El Tatio

El Tatio is a geyser field located in the Andes Mountains of northern Chile at 4,320 metres (14,170 ft) above mean sea level. Various etymologies have been proposed for the name "El Tatio", which might mean "oven" or "grandfather". It is the third-largest geyser field in the world and the largest in the Southern Hemisphere.

El Tatio geyser field

El Tatio lies at the western foot of a series of stratovolcanoes, which run along the border between Chile and Bolivia. This series of volcanoes is part of the Central Volcanic Zone, one of several volcanic belts in the Andes, and there are no recorded historical eruptions at the Tatio volcanoes. El Tatio is also part of the Altiplano–Puna volcanic complex (APVC), a system of large calderas and associated ignimbrites, which have been the sources of supereruptions. Some of these calderas may be the source of heat for the El Tatio geothermal system.

El Tatio is a geothermal field with many geysers, hot springs, and associated sinter deposits. These hot springs eventually form the Rio Salado, a major tributary of the Rio Loa, and a major source of arsenic pollution in the river. The vents are sites of populations of extremophile microorganisms and have been studied as analogs for the early Earth and possible past life on Mars.

The field is a major tourism destination in northern Chile. It was prospected over the last century for the potential of geothermal power production, but development efforts were discontinued after a major incident in 2009 in which drilling well blew out, creating a steam column. The blowout caused a political controversy about geothermal power development in Chile.

Name and research history

The term "tatio" is Kunza and means "to appear", "oven",[1] but it has also been translated as "grandfather"[2] or "burnt". The geyser field is also known as the Copacoya geysers.[3]

The earliest mentions of geysers in the region are from the late 19th century,[4] and they were already well known by 1952.[5] The first geothermal prospecting of the field occurred in the 1920s[6] and the field was mentioned in academic literature in 1943,[7] but more systematic research took place in 1967–1982;[8] most research on this geothermal field was done in the context of geothermal prospecting.[9]

Geomorphology and geography

El Tatio lies in the Antofagasta Province of northern Chile close to the border between Chile and Bolivia.[10][lower-alpha 1] The field is located 89 kilometres (55 mi)[12]-80 kilometres (50 mi) north of the town San Pedro de Atacama and 100 kilometres (62 mi) east of the town of Calama;[13] Chile Route B-245 connects El Tatio to San Pedro de Atacama.[14] Towns close to El Tatio are Toconce to the north, Caspana to the west, Machuca to the south[15] and a workers' camp for a sulfur mine at Volcan Tatio, which was reported to exist in 1959.[16] The old Inca trail from San Pedro de Atacama to Siloli crossed the geyser field;[3] the Inca also operated a mountain sanctuary on Volcan Tatio.[17] There are several unpaved roads and all parts of the field are easily accessible.[18]

El Tatio is part of the Central Volcanic Zone, a segment of the Andes between 14° and 28° southern latitude where the Andes are volcanically active. This volcanism manifests itself with about 10 silicic caldera complexes of the Altiplano–Puna volcanic complex and more than 50 recently active volcanoes; Lascar in 1993 erupted and produced a tall eruption column.[19]

Andesitic stratovolcanoes reaching elevations of about 5,000 metres (16,000 ft) are found at El Tatio east of the field,[19] while the Sierra de Tucle lies to the southwest of it.[20] From north to south the andesitic stratovolcanoes include the 5,651-metre (18,540 ft)[21][7][22] or 5,696 metres (18,688 ft) high Cerro Deslinde which is the highest in the area,[23] the 5,560-metre (18,240 ft) high Cerro El Volcan, the 5,280–5,570-metre (17,320–18,270 ft) high Cordillera del Tatio and the 5,314-metre (17,434 ft) high Volcan Tatio, and they collectively form the El Tatio volcanic group.[21][7][22][lower-alpha 2]

Mountains southwest of El Tatio include the 4,570–4,690-metre (14,990–15,390 ft) Alto Ojo del Cablor, while 4,812-metre (15,787 ft) high Cerro Copacoya is situated northwest of the geothermal field.[24] Dacitic volcanism, older than the easterly stratovolcanoes, has occurred west of El Tatio;[7] this volcanism was known as the "liparitic formation" and it covers large areas in the region.[lower-alpha 3][26]

Firn and snow fields were reported in the middle 20th century on the El Tatio volcanic group, at elevations of 4,900–5,200 metres (16,100–17,100 ft).[27] The region is too dry to support glaciers today,[28] but in the past higher moisture allowed their formation on mountains of this part of the Andes;[29][30] glacially eroded mountains and moraines testify to their existence[31] in the form of large valley glaciers.[23] A large moraine complex, including both terminal structures and well-developed lateral moraines, can be found north of the geyser field[32] and reflects the existence of a 10 kilometres (6.2 mi) long glacier, the longest valley glacier in the region.[33] Two more moraine systems extend westward both northeast and southeast of El Tatio, and the terrain surrounding the geyser field is covered by sands that are interpreted as glacial outwash sands.[34] Surface exposure dating indicates that some moraines were emplaced at or before the Last Glacial Maximum and others in a time period 35,000 to 40,000 years before present.[lower-alpha 4][36] Smaller moraines at higher altitude may date to the Antarctic Cold Reversal or the Younger Dryas climate periods;[37] moraines related to the Lake Tauca stage are either absent or restricted to high elevation sites.[38]

Drainage in the area is generally from east to west down the Western Cordillera,[39] often in form of steeply incised valleys.[16] The Rio Salado drains most of the hot spring water[39][40] and has its headwaters in the field[9] where it is joined by the Rio Tucle.[39][40] Temperature measurements of the water flowing to the Rio Salado have yielded values of 17–32 °C (63–90 °F),[27] while the discharge of the Rio Salado amounts to 0.25–0.5 cubic metres per second (8.8–17.7 cu ft/s).[41] The Rio Salado eventually joins the Rio Loa, a major source of freshwater for the region;[9] thus, El Tatio plays an important role in the regional water supply.[42]

Geothermal field

El Tatio is well known as a geothermal field in Chile,[10] and is the largest geyser field in the southern hemisphere with about 8% of all geysers in the world and is (together with Sol de Mañana, which is just east of El Tatio in Bolivia[43]) the highest geyser field in the world.[44][13] Only Yellowstone in the United States and Dolina Geizerov in Russia are larger[44] and their geysers are taller than these at El Tatio.[45]

The Andes rise behind El Tatio

The geothermal field covers an area of 30 square kilometres (12 sq mi) at elevations of 4,200–4,600 metres (13,800–15,100 ft), and is characterized by fumaroles, hot springs, steam vents known as soffioni and steaming soil. Stronger geothermal activity is located within three discrete areas covering a total of 10 square kilometres (3.9 sq mi) surface, and includes boiling water fountains, hot springs, geysers, mudpots, mud volcanoes and sinter terraces;[46][13] further, chimneys of extinct geysers have been noted.[47] About 110 documented geothermal manifestations occur at El Tatio, and a total number of 400 has been estimated.[48] One of these three areas lies within a valley, the second on a flat surface and the third along the banks of the Rio Salado.[4] The first area offers a notable contrast between the snow-covered Andes, the coloured hills that surround the field and the white deposits left by the geothermal activity. Most geysers of El Tatio are found here and are particularly noticeable in cold weather. A similar landscape exists at the third (lower) area, with the presence of the Rio Salado river adding an additional element to the landscape.[49][50] The second area is located between a creek and a hill and includes an artificial 15-by-30-metre (49 ft × 98 ft) pool for tourists.[51]

The field once numbered 67 geysers and more than three hundred hot springs. Many vents are linked to fractures that run northwest-southeast or southwest-northeast across the field.[22] Some geyser fountains reached heights greater than 10 metres (33 ft);[52] usually, however, they do not exceed 1 metre (3 ft 3 in)[44] and their activity sometimes varies over time.[53] A few geysers have received names, such as Boiling Geyser, El Cobreloa, El Cobresal, El Jefe, Terrace Geyser, Tower Geyser and Vega Rinconada.[54][55][56] Minor eruptions of the geysers occur approximately every dozen minutes and major eruptions every few hours on average, and major eruptions appear to be preconditioned by smaller ones.[57] An additional geothermal system lies southeast of and at elevations above El Tatio and is characterized by steam-heated ponds fed by precipitation water,[9] and solfataric activity has been reported on the stratovolcanoes farther east.[26]

The sinter landscape formed at El Tatio

Deposition of sinter from the waters of the geothermal field has given rise to spectacular landforms, including, but not limited to mounds, terraced pools, geyser cones and the dams that form their rims.[22][46] Small scale features include cones, crusts, mollusc-shaped formations, waterfall-like surfaces[58] and very small terraces.[59] These sinter deposits cover an area of about 30 square kilometres (12 sq mi) and include both active and inactive deposits,[60] both of which were emplaced on glacial sediments.[61] High contents of silica give the waters a blueish colour, organic compounds such as carotenoids conversely often colour the sinter with orange-brown,[62] and greenish hues are owing to iron-oxidizing bacteria.[63]

  • Hot springs form pools with water temperatures of 60–80 °C (140–176 °F), which are often gently moving and surging and in the case of the warmer springs actively bubbling. These pools often contain ball-like rocks called oncoids and are surrounded by sinter rims, which have spicule-like textures.[64] These sinter rims often form dam-like structures around deeper vents which are filled with water.[65] Spherical grains develop in the hot springs as a consequence of hydrodynamic processes, and include biogenic material; during the growth of the sinter they often end up embedded in the material.[66]
  • Flowing water that drains from the springs deposits sinter, which can form fairly thick deposits and large aprons when sheet flow occurs, known as "discharge deposits"; sometimes terraces are developed instead. As in springs, oncoids and spicules are observed in channels. Much of the water evaporates and its temperature drops from 30–35 °C (86–95 °F) to less than 20 °C (68 °F) away from the springs;[67] the low air temperatures cause it to freeze occasionally, resulting in frost weathering.[68]
  • Geysers and also water fountains discharge from up to 3-metre (9.8 ft) high cones[69][65] with gently sloping surfaces, which sometimes support splash mounds[70] and are constructed by geyserite.[71] Other geysers and fountains instead discharge from within rim-bounded pools,[69] and some geysers are located on the bed of the Rio Salado river.[4] The activity of geysers is not stable over time, changes in water supply or in the properties of the conduit that supplies them can cause changes in their eruptive activity. Such changes can be triggered by rainfall events or earthquakes and at El Tatio geyser behaviour changes have been linked to the 2014 Iquique earthquake and a 2013 precipitation event.[72] The water of geysers is 80–85 °C (176–185 °F) warm.[70]
  • Mud pools are often bubbling, with the hot mud fountaining.[27] Simmering pools of water have been recorded at El Tatio as well.[3]
  • A vent surrounded by yellow rocks
  • Geyser cone
  • Geyser cone
  • Geyser cone

Geology

Subduction of the Nazca Plate beneath the South American Plate is responsible for the formation of the Andes. Volcanism does not occur along the entire length of the Andes; there are three volcanic zones called the Northern Volcanic Zone, the Central Volcanic Zone and the Southern Volcanic Zone, all separated by areas with no recent volcanism.[19][73]

El Tatio and a number of other geothermal fields such as Sol de Mañana are part of the Altiplano–Puna volcanic complex. The region was dominated by andesitic volcanism producing lava flows until the late Miocene, then large scale ignimbrite activity took place between 10 and 1 million years ago. This ignimbrite volcanism is part of the APVC proper and produced about 10,000 cubic kilometres (2,400 cu mi) of ignimbrites, covering a surface area of 50,000 square kilometres (19,000 sq mi). The APVC activity continued into the Holocene with the emission of voluminous lava domes and lava flows,[18][19] and Tatio was one of the last volcanic centres in the APVC to erupt;[74] the present-day uplift of the Uturunku volcano in Bolivia may signal ongoing activity of the APVC.[75] The APVC is underpinned by a large magma chamber with the shape of a sill, the Altiplano-Puna Magma Body; a number of volcanoes and geothermal system including El Tatio are geographically associated with the Altiplano-Puna Magma Body.[76]

The Laguna Colorada caldera lies east of El Tatio.[19] The terrain at El Tatio is formed by Jurassic–Cretaceous sediments of marine and volcanic origin, Tertiary–Holocene volcanic formations that were emplaced in various episodes, and recent sediments formed by glaciers, alluvium, colluvium and material formed by the geothermal field, such as sinter.[77][22] Volcanic formations fill the Tatio graben, including the Miocene Rio Salado ignimbrite and related volcanics which reach thicknesses of 1,900 metres (6,200 ft) in some places, the Sifon ignimbrite, the Pliocene Puripicar ignimbrite and the Pleistocene Tatio ignimbrite;[78][79] the Puripicar ignimbrite crops out farther west.[80] Active volcanoes in the area include Putana and Tocorpuri.[81]

Hydrothermal alteration of country rock has occurred at El Tatio, it has yielded large deposits of alteration minerals such as illite, nobleite, smectite, teruggite and ulexite.[78] Likewise, the summit parts of several volcanoes of the El Tatio volcanic group have been bleached and discoloured by hydrothermal activity.[82]

Hydrology

Most of the water that is discharged by the hot springs appears to be precipitation, which enters the ground east and southeast of El Tatio. The source of heat of the whole complex appears to be the Laguna Colorada caldera,[83][22][84] the El Tatio volcanic group[41][46] or the Cerro Guacha and Pastos Grandes calderas.[85][15] The movement of the water in the ground is controlled by the permeability of the volcanic material and the Serrania de Tucle–Loma Lucero tectonic block west of El Tatio that acts as an obstacle.[22][84][86] As it moves through the ground, it acquires heat and minerals[20] and loses steam through evaporation. Unlike geothermal fields in wetter parts of the world, given the dry climate of the area, local precipitation has little influence on the hot springs hydrology at El Tatio.[87] Neither magmatic water nor water from precipitation are mixed into this water.[88] The time the water takes to traverse the whole path from precipitation to the springs is about 15 years[10] and three quarters of the heat are transported by steam.[89]

The water travels through a number of aquifers that correspond to permeable rock formations, such as the Salado and Puripicar ignimbrites,[90][88] as well as through faults and fractures in the rock.[15] It steeply ascends under El Tatio[91] and appears to be confined between northeast-trending fault systems.[92] Three separate geothermal reservoirs have been identified, named "A", "B" and "C", which underlie the Cerros del Tatio, extend to the La Torta volcano and are connected, and partly formed in cavities formed, by faults.[93] The Puripicar ignimbrite appears to be the main hydrothermal reservoir, with temperatures reaching 253 °C (487 °F).[83] The total heat output of El Tatio is about 120–170 megawatts (160,000–230,000 hp).[94] The hydrothermal system beneath El Tatio appears to extend to the neighbouring La Torta system.[95]

Depending on the season, the hot springs yield 0.25–0.5 cubic metres per second (8.8–17.7 cu ft/s) of water at temperatures reaching the local boiling point. The water is rich in minerals,[46][84] especially sodium chloride[96] and silica.[61] Other compounds and elements in ascending tendency are antimony, rubidium, strontium, bromine, magnesium, caesium, lithium, arsenic, sulfate, boron, potassium and calcium.[46][84][96]

Some of these minerals are toxic,[62] especially arsenic which pollutes a number of waters in the region.[9] Arsenic concentrations in waters at El Tatio can reach 40 milligrams per litre (2.3×10−5 oz/cu in)[97]-50 milligrams per litre (2.9×10−5 oz/cu in) – among the highest concentrations found in hot springs of the whole world -[98] and 11 grams per kilogram (0.18 oz/lb) in sediments.[99] Producing about 500 tonnes per year (16 long ton/Ms),[100] El Tatio is a principal source of arsenic in the Rio Loa system, and arsenic pollution in the region has been linked to health issues in the population.[101]

Composition of these hot springs is not uniform in El Tatio, with chloride content decreasing from the northern springs over the southwestern ones to the eastern springs, where sulfate is more frequent.[20] This sulfate enrichment appears to be driven by the steam-driven evaporation of the hot spring water,[102] with the sulfate forming when hydrogen sulfide is oxidized by atmospheric oxygen.[103] The decreasing chloride content on the other hand appears to be due to drainage coming from the east diluting the southern and western and especially eastern spring systems.[104]

Fumaroles

Steam vents are particularly noticeable in the morning hours when the steam columns emanating from them are particularly visible,[12][47] and temperatures of 48.3–91.6 °C (118.9–196.9 °F) have been found.[105] Carbon dioxide is the most important fumarole gas, followed by hydrogen sulfide.[105][84][52] The amount of water relative to these two gases is variable, probably due to condensation of water in the ground.[106]

Additional components include argon, helium, hydrogen, methane, neon, nitrogen and oxygen. Characteristically for fumarole gases on convergent plate boundaries, much of this nitrogen is non-atmospheric, although atmospheric air is also involved in generating the chemistry of the El Tatio fumarole gases.[107]

Composition of spring deposits

Opal is the most important component of sinter associated with hot springs; halite, sylvite and realgar are less common.[67] This dominance of opal is because usually conditions favour its precipitation from water but not of other minerals,[108] and it occurs both in subaqueous environments and on surfaces that are only occasionally wetted. During the precipitation, the opal forms tiny spheres which can aggregate as well as glassy deposits.[109]

Halite and other evaporites are more commonly encountered on the sinter surfaces outside of the hot springs,[110] and while opal dominates in these environments as well sassolite and teruggite are found in addition to the aforementioned four minerals in the discharge deposits. Volcanic rock fragments such as plagioclase and quartz are found within cavities of the sinter.[70]

Cahnite has also been identified in sinter deposits.[111] Finally, antimony, arsenic and calcium form sulfidic deposits in some springs.[112] Microorganisms and material like pollen is found integrated within the sinter deposits.[69] The rate at which sinter is deposited has been estimated at 1.3–3.4 kilograms per square metre per year (0.27–0.70 pdr/sq ft/a).[46]

Climate and biology

The climate is dry with most precipitation falling between December and March,[84] a precipitation pattern mediated by the South American monsoon[113] and by the South Pacific High which is responsible for the dry climate.[114] The whole Central Andes were wetter in the past, resulting in the formation of lakes such as Lake Tauca in the Altiplano.[29] This, and a colder climate, resulted in the development of glaciers at El Tatio, which have left moraines.[115]

The region is additionally rather windy[116] with mean windspeeds of 3.7–7.5 metres per second (12–25 ft/s),[61] which influence the hot springs by enhancing evaporation.[116] The evaporation rates per month reach 131.9 millimetres (5.19 in)[61] and they facilitate the deposition of sinters.[117]

Apart from precipitation, the area is characterized by extreme temperature variations between day and night[84] which can reach 40 °C (72 °F).[60] The Chilean Dirección General del Agua operates a weather station at El Tatio; according to data from this station air temperatures average 3.6 °C (38.5 °F) and precipitation 250 millimetres per year (9.8 in/year).[118][119] El Tatio further features high ultraviolet (UV) insolation.[55]

Landscape of the El Tatio region

The dry grassland vegetation of the region is classified as Central Andean dry puna[84] and lies above the treeline.[118] Tussock grasses like Anatherostipa, Festuca and Stipa occur at 3,900–4,400 metres (12,800–14,400 ft) elevation, while rosette and cushion plants reach elevations of 4,800 metres (15,700 ft); these include Azorella, Chaetanthera, Mulinum, Senecio, Lenzia, Pycnophyllum and Valeriana. Riparian vegetation occurs along the Rio Salado.[120] Among the animals in the region are chinchillas and viscachas and llamas, mainly the vicuña.[2]

Spring biology

The geothermal field El Tatio is populated by various plants, microbes and animals.[62] The vents are an extreme environment, given the presence of arsenic, the large amount of UV radiation that El Tatio receives[121] and its high elevation.[53]

Hot springs have characteristic microbial communities associated with them that leave characteristic fossil traces in the spring deposits; environmental conditions on the early Earth resembled these of hot springs[46] with potentially high UV radiation exposure, as the ozone layer did not yet exist[122] and life probably developed within such conditions.[123] In addition, microbial metabolism of arsenic influences its toxicity and the effects of arsenic pollution.[124]

Microorganisms

Biofilms and microbial mats are omnipresent at El Tatio,[125] including Calothrix,[69][64] Leptolyngbya,[126] Lyngbya and Phormidium[lower-alpha 5] cyanobacteria, which form mats within the hot springs covering the solid surfaces, including oncoids and the sinter.[69][64] In other places, the aforementioned three genera form stromatolithic structures.[127] Chroococcidiopsis is another cyanobacterium that can be found in hot waters of El Tatio,[128] and non-cyanobacteria bacteria have also been found in the mats and sinter.[129]

There is a thermal gradation of microorganisms, with the hottest waters supporting Chloroflexus green bacteria and hyperthermophiles, cyanobacteria at less than 70–73 °C (158–163 °F) water temperature and diatoms at even lower temperatures.[130] Microbial mats have been found at other hot springs in the world such as Yellowstone and Steamboat Springs, both in the United States, and New Zealand, but they are thinner at El Tatio.[131]

These mats often have their organic material replaced with opal and thus end up forming much of the sinter, which has thus characteristic biogenix textures, such as filaments and laminae.[64] Such biogenic textures have been observed on sinter deposits around the world and are usually microbial in origin,[62] at El Tatio they sometimes feature still living bacteria.[132] In the case of El Tatio, these biogenic textures are particularly well preserved in the sinter deposited by water flowing away from springs.[110] Chloroflexus is a thermophilic filamentous green bacterium found in hot waters at Yellowstone; filamentous structures within geyser cones at El Tatio may have been formed by this bacterium.[71] In splash cones Synechococcus-like microbes are instead responsible for the structures, which resemble those of hot springs.[133]

The presence of microorganisms in sinter has been implicated in their tolerance to UV radiation, as sinter absorbs much of this incoming harmful radiation.[134] Some microstructures found on the Home Plate landform on Mars are similar to these biogenic structures at El Tatio, but do not necessarily imply that the microstructures on Mars are biogenic.[135]

Diatoms are also found in El Tatio waters, including Synedra species, which are often found attached to filamentous substrates,[66] and algae are found in the waters.[2] Among bacteria identified in the somewhat colder flowing waters are bacteroidetes and proteobacteria, with Thermus species in the hot waters.[136] Various archaeans have been cultured from El Tatio waters, with hot springs producing crenarchaea, desulfurococcales and methanobacteriales.[137] One species, Methanogenium tatii, has been discovered at El Tatio, and is a methanogen recovered from a warm pool. The species name is derived from the geothermal field[138] and other methanogens may be active in El Tatio.[139]

Macroorganisms

In the upper geyser basin, vegetation has been observed to grow within thermal areas, like a thermal marsh.[140] Animal species found at El Tatio include the snail Heleobia[141] and frog Rhinella spinulosa.[142] The larvae of this frog at El Tatio live in water with approximately constant temperatures of 25 °C (77 °F) and show atypical development patterns than frogs of the same species that developed in places with more variable water temperatures.[143]

Geological history

During the Pliocene–Quaternary the Western Cordillera was subject to extensional tectonics. A related fault system was active; it is linked to Sol de Mañana in Bolivia[144] and controls the position of several vents in El Tatio.[41] The intersection between northwest-southeast trending and northnorthwest-southsoutheast-trending lineaments at El Tatio has been correlated with the occurrence of geothermal activity.[145] The tectonics of the El Tatio area were originally interpreted as reflecting the existence of a graben before a compressive tectonic regime was identified.[91]

A series of ignimbrites was emplaced.[146] The first was the 10.5–9.3 million years old[lower-alpha 6] Rio Salado ignimbrite, which forms a 1,800-metre (5,900 ft) thick layer; this might imply that the source of this ignimbrite was close to El Tatio. The Rio Salado ignimbrite elsewhere crops out as two flow units, with varying colours, and close to El Tatio it is crystalline and densely welded.[147] It was followed by the 8.3 million years old voluminous Sifon ignimbrite, which reaches a thickness of about 300 metres (980 ft) in the area.[146] The Pliocene Puripicar ignimbrite reaches a similar thickness,[149] and it was later downwarped by faulting.[150]

This strong ignimbrite volcanism is associated with activity of the Altiplano–Puna volcanic complex, which has produced dacite dominated large volume ignimbrites and sizable calderas, starting from the middle Miocene. Among these, Cerro Guacha, La Pacana, Pastos Grandes and Vilama produced supereruptions.[151]

The Tatio ignimbrite was emplaced less than one million years ago, while the Tucle volcanics are dated to 800,000 ± 100,000 years ago.[152] The ignimbrite reaches a volume of 40 cubic kilometres (9.6 cu mi) and crops out over a surface area of 830 square kilometres (320 sq mi).[153] The Tatio ignimbrite contains rhyolitic pumice and crystals, while the Tucle volcanics are andesitic and include both lava and tuffs.[149] The El Tatio ignimbrite ponded in the El Tatio area and may have originated at the Tocorpuri rhyolite dome, which is less than one million years old,[150] in a vent now buried beneath the El Tatio volcanic group,[154] or at the Laguna Colorada caldera.[155]

The El Tatio volcanic group has likewise been dated to be less than one million years old,[156] and its lavas overlie the older formations.[157] Volcan Tatio erupted mafic[lower-alpha 7] lavas probably during the Holocene;[16] later this volcano was reinterpreted to be of Pleistocene age.[21] Petrological data suggest that over time the erupted lavas of the El Tatio volcanic group have become more mafic, with older products being andesitic and later ones basaltic-andesitic.[82]

There is no recorded historical volcanism in the El Tatio area[46] and volcanism has not directly affected it since about 27,000 years.[159] Based on the rates of sinter precipitation and the thickness of the sinter deposits, it has been estimated that the sinters at El Tatio started to form between 4,000 and 1,500 years ago; these age estimates were not based on direct dating of the deposits, however,[116] and older sinter deposits extend past the present-day geothermal field.[160] Later, radiocarbon dating of the sinter deposits found that their deposition began after the end of the last ice age,[161] an observation endorsed by the presence of glacial deposits beneath the sinter[46] and radiocarbon dating evidence that sinter deposition began after glaciers retreated.[162] Research published in 2020 suggests that the geothermal activity commenced in the southern part of the field about 27,000 - 20,000 years ago and spread northwards, reaching the western part of the field last less than 4,900 years ago.[163] Secular variations in the deposition rate have been found, with an increase noted in the last 2,000 years.[161]

Human exploitation
Technical equipment at El Tatio

Geothermal power is the energy that comes from the internal heat of the Earth, and where the heat flow from the interior of the globe is sufficiently high it can be used both for heating purposes and for the generation of electrical power. As of 2010, about 10.9 gigawatt geothermal energy are produced on Earth, not all of this production is linked to active volcanism.[164] In the case of Chile however various legal and economic hurdles have so far prevented substantial development of geothermal energy in the country.[165][166]

The earliest references to geothermal power at El Tatio go back to the beginning of the 20th century, when a private society "Comunidad de El Tatio" was formed and employed Italian engineers from Larderello, which in 1921 and 1922 probed the field.[167] Technical and economic problems prevented this first effort from further progress.[168] Feasibility studies in northern Chile identified El Tatio as a potential site for geothermal power generation, with large scale prospecting taking place in the 1960s and 1970s. In 1973 and 1974, wells were drilled and it was estimated that if the geothermal resources were fully exploited, about 100–400 megawatts (130,000–540,000 hp) electric power could be produced.[78] Also in 1974 a desalination facility was built at El Tatio and can still be seen there today;[4] a thermal desalination process was developed at El Tatio, which could be used both for creating fresh water and brine that could be reprocessed for valuable minerals.[169] Drilling substantially altered the behaviour of the hot springs; already in November 1995, reports indicated that a number of geysers had disappeared or become hot springs and fumaroles.[52]

El Tatio is remote and this along with economic difficulties eventually led to the abandonment of the efforts at power generation;[78] a bidding process for exploration rights in 1978 to attract private companies to El Tatio was interrupted by government changes[168] and until 2000 geothermal development programs were paralyzed.[89]

More recently in the 2000s several companies expressed interest at restarting geothermal power projects at El Tatio.[78] A dispute over gas supplies for Northern Chile from Argentina in 2005 helped push the project forward,[170] and after an environmental impact review in 2007[171] the Chilean government in 2008 granted a concession to develop geothermal resources in the field, with the expected yield being about 100,[121][172] 60,[173] 50[172] or 40 megawatt.[lower-alpha 8] The first drilling permits were issued for the Quebrada de Zoquete area 4 kilometres (2.5 mi) away from the main field.[174] It progressed until 2009, when an incident at the site along with environmental issues caused it to stall again.[175]

Controversy
Steam venting created by the geothermal well blowout

On 8 September 2009, a well that was being bored in El Tatio blew out, generating a 60-metre (200 ft) high steam fountain[176] that was not plugged until 4 October.[177] The operator of the geothermal project restricted access to the blow-out vent and stated through the technical manager of the El Tatio geothermal project that the blowout was neither a threat to the springs nor to tourists visiting El Tatio, and the Empresa Nacional de Geotermia company that operates it denied any responsibility for the incident.[178]

The project had earlier been opposed by the local Atacameno population, owing to concerns about environmental damage.[170] Before the incident, an issue of the English-language newspaper The Economist had called attention to the adverse consequences of geothermal power extraction;[179] the incident triggered a major controversy about geothermal power, with ramifications beyond Chile.[121] The controversy gained international attention[180] and involved public demonstrations against the project and the march of two women to the capital Santiago to defend the geothermal field.[181] The environmental authorities of Antofagasta subsequently suspended the El Tatio geothermal project, and the Geotérmica del Norte[lower-alpha 9] company responsible for the project received strong criticism and was targeted by legal action. Both the Ministers of Mining and Energy cautioned against stigmatizing geothermal energy, however,[182] and some local authorities disagreed with the rejection.[181] The director of the National Geology and Mining Service (SERNAGEOMIN) stated that the company had no plans to handle such a situation.[177] The Geotérmica del Norte company was fined 100 UTM[lower-alpha 10] for violating mitigation plans, a fine upheld in 2011 by the Court of Appeals in Santiago.[183]

Industry-community disputes have occurred before in northern Chile, typically tied to conflicts about the use of water,[lower-alpha 11] which was in large part privatized during the Pinochet era; during the Tatio controversy power generation also gained prominence among the disputed issues. An important factor in the Tatio controversy is the role of the tourism industry, which viewed the geothermal project as a threat; this kind of industry-industry conflict was unusual.[185] Geothermal projects in New Zealand and the United States have resulted in the extinction of geysers, and the tourism industry of the region had been opposed to the project for a while.[186] While the incident ultimately did not result in lasting changes to the El Tatio geysers, the widespread media attention did create adverse publicity and social opposition against geothermal energy in Chile.[166]

Tourism

El Tatio is a tourism destination, with substantial numbers of travelers both from Chile and other countries. This tourism is an important economic resource for the region,[187][121] and the site is administered by the local Atacameno population.[170] In 2009, there were more than 400 daily visitors of the geysers, about 90 percent of all tourism of San Pedro de Atacama[186] from where El Tatio can be reached.[14] Aside from viewing the geysers, bathing in the hot water and watching the natural scenery are other activities possible at El Tatio.[188] Environmental impacts such as pollution and vandalism of geothermal landforms has been documented.[2]

Safety warning sign

El Tatio displays some typical hazards of geothermal areas.[189] Exposure to the hot gases and water can result in burn injuries, and both sudden eruptions of geysers and fountains and fragile ground above vents and above boiling water, concealed beneath thin covers of solid ground, increase the risk to unwary travelers.[190] The site lies at high altitude, frequently leading to altitude sickness, and the cold dry climate creates further danger.[191] The Chilean government recommends that tourists take warm clothing, sunscreen and mineral water.[12]

In 2010, the El Tatio area was declared to be a protected area, with a surface area of 200 square kilometres (20,000 ha). It was not clear at that time what the exact status would be, with the regional Secretary of Agriculture proposing that it should become a national park.[192]

See also

Notes
  1. As established by the Treaty of Peace and Friendship of 1904, the border between Bolivia and Chile runs along the drainage divide on the Cordillera del Tatio.[11]
  2. The toponymy of the Cordillera del Tatio varies between maps.[23]
  3. The "Liparitic formation" was later split up in a number of additional geological formations.[25]
  4. Elsewhere in the Central Andes a glacier advance has been inferred about 40,000 years ago, at the same time as the Inca Huasi lake stage in the Altiplano.[35]
  5. Phormidium is not strictly speaking a genus; it is defined by the morphology of the bacterial colonies and their silicified fossils. Phormidium mats are found in other geothermal areas around the world and additionally on wet soil.[64]
  6. Originally it was considered to be 9.56 ± 0.48 million years old,[147] but later it was split into a 10.5 and a 9.3 million years old ignimbrite.[148]
  7. A volcanic rock relatively rich in iron and magnesium, relative to silicon.[158]
  8. According to the manager of the Chilean geothermal company, enough to power 130,000 homes and to save on 240,000 tons of carbon dioxide emission every year.[174]
  9. A daughter firm of Empresa Nacional de Geotermia.[177]
  10. About US$4 million in 2011.[183]
  11. The region is arid and economic growth driven by increased mining has increased the consumption of the scarce water resources in the region, driving conflict between various entities.[184]

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