| Tacora | |
|---|---|
 Tacora in 2004 | |
| Highest point | |
| Elevation | 5,980 m (19,620 ft)[1] |
| Prominence | 1,721 m (5,646 ft)[2] |
| Parent peak | Nevado Sajama |
| Listing | Ultra |
| Coordinates | 17°43′14″S69°46′22″W / 17.72056°S 69.77278°W /-17.72056; -69.77278 |
| Geography | |
  Tacora | |
| Parent range | Andes |
| Geology | |
| Mountain type | Stratovolcano |
| Volcanic zone | Central Volcanic Zone |
| Last eruption | Unknown |
Tacora is astratovolcano located in theAndes of theArica y Parinacota Region ofChile. Near the border withPeru, it is one of the northernmost volcanoes of Chile. It is part of theCentral Volcanic Zone in Chile, one of the four volcanic belts of the Andes. The Central Volcanic Zone has several of the highest volcanoes in the world. Tacora itself is astratovolcano with acaldera and acrater. The youngestradiometric age is 50,000 years ago and it is heavily eroded byglacial activity.
Volcanism in the Central Volcanic Zone results from thesubduction of theNazca Plate beneath theSouth America Plate. Tacora is constructed on the so-called "Arica Altiplano" and is part of a north–south alignment of volcanoes. Tacora itself has uncertain reports of historical eruptions and there are activefumaroles.
The fumarolic activity has resulted in the emplacement of substantial deposits ofsulfur, which were already mentioned centuries ago. Towards the latter 19th century, systematicmining of the sulfur deposits of Tacora occurred and substantial mining infrastructure was constructed on the mountain.
Tacora lies in theArica y Parinacota Region of Chile, about 100 kilometres (62 mi) northeast ofArica. It is among the northernmost volcanoes of Chile[3] and poorly known.[4]
Tacora is part of theCentral Volcanic Zone,[4] one out of several volcanic belts of the Andes.[3] The Central Volcanic Zone is one of the world's major volcanic provinces and features both a high density of volcanoes and some of the tallest volcanic edifices in the world.[5] Volcanoes in the Central Volcanic Zone includeSabancaya,El Misti andUbinas in Peru and Tacora,Isluga,Irruputuncu,Ollague,San Pedro,Putana,Alitar,Lascar andLastarria in Chile, Bolivia and Argentina;[3] there are about 34 volcanoes in the Chilean portion of the Central Volcanic Zone alone.[6] Of these Lascar is considered to be the most active, with a large eruption in 1993.[7] Aside from volcanoes, the Central Volcanic Zone also featuresgeothermal fields such asEl Tatio.[4]
The volcano is a 5,980 metres (19,620 ft) high[8][9] cone with a summitcaldera that opens northwest and a 500-metre (1,600 ft) widecrater below the summit[3] within the calderascarp.[10] Steeplava flows form the bulk of the edifice,[11] along withlava domes andpyroclastic material,[12] and rise about 1.7 kilometres (1.1 mi) above the surrounding terrain.[8] The edifice is heavilyeroded[13] with about 32 metres (105 ft) of rocks gone[14] but still has a circular shape.[13] There are traces of asector collapse scar and of the resulting debris avalanche on the southeastern flank.[12]
According to some reportsglaciers occur within the caldera at elevations above 5,500 metres (18,000 ft),[3] while other reports indicate the absence of perennial snow on the mountain.[15] Glacial valleys andmoraines have been recognized on the eastern, southeastern and southern slopes of the volcano,[3] andcirques have been found at 5,000 metres (16,000 ft) elevation. These landforms suggest that the mountain was formerly glaciated.[15] Three sets of moraines have been described, one at 4,400 metres (14,400 ft) elevation possibly linked to thelast glacial maximum, an older one at 4,500 metres (14,800 ft) elevation and a third at 4,900 metres (16,100 ft) elevation which may have formed during theLittle Ice Age;[13] moraines reach thicknesses of 200 metres (660 ft).[8] There is an additional set of moraines at 4,350–4,300 metres (14,270–14,110 ft) elevation that has been correlated to pre-last glacial maximum glaciations,[16] as well as traces of ice cored moraines androck glaciers.[17] Some rock glaciers still exist; unlike other glacial bodies in Chile the fronts of rock glaciers on Tacora are not retreating.[18]
The mountain is an important source of water for the region.[19] The Azufre River, a major tributary of theLluta River, originates on Tacora,[20][21] and its waters are highly salty owing to their origin on the volcano.[22] The Chislluma River flows past the northeastern flank of Tacora and the Rio Caracarani past the southeastern one; finally, theMauri Canal andUchusuma Canal run along the southeastern slopes.[23]
On the western and northwestern flanks,solfataras are present[4] both in the form offumaroles and of steaming ground, and the Aguas Calientes de Tacorahot springs are located 2 kilometres (1.2 mi) southwest of the volcano.[3] Further,geyserite cones indicate thatgeysers were formerly active on the volcano.[24]Seismic tomography has been used to image both the hydrothermal systems andmagma systems of the volcano.[25] Prospecting forgeothermal power generation[26] concluded it is a "highly favourable area".[27] In 2009, the Chilean Ministry of Mining recorded bids for geothermal development at Tacora,[28] and one bid was approved by the Ministry in early 2010.[29]
Fumarole gases are dominated bywater vapour with other components includingcarbon dioxide,hydrogen chloride,hydrogen fluoride,hydrogen sulfide,nitrogen andsulfur dioxide.Hydrogen,methane and otherhydrocarbons are also common in the exhalations. The temperatures of the fumaroles reach 82–93 °C (180–199 °F)[10] and daily sulfur dioxide emissions have been estimated to be 0.01–0.02 tonnes per day (0.12–0.23 g/s) in the major fumaroles.[30]
The fumarolic gases are interpreted to originate by the evaporation of anaquifer that is saturated by solfataric components, resulting both in the exhalation of gases and the development of acid hot springs. This aquifer is mostly replenished by precipitation and to a lesser degree bymagmatic water.[31] Further, there appears to be ahydrothermal system with temperatures of 270–310 °C (518–590 °F) under the volcano that fumarolic gases pass through,[32] and amagma system between sea level and 2 kilometres (1.2 mi) of depth.[33] Overall, fumarolic gases at Tacora undergo substantial interaction with rocks and hydrothermal systems before they reach the surface.[34] A cluster ofseismic activity below the eastern flank may also be correlated to a fluid system at depth.[35]
Subduction of theNazca Plate beneath theSouth America Plate is responsible for the volcanism of the Andes. This volcanism does not occur along the entire strike of the Andes, but in three selected volcanic belts, theNorthern Volcanic Zone, theCentral Volcanic Zone and theSouthern Volcanic Zone. A fourth volcanic zone, theAustral Volcanic Zone, lies south of the Southern Volcanic Zone.[5] These volcanically active belts are separated by gaps where recent volcanism is absent and the subducting plate descends in a much shallower angle.[36]
Volcanoes of the Peruvian Central Volcanic Zone generally occur within a narrow belt and are usually associated withnormal faults.[37] Most edifices are between 1,500–3,000 metres (4,900–9,800 ft) high above their basement and consist oflava flows andpyroclastics. Old edifices are far more common in Chile than in Peru, and are especially rare in the northwestern part of Peru's volcanic zone; this may be the consequence of climatic factors or a later start of volcano-building activity in Peru.[38] About 17 volcanoes arefumarolically active in northern Chile, withigneous activity limited to about 6.[39]
The earliest volcanic activity in northern Chile occurred between 41 and 66 million years ago, and is linked to an ancientvolcanic arc.[39] Later during theMiocene two separate but partially overlapping volcanic episodes occurred, the first of which was dominated by the emplacement ofignimbrites and the second by the growthcomposite volcanoes, with vigorous activity during thePliocene andPleistocene.[40]
The basement beneath Tacora is formed by the Arica Altiplano, aformation lying at about 4,200 metres (13,800 ft) altitude that consists of various sedimentary and volcanic rocks ofPliocene toPleistocene age. Tacora together with Chupiquiña, Nevado El Fraile and Nevado La Monja forms a 10 kilometres (6.2 mi) long alignment of volcanoes that crosses into Peru and extends from south to north.[3] In addition, afault system known as the Challavientoreverse fault passes underneath the volcano; it also extends into Peru where it belongs to the active Incapuquio–Challaviento fault system.[41]
The volcano is composed ofdacite and lesser amounts ofandesite[12] in the form ofpyroclastic material andlava flows; the latter are predominantly andesitic tobasaltic andesite. Minerals contained in the lava flows arebiotite,hornblende,olivine,[3]plagioclase and bothorthopyroxene andclinopyroxene;[11] alteration has led to the formation ofclays. The volcanic rocks are subdivided into two units, an andesitic-dacitic one that forms the bulk of the volcano dacitic lava dome.[8]
Tacora was active during thePleistocene andHolocene epochs[4] less than 700,000 years ago,[30] with one rock sample dated bypotassium-argon dating giving an age of 490,000 years before present,[11] an age often given to the entire volcano,[16] as well as another of 50,000 years before present on the upper western flank.[12] Other dating efforts have yielded ages of 340,000 ± 60,000 and 363,000 ± 7,000 years ago.[8] The crater and lava flows on the southern flank are probably the most recent manifestations of volcanic activity.[3] Tacora is a possible source of theAD 400-720 Khonkho tephra.[42]
The volcano supposedly "collapsed" in the1877 Iquique earthquake, according to secondhand information in a 1903 report on earthquakes in Chile.[43] Single reports of activity in 1830, 1930, 1937, 1939 and 1950 exist,[12][44] but the volcano is considered to have no historic eruptions, with fumaroles[7] andseismicity the only ongoing activity.[12] Renewed activity is likely to mostly affect the southern, eastern and western slopes of the volcano. In particular the town of Tacora would be threatened, whilepyroclastic fallout could impact more distant towns such asVisviri.[44]
Sulfur is found between Tacora and Chupiquiña, and it has been quarried on the northwestern flank.[3] Sulfur deposits on Tacora are among the largest in Chile, with thick layers of sulfur covering surfaces of 0.2–0.3 square kilometres (0.077–0.116 sq mi) in the crater and on the northern and eastern slopes.[45] Fumarolic activity is to this day producing new sulfur deposits,[24] and some sulfur deposits may have been originally emplaced as liquid sulfur.[46]
Such sulfur deposits are relatively common on volcanoes of northern Chile, with less common occurrence in the other volcanically active parts of the Chilean Andes;[47] nearly all higher volcanoes in northern Chile are reported to host the mineral.[48] The sulfur develops chiefly fromhydrogen sulfide in steam, which precipitates the mineral in rock cavities. Sulfur deposits are typically accompanied by discoloured rocks, since the formation of the sulfur is usually associated withhydrothermal alteration of rock formations. These colours can be spotted from large distances. Aside from sulfur, such deposits commonly containantimony,arsenic,selenium andtellurium;[49]acid mine drainage occurs on the volcano and has resulted in pollution of the Azufre River within theLluta River watershed.[50]
The earliest records of the sulfur bodies on Tacora date back to 1637.[51] Sulfur mining in Chile commenced in the late 19th century, driven by Peruvian, English and Chilean prospectors[52] and because the world demand of sulfur by the chemical industry and for other uses increased substantially at that time.[53] During the early 20th century, sulfur mining was widespread in northern Chile and of high global importance,[54] a number of highly pure deposits of sulfur can be found in northern Chile from the Peruvian border south to thePuna de Atacama region.[55]
A. Barrón, Filomeno Cerda, Luis Koch and Rosa Landaeta owned sulfur deposits on Tacora in 1897, and sulfur processing plants were installed in 1888 and 1900 close to Tacora. Several companies mined in the region, which later were sometimes taken over by foreign corporations.[56] A number of mines were active on Tacora volcano,[51] with much of the mining infrastructure being present on the upper northwestern slopes of the mountain;[57] this infrastructure includescableways, offices, workers' camps and treatment plants both on the mountain and on its foot.[53] The deposits were named Aguas Calientes, Ancara, Chislluma, Santa Elena and Villa Industrial,[58] and the total sulfurore deposits of Tacora in 1952 were estimated to be 2,000,000 tonnes (2,000,000 long tons; 2,200,000 short tons) at a minimum;[59] in 1922 Tacora was considered the most important sulfur deposit of the Andes.[60]
Transport of sulfur occurred through a dedicatedrailroad down toVilla Industrial on theArica-La Paz railway,[61] which served the further transport of the sulfur[51] toArica, from where it was shipped to all of South America;[62] only after the opening of this railway in 1913 was it possible to use the Tacora deposits to the fullest extent.[53] It is worth noting that the1929 border treaty between Peru and Chile had explicitly placed Tacora's sulfur deposits entirely within Chilean territory.[62]
The workforce of the Tacora mines was largely indigenous in origin, seeing as only indigenous people were used to the extreme climate conditions on the upper slopes of Tacora. The mining operations also played an important political-cultural role, as they exemplified the imposition of a new, modern culture onto the region.[53]
The religious worship of mountains is widespread in the Central Andes. In local belief, Tacora andSajama were two mountains in competition for two women (theNevados de Payachata). Depending on the specific myth either the two women drove Tacora off and removed the top of the mountain, or Sajama did and injured Tacora; Tacora subsequently fled, shedding blood and a piece of its heart.[63]
TheAstragalus speciesAstragalus tacorensis is named after the volcano, which is itstype locality.[64] The flowering plantPycnophyllum macropetalum likewise has its type locality at Tacora.[65]
{{cite web}}: CS1 maint: others (link){{cite book}}: CS1 maint: publisher location (link)tacora.
{{cite book}}:|work= ignored (help)