| Sollipulli | |
|---|---|
 Aerial photograph of volcan Sollipulli, looking southeast. The dark red feature on the side of Sollipulli is thecinder cone called Chufquen which formed during the most recent eruption, about 700 years ago. | |
| Highest point | |
| Elevation | 2,282 m (7,487 ft)[1] |
| Listing | List of volcanoes in Chile |
| Coordinates | 38°58′30″S71°31′12″W / 38.97500°S 71.52000°W /-38.97500; -71.52000[1] |
| Geography | |
  Sollipulli Location of Sollipulli in Chile | |
| Location | Southern Chile |
| Parent range | Andes |
| Geology | |
| Mountain type | Caldera |
| Volcanic zone | Southern Volcanic Zone |
| Last eruption | 1240 ± 50 years[1] |
Sollipulli (Spanish pronunciation:[soʝiˈpuʝi];lit. 'reddish mountain' in theMapuche language[2]) is an ice-filledvolcaniccaldera and volcanic complex, which lies southeast of the small town ofMelipeuco in theLa Araucanía Region,Chile. It is part of theSouthern Volcanic Zone of the Andes, one of the four volcanic belts in theAndes chain.
The volcano has evolved in close contact withglacial ice. It differs from manycalderas in that Sollipulli appears to have collapsed in a non-explosive manner. The age of collapse is not yet known, but it is presently filled with ice to thicknesses of 650 m (2,130 ft). The ice drains through twoglaciers in the west and the north of the caldera. Sollipulli has developed on a basement formed byMesozoic andCenozoic geological formations.
Sollipulli was active in thePleistocene andHolocene epochs. A largePlinian eruption occurred 2,960–2,780 yearsbefore present, forming the Alpehué crater and generating a higheruption column andignimbrite deposits. The last activity occurred 710 ± 60 years before present and formed the Chufquénscoria cone on the northern flank. Sollipulli is among the 118 volcanoes which have been active in recent history.
Sollipulli lies in theAraucanía Region,Cautín Province,Melipeuco commune.[3] The Sollipulli volcano is in the western part of the Nevados de Sollipulli mountain range, which is bordered to the north, south and east by river valleys.[4] Thecommunes ofCurarrehue,Cunco,Panguipulli,Pucón andVillarrica are in the area,[5]Melipeuco lies 20 km (12 mi) northwest.[6] The volcano is also part of theKütralkura geopark project.[7]
Sollipulli is part of theSouthern Volcanic Zone of the Andes,[8] one of the four belts of volcanoes which are found in the mountain range. The other three are theNorthern Volcanic Zone, theCentral Volcanic Zone (both north of the Southern Volcanic Zone) and theAustral Volcanic Zone (south of the Southern Volcanic Zone). These volcanic zones are separated by gaps where there is no volcanic activity and thesubduction of thePacific Oceancrust is shallower than in the volcanically active areas. About 60 volcanoes have erupted in historical time in the Andes, and 118 additional volcanic systems show evidence ofHolocene eruptions.[9]
There are 60 volcanoes in the Southern Volcanic Zone; among these areCerro Azul andCerro Hudson, which experienced large eruptions in 1932 and 1991 that resulted in the emission of substantial volumes of ash. The volcanoesLlaima andVillarrica have been regularly active during recent history.[9]
Sollipulli is astratovolcano,[4] which has one 4 km-wide (2.5 mi) caldera on its summit and southwest of it the 1 km-wide (0.62 mi) Alpehué crater.[6] The crater is draped bypyroclastic flow deposits, and its rim reaches a height of 200 m (660 ft).[10] The rims of the caldera rise 150 m (490 ft) above the ice in the caldera;[11] the highest summit of Sollipulli lies on the southern flank of the caldera and reaches an elevation of 2,282 m (7,487 ft) above sea level.[4] On the southern and eastern side the caldera is bordered by severallava domes.[1] The caldera most likely was not formed by a large explosive eruption, considering that no deposits from such an eruption have been found.[12] An older 5 km × 4 km-wide (3.1 mi × 2.5 mi) caldera underlies the summit caldera.[13]
The volcano is formed bylava flows,lava domes,scoria,pillow lavas as well aspumice falls,pyroclastics and other material.[14] The edifice has a volume of about 85 km3 (20 cu mi) and covers a surface area of about 250 km2 (97 sq mi). Radial valleys extend away from the top.[4] A number of particular landforms on Sollipulli formed under the influence of glacial ice, such as the caldera structure.[15]
The Nevados de Sollipulli mountain chain west of the Sollipulli caldera are a chain of volcanoes which is heavily eroded. They are formed bybreccia andlava flows; glacial action has leftcirques. Closer to the caldera they are better preserved, with individual flows issuing fromfissure vents.[16] This chain is one of several east–northeast striking volcano alignments in the Southern Volcanic Zone, the regional tectonics favour magma ascent along such alignments.[17]
The flanks of the volcano are covered bylava flows, which gives them irregular contours. Glaciers and streams have cut valleys into the slopes and smoothed the lava flows.[18] Twoscoria cones are situated on the northern flank, Chufquén and Redondo, each associated withlava flows;[6] about a dozen such craters dot the flanks of the volcano.[19]
Both the main caldera and the Alpehué crater contain glaciers,[6] which in the caldera reached a thickness of 650 m (2,130 ft) in 1992[20] and fills it;[6] the total volume was estimated at 6 km3 (1.4 cu mi) in 1992.[21] These glaciers feature typical ice structures such ascrevasses and there may be asubglacial lake in the caldera.[14] Three lakes are found in the caldera at its margins, the easterly Sharkfin lake, the southeasterly Dome lake and the southwesterly Alpehué lake. These glaciers drain to the north and northwest; the latter glacier flows from the caldera through the Alpehué crater into the valley of the same name,[11] which is drained by theRio Alpehué into theRio Allipén river.[6] Other than the caldera and crater glaciers, the only snow cover on Sollipulli is seasonal.[8] Glaciers have been present on the volcano before theLast Glacial Maximum[22] and have leftglacial valleys on its slopes,[23]glacial striations and evidence ofsubglacial eruptions such ashyaloclastite deposits.[24]
The glacier within the caldera of Sollipulli is shrinking;[25] its surface area decreased between 1961 and 2011 and the Alpehuén outlet glacier retreated by 1.3 km (0.81 mi).[26] There is evidence that theequilibrium line altitude has risen above the volcano.[27] Some smaller ice fields around Sollipulli either shrank between 1986 and 2017 or disappeared altogether.[28] The process of glacier retreat is probably accelerated by ash being deposited on the glacier through eruptions at the neighbouring volcanoPuyehue-Cordón Caulle; activity at the other volcanoesLlaima andVillarrica may have the same effect.[25] In 2011, the volume of the glacier was 4.5 ± 0.5 km3 (1.08 ± 0.12 cu mi).[8] Melting of the glacier risks generatinglahars and putting water supplies in the region into jeopardy.[25]
Subduction has been ongoing on the western side ofSouth America since 185 million years ago and has resulted in the formation of the Andes and volcanic activity within the range. About 27 million years ago, theFarallon Plate broke up and the pace of subduction increased, resulting in increased volcanic activity and a temporary change in the tectonic regime of the Southern Andes.[9]
Sollipulli volcano developed on a 600-to-1,600-metre-high (2,000–5,200 ft) basement which consists of theJurassic–Cretaceous Nacientes del Biobíoformation and thePliocene-Pleistocene Nevados de Sollipulli volcanics, with subordinate exposures of theMiocene Curamallín and the Cretaceous-Tertiary Vizcacha-Cumilao complex volcano-sedimentary formations.[19] Miocenegranites are intruded into the basement.[29] Two majorfault systems, theLiquiñe-Ofqui Fault Zone and the Reigolil-Pirihueico fault, pass west and east of Sollipulli, respectively. They are connected by east–west trending faults[30] which form agraben at Sollipulli.[31]
Rocks erupted from Sollipulli range frombasalt overbasaltic andesite andandesite todacite. Composition has changed over the evolution of the volcano; sometimes one type of rock is found asinclusion in another.[14] Minerals contained in the rocks includeapatite,clinopyroxene,ilmenite,olivine,orthopyroxene,plagioclase andtitanomagnetite.[32]Xenoliths are also found, includingdiorite andgranophyre.[33]
The petrogenesis of the Alpehué rocks has been explained with the penetration of more primitive magma into a daciticmagma chamber, which was then subject to magma mixing. The primitive magmas sometimes pass through the flanks of the edifice and form parasitic vents in these cases.[34] Magma storage lasts for several tens of thousands of years.[35] The Alpehué eruption was produced by a magma body separate from that of other Sollipulli eruptions,[36] and which evolved long before the Alpehué eruption.[37]
Obsidian was obtained on Sollipulli and exported over large distances; it has been found as far asArgentina's steppes and northern Chile,[5] and is chemically and in appearance different from obsidian obtained onChaitén volcano. One source has been identified at alava dome on the western side of Sollipulli.[38] A route starting south of Melipeuco leads up on the volcano; this route was used for the transport of obsidian in the 1980s.[5]
Annual precipitation amounts to 2.1 metres per year (6.9 ft/a) and mostly falls between April and September.[24] The region is forested, withdeciduous trees includingNothofagus, withlaurel forests around the lakes of the area and woods consisting ofAraucaria araucana andAustrocedrus chilensis at altitudes exceeding 800 m (2,600 ft).[5] In addition there are opengrasslands calledmallines which were used forgrazing.[38]
Sollipulli was active during thePleistocene andHolocene;[19] the Nevados de Sollipulli are less than 1.8 million years old[16] withargon-argon dating having obtained ages of 490,000 ± 30,000 and 312,000 ± 20,000 years ago.[39] Six separate volcanic units form the edifice; from the oldest to the youngest they are the Sharkfin, Northwest, South, Peak, Alpehué and Chufquén units. The first two may be contemporaneous to the formation of the caldera, or they may predate it.[14] The Sharkfin unit was emplaced in a subglacial environment and later disrupted byfaulting,[40] later units show substantial evidence of having been altered by glaciers.[10] Radiometric dates have been obtained on the Sharkfin unit (700,000 ± 140,000 and 350,000 ± 90,000 years before present), the Northwest unit (120,000 ± 16,000, 120,000 ± 140,000, 110,000 ± 30,000 and 100,000 ± 30,000 years before present) and the South and Peak units (68,000 ± 14,000, 64,000 ± 15,000 and 26,000 ± 5,000 years before present).[39] The caldera is nested within an older and eroded caldera,[19] and some parasitic cones are heavily eroded whereas others appear to be younger.[41]
Pyroclastic flows from Alpehué have been dated to 2,960–2,780 yearsbefore present.[6] The Alpehué unit was emplaced during a largePlinian eruption, which generated a 44 km-high (27 mi)eruption column and ejected about 7.5 km3 (1.8 cu mi) of pumice falls.[10] It is the largest known eruption of Sollipulli[42] and one of the largest volcanic eruption to hit northern Patagonia,[43] but did not severely affect vegetation in the region.[44] Tephra from this eruption has been found in neighbouring lakes[45] and insediment cores from the ArgentinaPampa;[46] layers of tephra identified in abog ofSouth Georgia 3,000 km (1,900 mi) away[47] as well as in anice core atSiple Dome inAntarctica and dated to about 980BCE may be a product of the Alpehué eruption.[48] Alpehué tephra has been used as atephrochronology tool.[49] Pyroclastic flows from the eruption melted the caldera ice sheet, forminglahars[a] that propagated northwest away from Sollipulli.[33]Ignimbrites from this eruption cover surfaces of at least 40 km2 (15 sq mi) around Sollipulli, their volume has been estimated to be about 0.4 km3 (0.096 cu mi). They are brown to grey in colour and unwelded with the exception of part of the ignimbrite that is emplaced within the Alpehué crater.[51] The eruption reached a level of 5 on thevolcanic explosivity index[b][1] and led to changes in regional plant communities.[53][54] Isla 2017 proposed that tephra from the eruption blocked the former outlet ofAluminé Lake into theBiobio River via the Rio Litrán, thus redirecting its flow into the Atlantic Ocean.[55]
Radiocarbon dating at Chufquén has yielded an age of 710 ± 60 years before present.[6] This eruption deposited ash onto the caldera ice, while it is absent from the central parts of the Chufquén valley; either it was removed by a later glacier advance or it landed on a glacier which later retreated.[33] The eruption occurred relatively recently, indicating that Sollipulli is still active.[4] Presently,fumaroles and geothermal phenomena occur at the northwestern foot of Sollipulli.[56]
The 0.2 km2 (0.077 sq mi)[57] Alpehue geothermal field, about 4.5 km (2.8 mi) southwest of Alpehue crater,[24] is unusual among the southern Chilean geothermal fields as it featuresgeysers. It lies within a glacial valley presently traversed by[13] the Allipén River,[23] which has cut a verticalcanyon[58] into the Nevados de Sollipulli volcano, close to the intersection between two faults.[23] Geothermal features include "spouters", geysers,hot springs andmud pools, as well asgeyserite andsinter deposits[58] that form small terrace structures.[57] Geyser columns reach 2.5 m (8 ft 2 in) height when they erupt.[58] The geyser field has a total heat output of about 3.3megawatts[59] and has been active since at least 7,400 years. The deep incision and fractured rocks may facilitate the ascent of geothermal waters.[57]
The substantial ice body in the caldera means that there is a significant risk of mudflows orglacier bursts in the case of renewed activity.[12] Conversely, a retreat of the caldera-filling glacier might facilitate the onset ofexplosive eruptions at Sollipulli.[60] A repeat of the Alpehué eruption would be a regional catastrophe, comparable to the 1991 eruption ofCerro Hudson volcano.[61]
The Chilean geological serviceSernageomin monitors the volcano and publishes a hazard index for it. The towns of Cunco, Melipeuco and Villa García are close to the volcano.[3] Melipeuco has devised a Volcanic Emergency Plan to deal with future eruptions of Llaima or Sollipulli.[62]
