-Puna volcanic complex 1 million years ago.

The upper Lower Purico Ignimbrite is more heterogeneous, starting with a base surge, a pumice layer and then another flow unit,[37] which is volumetrically the largest part.

Prior to the Purico ignimbrite eruption, a dacitic magma chamber already existed beneath the volcano.

They are thus old volcanic centres and deeply eroded, displaying moraine deposits from glaciation and rocks which have been subject to hydrothermal alteration from fumarolic activity.

El Chascon especially may be only tens of thousands of years old, seeing as it displays both a summit crater and pristine lava flow structures.

[37] This change in the pattern of eruptive activity from large ignimbrites to smaller domes reflects a change in the nature of the magma supply, from large volume flow that heavily interacted with the crust and gave rise to the ignimbrites to smaller volume flows in a colder and thus brittler crust and did not accumulate or interact with it in a significant way.

[86] Macon stratovolcano is considered to be of Holocene age, and Alitar maar displays active fumaroles[1] and hot springs.

Fumarolic gases are mostly water vapour, with lesser amounts of carbon dioxide,[89] and sulfur deposition takes place.

[84] They appear to originate from both magmatic and precipitation water, with a large contribution from atmospheric air[90] and an important role for a hydrothermal system.

[93] In the 1950s[84] and as recently as 1993, sulfur was mined on Purico and transported by truck to San Pedro de Atacama where it was processed.