| Sairecabur | |
|---|---|
 Sairecabur and Saciel | |
| Highest point | |
| Elevation | 5,971 m (19,590 ft)[1] |
| Prominence | 1,300[2] m (4,300 ft) |
| Parent peak | Acamarachi |
| Coordinates | 22°43′8″S67°53′26″W / 22.71889°S 67.89056°W /-22.71889; -67.89056[1] |
| Geography | |
 | |
| Location | Bolivia–Chile border |
| Parent range | Andes |
| Geology | |
| Mountain type | Stratovolcano |
| Climbing | |
| First ascent | Pre-Columbian[3] |
Sairecabur (Spanish pronunciation:[sajɾekaˈβuɾ]) is avolcano located on the frontier betweenBolivia andChile. It is part of theAndeanCentral Volcanic Zone. Sairecabur proper is 5,971 m (19,590 ft) high; other mountains in the range are 5,722 m (18,773 ft) highCuriquinca, 5,819 m (19,091 ft) high Escalante and 5,748 m (18,858 ft) high Cerro Colorado, all of which have erupted a number oflava flows. Also in close proximity to Sairecabur lie the volcanic centresLicancabur,Putana andJuriques.
Sairecabur proper is accompanied by a 4.5 km (2.8 mi) widecaldera. Before the formation of this caldera the volcano may have been 7,000 m (23,000 ft) high and thus one of thehighest volcanoes on Earth. After the formation of this caldera lava effusion occurred during thePleistocene andHolocene; there is no reported historical activity, however. Eruption products on Escalante and Sairecabur includeandesite anddacite. The climate is dry, cold and very sunny.
An Inca sanctuary has been found on Sairecabur, andsulfur mines exist in the mountain chain. More recently, theReceiver Lab Telescope was installed on the volcano. It is the highestsubmillimeter telescope in the world at an altitude of 5,525 m (18,127 ft).
West of South America, theNazca Platesubducts beneath theSouth America Plate. This process has formed theAndean Volcanic Belt, which is subdivided into theNorthern Volcanic Zone, the Central Volcanic Zone and theSouthern Volcanic Zone. These belts have different underlyingcrusts and thus have different typical magma compositions. These volcanic zones are separated from each other by zones where there is no volcanism, associated with a shallow dip of theseismic zone of the subducting plate.[4]
Sairecabur is part of the Andean Central Volcanic Zone (CVZ).[5] A number ofstratovolcanoes can be found in the area, many of which were affected byexplosive eruptions that have destroyed parts of their edifices.[6] Effusion of large amounts oflava took place from several cones. Many volcanoes areextinct and only a few have documented activity.[7] The geologistJuan Brüggen in 1950 estimated that there were about 800 volcanoes in northern Chile, about 37 of them east of theSalar de Atacama. Also part of the volcanism are largeignimbrites, which are usually thought to be ofMiocene age.[8] Those in the area of Sairecabur often originated in the neighbourhood to the conical volcanoes.[9] The volcanoes formed over crust with thicknesses reaching 70 km (43 mi), thus the erupted magmas are heavily influenced by the crust.[10] A number of the highest stratovolcanoes in the world are in the CVZ. Historical activity has been low in comparison to the volcanic zones of southern Chile and Colombia/Ecuador. In Chile, much of the area of the CVZ isdesert and thus difficult to research.[11]
Sairecabur is constructed on the twoPliocene-Pleistocene Puripicar and Chaxasformations. Some lavas from Sairecabur have also overrun the Purico formation,[12] which is of Pleistocene age and includes ignimbrites from thePurico Complex.[13] The basement beneath Sairecabur and Licancabur contains a large number offaults.[14]
Sairecabur is located at a distance of 25 kilometres (16 mi) fromSan Pedro de Atacama.[15] The volcano saddles the frontier between Bolivia and Chile, where it lies in theAntofagasta Region.[12]Laguna Verde lake, Licancabur volcano and Portezuelo de Chaxas pass lie south of Sairecabur. East of the Sairecabur range lieMount Nelly andCerro Laguna Verde.[16]
TheTreaty of Peace and Friendship (1904) traced the frontier between Bolivia and Chile along the Sairecabur chain.[17] Disagreements between the topographic maps in the two countries mean that the naming of the mountains is often confusing. Escalante is also known as Apagado.[18]
The volcano is associated with amountain range of the same name.[1] The Sairecabur range forms adrainage divide between the Salar de Atacama on the western side and a number of smallendorheic basins in Bolivia on the eastern side. Licancabur and Juriques farther south andTocorpuri farther north are part of the same divide.[19] Dry valleys on the eastern side of the Sairecabur range ultimately drain into Laguna Verde.[16] TheRio Purifica originates on Sairecabur's slope at an altitude of 3,950 metres (12,960 ft),[20] it later converges with theRio Puritama to form theSan Pedro de Atacama River.[21]
The Sairecabur range is a 22-kilometre (14 mi) long chain ofvolcanoes going from Escalante volcano (south ofPutana Volcano) to Sairecabur proper in the south, including at least ten centres which have been active inpostglacial time. Two additional centres exist northeast of Escalante.[18]
5,971-metre (19,590 ft)[a][b] high Sairecabur is the highest volcano in the range. A 4.5-kilometre (2.8 mi) wide caldera exists south of Sairecabur and formed on an older volcano. Lava flows extend from Sairecabur as far as 2.5 kilometres (1.6 mi) to the northwest, and further young lava flows formed south of this caldera.[18] The 5,819-metre (19,091 ft) high[28] Escalante (22°36′45″S67°53′2″W / 22.61250°S 67.88389°W /-22.61250; -67.88389[28]) has acrater lake.[18] Puritama volcano west of Sairecabur has generated 16 kilometres (9.9 mi) lava flows that extend along tectonic canyons.[29] 5,722-metre (18,773 ft) high Curiquinca (22°35′48″S67°51′30″W / 22.59667°S 67.85833°W /-22.59667; -67.85833) and 5,748-metre (18,858 ft) high Cerro Colorado (22°35′29″S67°55′18″W / 22.59139°S 67.92167°W /-22.59139; -67.92167) are found northwest and northeast, respectively, of the range.[1][28]
The caldera is bounded by cliffs reaching a height of 400 metres (1,300 ft), which are buried by lava flows from Sairecabur on the northern rim; one of these lava flows reaches the caldera bottom.[30] The pre-collapse volcano was about 7,000 metres (23,000 ft) high and would have been one of the highest volcanoes in the world;Ojos del Salado reaches an altitude of 6,885 metres (22,589 ft).[31] Sairecabur proper has three cones.[30] Thick (10 metres (33 ft)) and short lava flows emanated from the northern cone.Glacial erosion has affected Sairecabur andmoraines cover some lava flows south of Sairecabur.[31] The total volume of the Sairecabur proper is about 35 cubic kilometres (8.4 cu mi).[12]
Lava flows with a young appearance extend from each of these ten centres. An older centre has generated a 30 kilometres (19 mi) long lava flow that flowed southwestwards.[18] Some older lava flows from Sairecabur were later buried by lava flows from Licancabur.[14]
Cerro Colorado and Curiquinca are aligned in a west–east pattern. Other volcanoes in the area such asLascar-Aguas Calientes, Licancabur-Juriques andLa Torta-Tocorpuri also form such alignments which seem to be controlled by north–south tension in the crust.[32] Sairecabur is located on faults which are also apparent at Laguna Verde.[33]
Escalante and Sairecabur have erupted dark andesites, and later also dacites.[34]Mafic enclaves are found in the post-caldera lavas.[35] The colour of the rocks is black, brown or gray.[36] Minerals includeamphibole,[12]biotite,bronzite,calcium-containingaugite,clinopyroxene,hornblende,magnetite,orthopyroxene,plagioclase,pyroxene andquartz.[34][36][18] In addition,apatite,ilmenite,iron oxides andzirconia are found.[37] At least one lava erupted after the caldera-forming eruption containsolivine. Lavas erupted before the caldera-forming eruption of Sairecabur contain glass and have amicrolithic texture.[36] Themagmas arecalc-alkaline with medium-highpotassium content.[34][35]
Fumarolically altered rocks are found on the eastern flanks of the chain.[18] Desertpatine covers post-caldera lavas.[36]
Based on crystal composition, the magmas of Sairecabur formed at temperatures of 850–950 °C (1,560–1,740 °F). The process started by partial melting of themantle involvingperidotite and subsequent interaction with the crust andfractional crystallization.[34] Andesites erupted before the caldera formation were produced at temperatures 90 °C (160 °F) higher than dacites erupted after the formation of the caldera.[38]Oxygen, lead andstrontium isotope ratios are typical for magmas in CVZ.[18] ThePb isotope ratios are consistent with these found in the crust,[39] specifically of the so-called "Antofalla" domain of Andean crust,[40] the remnant of aterrane ofGondwana.[41]
The 7 million year-old Chaxas ignimbrite massif has been related to the caldera-forming eruption at Sairecabur. These dacitic ignimbrites spread southwest towards the Salar de Atacama.[31] This high age estimate for the Chaxas ignimbrite however has been questioned, considering that it is inconsistent withstratigraphic relationships of this ignimbrite to older ignimbrite.[42] The lava formations are named Post-Caldera Lavas I and Post-Caldera Lavas II; the first is of Pleistocene and the second of Holocene age.[12] A fresh flow that extends northwest from Sairecabur appears to be the most recent flow.[43]
The formation of the caldera occurred before the Holocene[44] and preceded the formation of the other cones in the range.[34] The edifice this caldera formed during the Pliocene-Quaternary considering the morphology of its deposits.[33] During theice ages, a valley due west of the main Sairecabur summit was occupied by a 8-kilometre (5.0 mi) longglacier that extended down to an elevation of 4,600 metres (15,100 ft); the main Sairecabur summit grew inside of the valley occupied by the glacier, which also left lateral and terminal moraines.[45]
Sairecabur volcano is the youngest volcano in the chain; Escalante is also young but not as young as Sairecabur. There are no reports of contemporaneous activity nor hasfumarolic activity been reported,[18] although fumaroles andhot springs were found at the shores ofLaguna Verde which border on Sairecabur.[46] Future activity at Sairecabur may disturb activity atAtacama Large Millimeter Array,[47] and will most likely involve the production of lava domes and lava flows with local impacts.[44]
The climate at Sairecabur is dry and cloudless,[48] leading to the absence of glaciers and permanent snowcover at Sairecabur[49] although a 1985 map shows a persistent ice/snow cover in the summit area[50] and snowfalls can leave temporary snowcover.[51] Overall theAtacama Altiplano has a desert climate with precipitation below 200 millimetres per year (7.9 in/year), but during the late Pleistocene and early Holocene the climate was wetter.[52]Tritium isotope ratios of present-day snowfall are consistent with the isotope ratios determined for precipitation that arises in the continent, rather than from the Pacific Ocean.[53] Therainshadow effect exercised by the Andes and the stability of theSouth Pacific High are responsible for this dryness.[54]
The dry and cloudless climate together with the low latitude and high altitude gives the region some of the highestinsolations on Earth; at Sairecabur it amounts to 98% of thesolar constant.[48] The coincidence between the southern hemispheresummer solstice on 21 December and theperihelion, the point of lowest Earth-Sun distance, on 3 January contribute to the high insolation.[55]Ultraviolet radiation is also high in the area,[56] with values 15.6–36.4 watts per square metre (0.00194–0.00453 hp/sq ft) reported forultraviolet radiation B and ultraviolet radiation A respectively.[57]
Temperatures at 5,820 metres (19,090 ft) ranged from −8.7 to −16.3 °C (16.3 to 2.7 °F) in 1991–1994.[58] A series of measurements in 1995 indicated that surface temperatures at an altitude of 5,820 metres (19,090 ft) range from −20 to 20 °C (−4 to 68 °F) in winter, and soil temperatures at depths of 5 centimetres (2.0 in) also in winter between almost 10 °C (50 °F) and less than −10 °C (14 °F).[59] There are large differences between daytime and night temperatures.[56] Between 1991 and 1994 the average speed of wind amounted to 5–11 metres per second (16–36 ft/s).[58]
Research on plant diversity in the region west of Sairecabur and Licancabur has shown that about 250 plant species occur there,[60] and on the volcano itselfextremophilicyeast species have been found.[61] In 1955,penitentes, a form of ice, was reported to be widespread at Saciel.[62]
The name of the mountain means "rain mountain" in theKunza language, fromSaire "rain" andcabur orcaur "mountain".[63] Sairecabur and Curiquinca both havemountain sanctuaries made by theInca. Licancabur and Juriques farther south were also sites of such sanctuaries.[64] Sairecabur was considered to be asacred mountain,[65] and andesite found at some archeological sites in the Atacama may come from Sairecabur.[66]
A sulfur mine is active at Saciel, north of Sairecabur,[18] and there were sulfur mines and associated infrastructure like relay stations at Sairecabur.[51] Sulfur mining there, at Cerro Colorado and Putana in the 1950s contributed to the growth of San Pedro de Atacama,[67] where the mined sulfur was transported to.[68] A report in 1955 indicated the presence of about 600,000 tonnes (590,000 long tons; 660,000 short tons) ore containing 55–60% sulfur.[69] A 21-kilometre (13 mi) long miningdirt road with a single lane leads from theEl Tatio highway to Sairecabur.[70]
Sairecabur is since 2003 the site of the 0.8-metre (2 ft 7 in) diameter Receiver Lab Telescope,[71] a telescope which operates in theterahertz range of theelectromagnetic spectrum; ground-based astronomy in this range was long considered to be impossible since the atmosphere absorbs radiation in that frequency range heavily.[72] With an altitude of 5,525 metres (18,127 ft) the telescope is the highest submillimeter telescope in the world.[73]
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