Английская Википедия:Cerro Blanco (volcano)

Cerro Blanco (Шаблон:IPA-es, "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 Шаблон:Convert in a depression. The caldera is associated with a less well-defined caldera to the south and several lava domes.

The caldera has been active for the last eight million years, and eruptions have created several ignimbrites.Шаблон:Efn An eruption occurred 73,000 years ago and formed the Campo de la Piedra Pómez ignimbrite layer. 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. About Шаблон:Convert of tephra Шаблон:Efn were erupted then. The volcano has been dormant since then with some deformation and geothermal activity. A major future eruption would put nearby communities to the south at risk.

The volcano is also known for giant ripple marks that have formed on its ignimbrite fields. Persistent wind action on the ground has shifted gravel and sand, forming wave-like structures. These ripple marks have heights up to Шаблон:Convert and are separated by distances up to Шаблон:Convert. These ripple marks are among the largest on Earth and have been compared to Martian ripple marks by geologists.

Geography and geomorphology

The volcano lies at the southern margin of the Argentine Puna,Шаблон:Efn Шаблон:Sfn on the border between the Antofagasta de la Sierra Department and the Tinogasta Department Шаблон:Sfn in the Catamarca Province of Argentina.Шаблон:Sfn Trails run through the area,Шаблон:Sfn and there are abandoned mining operations.Шаблон:Sfn Provincial Route 34 (Catamarca) between Fiambalá and Antofagasta de la Sierra runs past Cerro Blanco.Шаблон:Sfn The volcano is sometimes known as Cerro Blanco, meaning "white hill" in Spanish, and sometimes as Robledo;Шаблон:Sfn the Smithsonian Institution uses the latter name.Шаблон:Sfn

Calderas and lava domes

Cerro Blanco lies at an elevation of Шаблон:Convert and consists of four nested calderasШаблон:Sfn with discontinuous borders,Шаблон:Sfn fallout deposits, lava domes Шаблон:Sfn and pyroclastic deposits.Шаблон:Sfn The two inconspicuous El Niño and Pie de San Buenaventura calderas are nested in the northern part of the complexШаблон:Sfn and form a Шаблон:Convert wide depression;Шаблон:Sfn El Niño is sometimes referred to as a scarp.Шаблон:Sfn Only their northern margins are recognisable in satellite images; their southern parts are filled with block-and-ash flows from the southern calderas. The southern calderas are the Robledo and Cerro Blanco calderas, which form a southeast-northwest trending pair.Шаблон:Sfn Alternative interpretations consider the Pie de San Buenaventura, Robledo and Cerro Blanco calderas as one Шаблон:Convert caldera,Шаблон:Sfn Шаблон:Sfn that the Robledo and Cerro Blanco calderas are one systemШаблон:Sfn or envisage the existence of only three calderas.Шаблон:Sfn

The Cerro Blanco caldera is about Шаблон:Convert wide and its walls are up to Шаблон:Convert high.^[1]Шаблон:Sfn They are formed by ignimbrite breccia, ignimbrites and lava domes cut by the caldera margins.Шаблон:Sfn The caldera floor is almost entirely covered by block-and-ash flows, apart from an area where hydrothermal activity has left white sinter deposits.Шаблон:Sfn A slight circular uplift on the caldera floor may be a cryptodome.Шаблон:Efn Шаблон:Sfn

The caldera has an almost perfectly circular outline with the exception of the southwestern marginШаблон:Sfn which is cut by a Шаблон:Convert wide lava dome.Шаблон:Sfn This dome is also known as Cerro BlancoШаблон:Sfn or Cerro Blanco del Robledo^[1] and reaches a height of Шаблон:Convert above sea level.Шаблон:Sfn Three additional lava domes surround this dome, and an explosion crater lies to its southwest. West of this craterШаблон:Sfn there are three pinkish lava domesШаблон:Sfn lined up in west-southwest direction away from the main dome;Шаблон:Sfn these are surrounded by pyroclastic cones Шаблон:Sfn and depressions.Шаблон:Sfn

Owing to erosion, the Robledo calderaШаблон:Sfn is less well defined than the Cerro Blanco caldera.Шаблон:Sfn A site southeast of the Robledo caldera is known as Robledo.Шаблон:Sfn South of the Robledo caldera lies the Portezuelo de Robledo mountain pass,Шаблон:Sfn the south-eastward trending El Médano plainШаблон:Sfn and the Robledo valley.Шаблон:Sfn

About Шаблон:Convert northeast of Cerro Blanco lies a Шаблон:Convert wide and Шаблон:Convert deep vent known as El EscondidoШаблон:Sfn or El Oculto.Шаблон:Sfn It does not have a strong topographic expression but is conspicuous on satellite images as a semi-circular patch of darker material.Шаблон:Sfn Gravimetric analysis has found a number of gravity anomalies around the caldera.Шаблон:Sfn

Surrounding terrain

The terrain northeast-east from Cerro Blanco is covered by its ignimbrites and by Plinian fallout depositsШаблон:Sfn which radiate away from the calderas.Шаблон:Sfn Cerro Blanco lies at the southwestern end of the Carachipampa valley,Шаблон:Sfn a volcano-tectonic depression flanked by normal faults which extends to Carachipampa. This depression appears to have formed in response to north-south tectonic extension of the PunaШаблон:Sfn and is covered by volcanic deposits from Cerro Blanco.Шаблон:Sfn These volcanic deposits form the "Campo de Pedra Pomez"Шаблон:Sfn and extend Шаблон:Convert away from the volcano.Шаблон:Sfn To the north, the El Niño scarpШаблон:Sfn of the El Niño calderaШаблон:Sfn separates the Cerro Blanco caldera from the Purulla valley.Шаблон:Sfn

Other valleys are the Purulla valley northwest from Cerro Blanco and Incahuasi due north; all three contain both volcanic deposits from Cerro Blanco and salt flats Шаблон:Sfn or lakes.Шаблон:Sfn In the Incahuasi valley an ignimbrite also known as the "white ignimbrite" reaches a distance of over Шаблон:Convert.Шаблон:Sfn Wind has carved Шаблон:Convert deep channels into the ignimbrites.Шаблон:Sfn

Aeolian landscapes

One of the most spectacular aeolian Шаблон:Efn landscapes is found at Cerro Blanco,Шаблон:Sfn where large wind-formed ripple marks occur.Шаблон:Sfn These ripples cover Cerro Blanco ignimbritesШаблон:Sfn and reach heights of Шаблон:Convert and wavelengths of Шаблон:Convert, making them the largest ripples known on Earth and comparable to similar ripple fields on Mars.Шаблон:Sfn Шаблон:Sfn Wind-driven erosion of ignimbritesШаблон:Efn has generated the ripples,^[2] which consist of gravel, pebbles and sandШаблон:Sfn and are covered with gravel.Шаблон:Sfn Smaller gravelly ripples lie atop the larger ripples and troughsШаблон:Sfn and there are intermediate sized forms (Шаблон:Convert high); they may be precursors to the large ripples and make up most of the ripples in the fields.Шаблон:Sfn Their wind-driven movement is fast enough that trails abandoned four years before are already partly covered with them.Шаблон:Sfn

The ripple marks cover areas of about Шаблон:Convert or Шаблон:Convert in the Carachipampa and Шаблон:Convert or Шаблон:Convert in the PurullaШаблон:Efn valley. A field of large ripples covers an area of Шаблон:Convert in the Purulla valleyШаблон:Sfn Шаблон:Sfn and is accompanied by yardangs; this field is also the place where the largest ripples occur.Шаблон:Sfn

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 Шаблон:Sfn or creep-like movement when pumice fragments and sand are lifted from the ground by wind and fall back.Шаблон:Sfn The latter view envisages that undulating terrain triggers the development of ripples through the accumulation of gravel and sand at such undulations.Шаблон:Sfn Their formation appears to be influenced by whether the rock material available can be moved by windШаблон:Sfn while a role of the bedrock structure or the size of the material is controversial.^[2]Шаблон:Sfn

Photo of white wave-like rocks

Campo de Piedra Pómez yardangs

Wind has also formed demoisellesШаблон:Efn and yardangs in the ignimbrites.Шаблон:Sfn These are particularly well expressed in the Campo de Piedra Pomez areaШаблон:Sfn Шаблон:Efn southeast of the Carachipampa valley,Шаблон:Sfn a Шаблон:Convert area where yardangs, hoodoos and wind-exposed cliffs create a majestic landscape. The structures reach widths of Шаблон:Convert Шаблон:Sfn and heights of Шаблон:Convert Шаблон:Sfn and form an array-like assembly.Шаблон:Sfn They have fluted surfaces.Шаблон:Sfn The yardangs appear to form beginning from either a pre-existing topographic elevationШаблон:Sfn or a fumarolic vent where the rock has been hardened, and eventually develop through a series of early, intermediate and late yardang formsШаблон:Sfn as wind and wind-transported particles erode the rocks.Шаблон:Sfn Their layout may be influenced by regional tectonics, pre-existent topography and the patterns formed by the ignimbrite deposits.Шаблон:Sfn Exposed rocks are often covered with brown, orange or beige desert varnish Шаблон:Sfn and sometimes are oversteepened and collapse.Шаблон:Sfn

Bedrock ridges are cut into ignimbrites of the Incahuasi valley.Шаблон:Sfn This terrain gradually leads over into the megaripple-covered surface through an increased gravel cover. The development of these megaripples appears to have been influenced by the underlying bedrock ridgesШаблон:Sfn which move along with the overlying ripples. These bedrock ridges are formed through erosion by wind and by wind-transported particles,Шаблон:Sfn it is not clear how they are then exposed from the ripples.Шаблон:Sfn Additional aeolian landforms in the region are known and include ventifacts and so-called "aeolian rat tails";Шаблон:Sfn these are small structures which form when erosion-resistant rock fragments slow wind erosion in their lee, thus leaving a tail-like area where less rock is eroded.Шаблон:Sfn Wind streaks occur in groups.Шаблон:Sfn

The Campo de Piedra Pómez makes up the Шаблон:Ill, a protected area of Catamarca Province.^[3] It was among the finalists in the "Seven Wonders of Argentina" contest^[4] but was not selected when the results were announced in 2019.^[5]

Regional

Cerro Blanco is located south of the southern end of the Filo ColoradoШаблон:Sfn/Los Colorados mountain rangeШаблон:Sfn and at the eastern end of the Шаблон:Interlanguage link.Шаблон:Sfn The Cordillera de San Buenaventura marks the southern margin of the PunaШаблон:Sfn and extends west-southwestwards from Cerro Blanco to the volcanoes San Francisco and Falso Azufre Шаблон:Sfn and the Paso de San Francisco.Шаблон:Sfn It marks the boundary between the steep subduction to the north from the shallower subduction to the south.Шаблон:Sfn

A series of andesitic to dacitic stratovolcanoes ranging in age from 1 to 6 million years old make up the Cordillera de San Buenaventura,Шаблон:Sfn Шаблон:Sfn and Quaternary basaltic volcanoes are dispersed over the wider region.Шаблон:Sfn In the surroundings of Cerro Blanco lies the Cueros de Purulla volcano Шаблон:Convert north and the Nevado Tres Cruces-El Solo-Ojos del Salado complex farther west.Шаблон:Sfn

Geology

Subduction of the Nazca Plate beneath the South America Plate occurs in the Peru-Chile Trench at a rate of Шаблон:Convert. It is responsible for the volcanism in the Andes, which is localised in three volcanic zones known as the Northern Volcanic Zone, Central Volcanic Zone and Southern Volcanic Zone.Шаблон:Sfn Cerro Blanco is part of the Andean Central Volcanic Zone (CVZ), and one of its southernmost volcanoes.Шаблон:Sfn The CVZ is sparsely inhabited and recent volcanic activity is only poorly recorded;Шаблон:Sfn Lascar is the only regularly active volcano there.^[6]

The CVZ extends over the Altiplano-PunaШаблон:Sfn where calc-alkaline volcanism has been ongoing since the Miocene.Шаблон:Sfn Characteristic for the CVZ are the large fields of ignimbritic volcanism and associated calderas, chiefly in the Altiplano-Puna volcanic complex. In the southern part of the CVZ such volcanic systems are usually small and are poorly studied.Шаблон:Sfn During the Neogene, volcanism commenced in the Maricunga belt and eventually shifted to its present-day location in the Western Cordillera.Шаблон:Sfn Tectonic processes also took place, such as two phases of east-west compression; the first was in the middle Miocene and the second began 7 million years ago.Шаблон:Sfn

Volcanism in the southern Puna region initiated about 8 million years ago and took place in several stages, which were characterised by the emplacement of lava domes and of ignimbrites such as the 4.0–3.7 million year old Laguna Amarga-Laguna Verde ignimbrites. Some of the domes are located close to the border with Chile in the Ojos del Salado and Nevado Tres Cruces area. Later there also were mafic eruptions, which generated lava flows in the Carachipampa and Laguna de Purulla area.Шаблон:Sfn The late mafic eruption products and the Cerro Blanco volcanics are geologically classified as making up the "Purulla Supersynthem".Шаблон:Sfn From the Miocene to the Pliocene the La Hoyada volcanic complex was activeШаблон:Sfn southwest of Cerro BlancoШаблон:Sfn in the form of several stratovolcanoesШаблон:Sfn that produced the Cordillera de San Buenaventura;Шаблон:Sfn afterwards came a two-million year long hiatus.Шаблон:Sfn Cerro Blanco overlies this volcanic complexШаблон:Sfn and outcrops of La Hoyada are found insideШаблон:Sfn and around the calderas;Шаблон:Sfn sometimes it is considered part of La Hoyada.Шаблон:Sfn Шаблон:Sfn

The basement is formed by metamorphic, sedimentary and volcanic rocks of Neoproterozoic to Paleogene age.Шаблон:Sfn 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. Both are intruded by granitoids and mafic and ultramafic rocks. Permian sediments and Paleogene rocks complete the nonvolcanic geology.Шаблон:Sfn Local tectonic structuresШаблон:Sfn such as borders between crustal domainsШаблон:Sfn and northeast-southwest trending faults might control the position of volcanic vents.Шаблон:Sfn Tectonic processes may also be responsible for the elliptic shape of the Cerro Blanco caldera.Шаблон:Sfn There is evidence of intense earthquakes during the QuaternaryШаблон:Sfn and some faults such as the El Peñón Fault have been recently active.Шаблон:Sfn

Composition

Most of the volcanic rocks found at Cerro Blanco are rhyolites Шаблон:Sfn Шаблон:Sfn and define two suites of calc-alkaline rocks.Шаблон:Sfn 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.Шаблон:Sfn Fumarolic alteration on the caldera ground has produced alunite, boehmite and kaolinite and deposited opal, quartz and silica.Шаблон:Sfn

Magma temperatures have been estimated to range between Шаблон:Convert. The rhyolites erupted at Cerro Blanco appear to form from andesite magmas, through processes such as fractional crystallisation and the absorption of crustal materials.Шаблон:Sfn Шаблон:Sfn The rhyolites are stored in a magma chamber at about Шаблон:Convert depth.Шаблон:Sfn

Climate and vegetation

Mean temperatures in the region are below Шаблон:Convert but daily temperature fluctuations can reach Шаблон:Convert and insolation is intense.Шаблон:Sfn Vegetation in the region is classified as a high desert vegetation.Шаблон:Sfn It is bushy and relatively sparse, with thicker plant growth found at hot springsШаблон:Sfn and in the craters where humid soils occur, perhaps wetted by ascending vapour.Шаблон:Sfn

Annual precipitation is less than Шаблон:Convert^[7] and moisture in the region comes from the Amazon in the east.Шаблон:Sfn This aridity is a consequence of the region being within the Andean Arid Diagonal, which separates the northern monsoon precipitation regime from the southern westerlies precipitation regime,Шаблон:Sfn and the rain shadow of the Andes, which prevents eastern moisture from reaching the area.Шаблон:Sfn The climate of the region has been arid since the Miocene but fluctuations in humidity occurred especially during the last glacial Шаблон:Sfn and between 9,000–5,000 years ago when climate was wetter.Шаблон:Sfn The aridity results in a good preservation of volcanic products.Шаблон:Sfn

Strong winds blow at Cerro Blanco.Шаблон:Sfn Average windspeeds are unknownШаблон:Sfn owing to the lack of measurements in the thinly populated regionШаблон:Sfn and there are contrasting reports on wind speed extremesШаблон:Sfn but gusts of Шаблон:Convert have been recorded in July^[2] and wind speeds in early December 2010 regularly exceeded Шаблон:Convert.Шаблон:Sfn Winds blow mainly from the northwest,Шаблон:Sfn and have been stable in that orientation for the past 2 million years. This favoured the development of extensive aeolian landforms Шаблон:Sfn although winds coming from other directions also play a role.Шаблон:Sfn Thermal winds are generated by differential heating of surfaces in the region,Шаблон:Sfn and diurnal winds are controlled by the day-night cycle.Шаблон:Sfn Winds kick up pyroclastic material, generating dust storms Шаблон:Sfn which remove dust and sand from the area. Some of the dust is carried out into the Pampa, where it forms loess deposits,Шаблон:Sfn and dust deposition at Cerro Blanco can quickly obscure vehicle tracks.Шаблон:Sfn Dust devils have been observed.^[8]

Eruption history

The Cerro Blanco volcanic system has been active during the Pleistocene and Holocene.Шаблон:Sfn The oldestШаблон:Efn volcanic rock formation related to Cerro Blanco is the over 750,000 years old so-called "Cortaderas Synthem". Its outcrops are limited to the Laguna Carachipampa area. It consists of two ignimbrites, the Barranca Blanca Ignimbrite and the Carachi Ignimbrite, which erupted a long time apart. The former is a massive, white, unwelded ignimbrite, the latter is massive, rose-coloured and weakly welded. They contain pumice and fragments of extraneous rockШаблон:Sfn and consist of rhyodacite unlike later units.Шаблон:Sfn These ignimbrites, whose chronological relation to each other is unknown, were probably produced by "boil-over" of a volcanic vent rather than by an eruption column.Шаблон:Sfn Their exact source vent is unknown.Шаблон:Sfn

The Campo de la Piedra PómezШаблон:Efn Ignimbrite covers an area of about Шаблон:Convert north of Cerro Blanco and has a volume of about Шаблон:Convert. It was emplaced in two units a short time from each other. They both contain pumice and fragments of country rock, similar to the Cortaderas Synthem. The most reliable radiometrically obtained dates for this ignimbrite indicate an age of 73,000 years;Шаблон:Sfn previous estimates of their age were 560,000 ± 110,000 and 440,000 ± 10,000 years before present.Шаблон:Sfn The 73,000 age is considered to be more reliableШаблон:Sfn but in 2022 an age of 54,600 ± 600 years was proposed for this eruption.Шаблон:Sfn The eruption reached level 6 on the Volcanic Explosivity Index Шаблон:Sfn and is also known as the first cycle ignimbrite.Шаблон:Sfn The eruption has been described as the largest caldera collapse at Cerro BlancoШаблон:Sfn but the source vent for this eruption has not been found, and there is no agreement whether the Robledo Caldera is the source. The volcano-tectonic depression northeast of Cerro BlancoШаблон:Sfn or the Pie de San Buenaventura and El Niño scarps have been proposed as a source.Шаблон:Sfn Шаблон:Sfn As with the Cortaderas Synthem, this ignimbrite was produced by a boiling-over vent and the pyroclastic flows Шаблон:Efn lacked the intensity to override local topography. It is possible that the eruption proceeded in two phases, with a magmatic reinvigoration of the system between the two.Шаблон:Sfn After the ignimbrite cooled and solidified, cracks formed in the rocks and were later eroded by wind.Шаблон:Sfn The Campo de la Piedra Pómez Ignimbrite crops out mainly on the southeastern and northwestern sides of the Carachipampa valley, as between these two outcrops it was buried by the later Cerro Blanco ignimbrite; other outcrops lie in the Incahuasi and Purulla valleys.Шаблон:Sfn The Robledo and Pie de San Buenaventura calderas were formed during the early activity.Шаблон:Sfn Шаблон:Sfn

A 22,700–20,900 years old tephra deposit in a lake of northwestern Argentina has been attributed to Cerro Blanco.^[9] The volcano appears to have erupted repeatedly during the Holocene.Шаблон:Sfn Шаблон:Sfn Explosive eruptions took place between 8,830 ± 60 and 5,480 ± 40 years before present and deposited tephraШаблон:Sfn and ignimbrites south of Cerro Blanco.Шаблон:Sfn Two tephra deposits in the Calchaquí valley have been attributed to Cerro Blanco; one of these is probably linked to the 4.2 ka eruption.^[10] Sulfur oxide gases from recent activity at Cerro Blanco may have degraded rock paintings in the Salamanca cave, Шаблон:Convert south of the volcano.^[11]

4.2 ka eruption

A large eruption occurred approximately 4,200 years ago. Block-and-ash flow deposits (classified as "CBШаблон:Sub"Шаблон:Efn) found around the caldera have been interpreted as indicating that a lava dome was erupted prior to the caldera collapse at Cerro Blanco, although it is not clear by how much this eruption predates the main eruption.Шаблон:Sfn Deposits from this lava dome-forming episode consist of blocks which sometimes exceed sizes of Шаблон:Convert embedded within ash and lapilli.Шаблон:Sfn

A vent opened up, presumably on the southwestern side of the future caldera, and generated a 27 km (17 mi)-high eruption column.Шаблон:Sfn Fissure vents may have opened as well.Шаблон:Sfn After an initial, unstable phase during which alternating layers of lapilli and volcanic ash (unit "CBШаблон:Sub1") fell outШаблон:Sfn and covered the previous topography,Шаблон:Sfn a more steady column deposited thicker rhyolitic tephra layers (unit "CBШаблон:Sub2").Шаблон:Sfn At this time, a change in rock composition occurred, perhaps due to new magma entering the magma chamber.Шаблон:Sfn

Windy conditions dispersed most of the tephra to the east-southeast,Шаблон:Sfn covering a surface of about Шаблон:Convert with about Шаблон:Convert of tephra.Шаблон:Sfn The thickness of the tephra decreasesШаблон:Efn eastwards away from Cerro BlancoШаблон:Sfn and reaches a thickness of about Шаблон:Convert Шаблон:Sfn Шаблон:Convert away from Cerro Blanco in Santiago del Estero.Шаблон:Sfn The tephra deposits in the Valles Calchaquies and Tafi del Valle area are known as mid-Holocene ash, Ash C, Buey Muerto ash, and V1 ash layer,Шаблон:Sfn and it has been found northeast of Antofagasta de la Sierra.^[12] The tephra from the 4.2 ka eruption has been used as a chronological marker in the region.Шаблон:Sfn Modelling suggests the tephra might have reached Brazil and Paraguay farther east.Шаблон:Sfn Close to the vent, tephra fallout was emplaced on the Cordillera de San Buenaventura.Шаблон:Sfn Some of the tephra deposits close to the caldera have been buried by sediments, or soil development has set in.Шаблон:Sfn Wind removed the volcanic ash, leaving block and lapilli sized pebbles that cover most of the deposits; in some places dunes have formed from pebbles.Шаблон:Sfn

Pyroclastic flows also formed, perhaps through instability of the eruption column (unit "CBШаблон:Sub3"),Шаблон:Sfn and spread away from the volcano through surrounding valleys. They reached distances of Шаблон:Convert from Cerro BlancoШаблон:Sfn and while many of their up to Шаблон:Convert thick deposits are heavily eroded well-exposed outcrops occur south of the volcano at Las Papas. They consist of pumice fragments of varying sizes embedded within ash,Шаблон:Sfn as well as country rock that was torn up and embedded in the flows.Шаблон:Sfn In the south, pyroclastic flows descending valleys partially overflowed their margins to flood adjacent valleysШаблон:Sfn and reached the Шаблон:Interlanguage link.Шаблон:Sfn North-westward and north-eastward flowing ignimbrites generated ignimbrite fans in the Purulla and Carachipampa valleys, respectively.Шаблон:Sfn

The deposits from this event are also known as Cerro Blanco Ignimbrite, as Ignimbrite of the second cycle or El Médano or Purulla Ignimbrite.Шаблон:Sfn Formerly these were dated to be 12,000 and 22,000 years old, respectively, and related to the Cerro Blanco and (potentially) Robledo calderas.Шаблон:Sfn Cerro Blanco is considered to be the youngest caldera of the Central Andes.Шаблон:Sfn

With a volume of Шаблон:Convert of tephra,Шаблон:Efn^[13] the 4.2 ka eruption has been tentativelyШаблон:Sfn classified as 7 on the Volcanic Explosivity Index,Шаблон:Sfn making it comparable to the largest known Holocene volcanic eruptions.Шаблон:Sfn It is the largest known Holocene eruption in the Central Andes^[1] and of the Central Volcanic Zone,^[14] larger than the 1600 Huaynaputina eruption, the largest historical eruption of the Central Volcanic Zone.Шаблон:Sfn Most of the erupted volume was ejected by the eruption column, while only about Шаблон:Convert ended up in pyroclastic flows.Шаблон:Sfn Caldera collapse occurred during the course of the eruption, generating the unusually small (for the size of the eruption) Cerro Blanco calderaШаблон:Sfn through a probably irregular collapse.Шаблон:Sfn

Some authors have postulated that mid-Holocene eruptions of Cerro Blanco impacted human communities in the region.Шаблон:Sfn Tephra deposits in the Formative Period archaeological site of Palo Blanco in the Bolsón de Fimabalá have been attributed to Cerro Blanco,Шаблон:Sfn as is a tephra layer in an archaeological site close to Antofagasta de la Sierra.Шаблон:Sfn At Cueva Abra del Toro in northeastern Catamarca Province,Шаблон:Sfn rodents disappeared after the eruption and there was a change in human activity.Шаблон:Sfn 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.Шаблон:Sfn The 4.2 kiloyear climatic event occurred at the same time; it may be in some way related to the Cerro Blanco eruption.Шаблон:Sfn

Post–4.2 ka activity

After the caldera-forming eruption, renewed effusive eruptions generated the lava domes southwest of and on the margin of the Cerro Blanco calderaШаблон:Sfn and phreatic/phreatomagmatic activity occurred.Шаблон:Sfn The current topography of Cerro Blanco is formed by the deposits from this stage,Шаблон:Sfn whose activity was influenced by intersecting fault systemsШаблон:Sfn including a northeast-southwest trending fault that controls the position of lava domes outside and fumarolic vents within the caldera.Шаблон:Sfn

It's not clear how long after the 4.2 ka eruption this activity occurred, but it has been grouped as the "CBШаблон:Sub" unit (the domes are classified as "CBШаблон:Sub1"). This activity also generated block-and-ash deposits (unit "CBШаблон:Sub2") on the caldera floor.Шаблон:Sfn The domes are of rhyolitic composition, the block-and-ash deposits consist of ash and lapilliШаблон:Sfn and appear to have formed when domes collapsed.Шаблон:Sfn As lava domes grow, they tend to become unstable as their vertical extent increases until they collapse. Additionally, internally generated explosions appear to have occurred at Cerro Blanco as lava domes grew and sometimes completely destroyed the domes.Шаблон:Sfn

Present-day status

NoШаблон:Efn historical eruptions have been observed or recorded at Cerro Blanco,Шаблон:Sfn but various indicators imply that it is still active.Шаблон:Sfn In 2007–2009, seismic swarms were recorded at less than Шаблон:Convert depth.Шаблон:Sfn

Geothermal activity occurs at Cerro Blanco, and manifests itself on the caldera floor through hot ground, fumaroles,Шаблон:Sfn diffuse degassing of Шаблон:Chem,Шаблон:Sfn and reportedly hot springs Шаблон:Sfn and mud volcanoes;Шаблон:Sfn phreatic eruptions may have occurred in the past.Шаблон:Sfn Fumaroles release mainly carbon dioxide and water vapour with smaller amounts of hydrogen, hydrogen sulfide and methane;Шаблон:Sfn they reach temperatures of Шаблон:Convert while temperatures of Шаблон:Convert have been reported for the hot ground. Past intense hydrothermal activity appears to have emplaced silicic materialШаблон:Efn up to Шаблон:Convert thick,Шаблон:Sfn and steam explosions took place within the caldera.Шаблон:Sfn Active fumaroles and clay cones formed by fumarolic activity are also found in the phreatic crater.Шаблон:Sfn 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.Шаблон:Sfn Supporting the effectiveness of the seal, total emissions of carbon dioxide exceed Шаблон:Convert but are considerably lower than at other active geothermal systems of the Andes.Шаблон:Sfn It has been prospected for possible geothermal power generation.Шаблон:Sfn Шаблон:Sfn

A second geothermal field related to Cerro Blanco is located south of the volcano and is known as Los HornitosШаблон:Sfn or Terma Los Hornos,Шаблон:Sfn in the area of the Los Hornos and Las Vizcachas creeks.Шаблон:Sfn It is located in a ravine and consists of three clusters of bubbling pools, hot springs, up to Шаблон:Convert high travertine domes that discharge water and extinct geyser cones;Шаблон:Sfn these cones give the field its name and some of them were active until 2000.Шаблон:Sfn Water temperatures range between Шаблон:Convert,Шаблон:Sfn the vents are settled by extremophilic organisms.Шаблон:Sfn The springs deposit travertine,Шаблон:Efn Шаблон:Sfn forming cascades, dams, pools and terraces of varying size,Шаблон:Sfn as well as pebbles.Шаблон:Sfn Fossil travertine deposits are also found and form a carbonate rock plateauШаблон:Sfn generated by waters rising from a fissure.Шаблон:Sfn The Los Hornos system has been interpreted as a leak from the Cerro Blanco geothermal system,Шаблон:Sfn and south-westward trending fault systems might connect it to the Cerro Blanco magmatic system.Шаблон:Sfn

Deformation and hazards

Subsidence at a rate of Шаблон:Convert has been noted at the caldera since 1992Шаблон:Sfn in InSAR images. The rate of subsidence was originally believed to have decreased from over Шаблон:Convert between 1992 and 1997 to less than Шаблон:Convert between 1996 and 2000Шаблон:Sfn and ceased after 2000.Шаблон:Sfn Later measurements found that the subsidence rate instead had been steady between 1992 and 2011 with Шаблон:Convert, but with a faster phase between 1992 and 1997^[15] and a slower phase between 2014 and 2020 of Шаблон:Convert,Шаблон:Sfn and the location the subsidence is centred on has changed over time.Шаблон:Sfn The subsidence occurs at Шаблон:Convert depthШаблон:Sfn and has been related to either a cooling magmatic system, changes in the hydrothermal systemШаблон:Sfn Шаблон:Sfn or to subsidence that followed the 4.2 ka eruption and is still ongoing.^[6] Uplift in the area surrounding the caldera has also been identified.Шаблон:Sfn

The Argentinian Mining and Geological Service has ranked Cerro Blanco eight in its scale of hazardous volcanoes in Argentina.Шаблон:Sfn Rhyolitic caldera systems like Cerro Blanco can produce large eruptions separated by short time intervals. Future activity might involve either a "boiling-over" of pyroclastic flows or Plinian eruptions. Given that the region is sparsely inhabited, the primary effects of a new eruption at Cerro Blanco would come from the eruption column, which could spread tephra eastwards and impact air traffic there. Also, pyroclastic flows could through narrow valleys reach the Bolsón de Fiambalá valley Шаблон:Convert south of Cerro Blanco, where many people live.Шаблон:Sfn

Research history

Research in the region commenced in the 19th century and was mainly concentrated on mining.Шаблон:Sfn Cerro Blanco received attention from scientists after satellite images in the early 21st century observed deflation of the caldera.Шаблон:Sfn A number of Holocene tephra layers have been identified in the region, but linking these to specific eruptions has been difficultШаблон:Sfn until 2008–2010 when some of these were linked to the Cerro Blanco vent.Шаблон:Sfn Scientific interest rose in the 2010s due to the discovery of the large 4.2 ka eruption.Шаблон:Sfn

Notes

Шаблон:Notelist

References

Шаблон:Reflist

Sources

Шаблон:Refbegin

Шаблон:Refend

External links

Шаблон:Commons category

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