Cerro Blanco (Spanish: [ˈsero ˈβlaŋko], "White Hill") is a caldera in the Andes of the Catamarca Province in Argentina.

Part of the Central Volcanic Zone of the Andes, it is a volcano collapse structure located at an altitude of 4,670 metres (15,320 ft) in a depression.

About 2,300 ± 160 BCE,[1] the largest known volcanic eruption of the Central Andes, with a VEI-7, occurred at Cerro Blanco, forming the most recent caldera as well as thick ignimbrite layers.

[9] Provincial Route 34 (Catamarca) between Fiambalá and Antofagasta de la Sierra runs past Cerro Blanco.

[22] The caldera floor is almost entirely covered by block-and-ash flows, apart from an area where hydrothermal activity has left white sinter deposits.

This depression appears to have formed in response to north-south tectonic extension of the Puna[37] and is covered by volcanic deposits from Cerro Blanco.

[9] Various wind-dependent mechanisms have been proposed to explain their large size, including the presence of roll vortexes, Helmholtz instability-like phenomena, atmospheric gravity waves[51] or creep-like movement when pumice fragments and sand are lifted from the ground by wind and fall back.

[82] A series of andesitic to dacitic stratovolcanoes ranging in age from 1 to 6 million years old make up the Cordillera de San Buenaventura,[83][84] and Quaternary basaltic volcanoes are dispersed over the wider region.

[16] In the surroundings of Cerro Blanco lies the Cueros de Purulla volcano 25 kilometres (16 mi) north and the Nevado Tres Cruces-El Solo-Ojos del Salado complex farther west.

[91] The late mafic eruption products and the Cerro Blanco volcanics are geologically classified as making up the "Purulla Supersynthem".

[92] From the Miocene to the Pliocene the La Hoyada volcanic complex was active[80] southwest of Cerro Blanco[93] in the form of several stratovolcanoes[17] that produced the Cordillera de San Buenaventura;[94] afterwards came a two-million year long hiatus.

[17] The former are particularly represented east of Cerro Blanco and go back in part to the Precambrian, the latter occur mainly west and consist of Ordovician volcano-sedimentary units.

[101] Local tectonic structures[102] such as borders between crustal domains[103] and northeast-southwest trending faults might control the position of volcanic vents.

[109] Minerals encountered in the volcanic rocks include biotite, feldspar, ilmenite, magnetite quartz, less commonly amphibole, clinopyroxene, orthopyroxene, and rarely apatite, allanite-epidote, muscovite, titanite and zircon.

[110] Fumarolic alteration on the caldera ground has produced alunite, boehmite and kaolinite and deposited opal, quartz and silica.

[101] The magmatic system spans the entire thickness of the crust;[88] the rhyolites are stored in a magma chamber at about 2.5 kilometres (1.6 mi) depth.

[57] It is bushy and relatively sparse, with thicker plant growth found at hot springs[116] and in the craters where humid soils occur, perhaps wetted by ascending vapour.

[130] The oldest[l] volcanic rock formation related to Cerro Blanco is the over 750,000 years old so-called "Cortaderas Synthem".

The volcano-tectonic depression northeast of Cerro Blanco[37] or the Pie de San Buenaventura and El Niño scarps have been proposed as a source.

[98][99] As with the Cortaderas Synthem, this ignimbrite was produced by a boiling-over vent and the pyroclastic flows[n] lacked the intensity to override local topography.

[149] Sulfur oxide gases from recent activity at Cerro Blanco may have degraded rock paintings in the Salamanca cave, 70 kilometres (43 mi) south of the volcano.

[152] Deposits from this lava dome-forming episode consist of blocks which sometimes exceed sizes of 1 metre (3 ft 3 in) embedded within ash and lapilli.

They reached distances of 35 kilometres (22 mi) from Cerro Blanco[163] and while many of their up to 30-metre (98 ft) thick deposits are heavily eroded well-exposed outcrops occur south of the volcano at Las Papas.

[152] At Cueva Abra del Toro in northeastern Catamarca Province,[173] rodents disappeared after the eruption and there was a change in human activity.

[174] The eruptions of Cerro Blanco may – together with more local seismic activity – be responsible for the low population density of the Fiambalá region, Chaschuil valley and western Tinogasta Department during the Archaic period between 10,000 and 3,000 years ago.

Past intense hydrothermal activity appears to have emplaced silicic material[s] up to 40 centimetres (16 in) thick,[111] and steam explosions took place within the caldera.

[185] The geothermal system appears to consist of an aquifer hosted within pre-volcano rocks and heated by a magma chamber from below, with the Cerro Blanco ignimbrites acting as an effective seal.

[184] Supporting the effectiveness of the seal, total emissions of carbon dioxide exceed 180 kilograms per day (2.1 g/s) but are considerably lower than at other active geothermal systems of the Andes.

[36] Rhyolitic caldera systems like Cerro Blanco can produce large eruptions separated by short time intervals.

[81] Cerro Blanco received attention from scientists after satellite images in the early 21st century observed deflation of the caldera.