A progressive uplift of the terrain around Lastarria and farther south has been recognized; it appears to reflect a deep magma intrusion in the region.

Lastarria is situated in the Central Andes, in the Antofagasta Region of Chile, and straddles the border with Argentina's[2][3] Salta Province.

[9] Lastarria is part of the Andean Central Volcanic Zone,[3] which extends over 1,500 kilometres (930 mi) from Peru to Chile.

[16] Most of the volcano is covered by pyroclastic material,[17] some of which extends to the southeastern margin of the Salar de Aguas Calientes.

[22] Volcanic activity has migrated north during the history of Lastarria, and the most recent eruption products are found on the northern and western slopes.

[24] Much of the surface, including the Southern Spur, is covered by deposits left by volcanic ash fall.

[1] It is formed by several massive flows erupted from a single vent during three or eight pulses;[13][14] the longest reaches a length of 10 kilometres (6.2 mi).

[28] Water levels in the lake were higher in the past, as evidenced by two recognizable shorelines,[29] which owing to tectonics related to recent volcanism in the Corrida de Cori crop out mainly on the eastern side,[30] and the lake's surface area reached 18 square kilometres (7 sq mi).

[32] A major sector collapse occurred on Lastarria's southeastern flank, leaving a clearly defined north–south scarp in the volcano that opens to the east-southeast.

[33] The debris avalanche deposit is 8 kilometres (5.0 mi) long and well preserved[34][2] with landforms such as lobes, levees and hummocks.

[35] After exiting the collapse scar over its northern opening, it overrode an older scoria cone before coming to rest.

[40] The avalanche deposit consists mostly of loose material such as ash, lapilli, pumice, with only a few lithic blocks.

It is comparable to the volume of the landslide that the Ancash earthquake triggered on Huascarán in Peru in 1970, resulting in more than 20,000 fatalities.

[14] Magmatic processes important in the Central Andes include the partial melting of the subducting plate and its sediments and of mantle peridotite, and fractional crystallization of ascending magma in the crust.

[12] During the late Cenozoic, a volcanic chain was formed on top of Mesozoic and Paleozoic rocks and reached a width of 100 to 150 kilometres (62 to 93 mi) in the area of Lastarria.

[3] Lastarria and Cordón del Azufre form a group of volcanoes on the Altiplano, on the border between Chile and Argentina.

[48] Farther south lie volcanoes such as Wheelwright Caldera and Cerro Blanco, the last of which shows evidence of recent unrest.

They are of Miocene to Pleistocene age[20][13] and are in turn underlaid by Paleozoic metamorphized volcanic and sedimentary rocks.

[51] Other lineaments in the region include the Imilac-Salina del Fraile and Pedernales-Arizaro faults of Miocene age.

[14] Phenocrysts include plagioclase in andesite with smaller amounts of amphibole, biotite, clinopyroxene, and orthopyroxene.

[13] They broadly consist of several components, mainly native sulfur, sulfates like anhydrite, baryte, gypsum and rhomboclase, borates like sassolite, oxides like quartz and less commonly sulfides like galena, orpiment and pyrite.

The Negriales rocks are the richest in silicon dioxide, and their trace element composition sharply diverges as well.

[65] Lastarria has a montane climate characterized by extreme aridity as it is located at the intersection between the summer rain region of the Altiplano and the Atacama Desert.

[53] It manifests in fumaroles forming 15-centimetre (5.9 in) high chimneys, small cones reaching heights of 2 metres (6 ft 7 in), 2.5 metres (8 ft 2 in) wide craters, 100 by 50 centimetres (39 by 20 in) fractures, in a diffuse fashion through pyroclastic deposits, as well as degassing through cracks and fissures on surfaces.

[88] The gases of Lastarria come from a geothermal system and, with temperatures ranging from 280 to 370 °C (536 to 698 °F) and 560 to 680 °C (1,040 to 1,256 °F), supply the colder and hotter fumaroles, respectively.

On Earth, they have been found at Kawah Ijen in Indonesia, Mount Iō (Shiretoko) in Japan, Mauna Loa on Hawaii, Momotombo in Nicaragua, and Sierra Negra on the Galapagos Islands.

[101] InSAR observations performed in the years 1998 to 2000 have yielded evidence of a pattern of ground uplift centered between Lastarria and Cordón del Azufre.

[20] This uplift appears to be caused by the injection of magma at depth, with a pattern of progressively increasing flux between 2003 and 2006.

[44] This uplift may have been ongoing for about 400,000 years and has influenced the final position of lava flows of Lastarria and other volcanoes in the area.

[106] Modelling indicates that the source of this uplift lies at a depth of about 1,000 metres (3,300 ft) and has the shape of a sphere.