| Quetrupillán | |
|---|---|
 Quetrupillán with Lanín in the background | |
| Highest point | |
| Elevation | 2,360 m (7,740 ft) |
| Coordinates | 39°30′S71°42′W / 39.5°S 71.7°W /-39.5; -71.7[1] |
| Geography | |
 | |
| Location | Chile |
| Parent range | Andes |
| Geology | |
| Rock age | Pleistocene-Holocene[1] |
| Mountain type | Stratovolcano |
| Volcanic zone | South Volcanic Zone |
| Last eruption | June 1872[1] |
| Climbing | |
| Easiest route | Palguín - Laguna Azul |
Quetrupillán ("blunted", "mutilated";[2] also known as Ketropillán;[2] the name is sometimes applied to the neighbouringLanín volcano.[3]) is astratovolcano located inLos Ríos Region ofChile. It is situated betweenVillarrica andLanín volcanoes, withinVillarrica National Park. Geologically, Quetrupillán is located in a tectonic basement block between the main traces ofLiquiñe-Ofqui Fault (to the west) andReigolil-Pirihueico Fault (to the east).
The volcano consists of onestratovolcano with a summitcaldera, and is constructed within a field of smaller centres and a larger caldera. It was active during the latePleistocene; some large eruptions occurred during theHolocene as well.
The volcano is situated in theCurarrehue,Pucón andPanguipullimunicipalities of theCautín andValdivia provinces. Towns close to Quetrupillán are Catripulli, Currarehue and Puesco. It is considered Chile's 21st most dangerous volcano.[4] The volcano and its neighbours form part of theKütralkurageopark[5] and are an importanttourism destination.[6]
Off the western coast of South America, theNazca Platesubducts beneath theSouth American Plate in thePeru-Chile Trench. As the plate subducts, it releases water into the overlyingmantle and causes it to melt, gives rise to theSouthern Volcanic Zone of the Andes. The rate and geometry of subduction has varied over time. During the last six million years, the subduction process has been oblique and as a consequence, theLiquiñe-Ofqui Fault has developed within thevolcanic arc and dominates the regional tectonics.[7]
Quetrupillán lies on the border betweenLos Ríos Region andAraucanía Region,[4][8] in theSouthern Volcanic Zone.[8] Together withVillarrica andLanín it forms a northwest-southeast alignment of volcanoes,[8] which coincides with the Mocha-Villarricatranscurrent fault.[9] The Cordillera El Mocho and Quinquilil volcanoes are likewise situated on this alignment,[10] both are deeply eroded composite volcanoes of small dimensions.[11] Other volcanoes in the Southern Volcanic Zone have similar alignments, such asNevados de Chillán andPuyehue-Cordón Caulle.[10] In comparison to Villarrica, Quetrupillán has been less active and its eruptions were also smaller than Villarrica's,[12] with no largepyroclastic flows found at Quetrupillán.[11]
Quetrupillán is a 2,360 metres (7,740 ft) high compositestratovolcano[11] and a shrinkingglacier cover;[13] the existence ofcalderas is unconfirmed.[14] The entire edifice has a north-south elongated shape[15] and covers a ground surface of 107 square kilometres (41 sq mi).[4] The volcano contains a field oflava domes,maars andpyroclastic cones that occupy a surface of 400 square kilometres (150 sq mi).[16][11] These subsidiary vents include the scoria cone Huililco, the Volcanes de Llancahue and the Volcanoes de Reyehueico.[1] There are in total 16 lateral vents, of which 12 are found in avolcanic field south of Quetrupillán.[16]Fissure vents ofPleistocene-Holocene age occur on the southern side of the volcano. The small volume of the main Quetrupillán edifice and the widespread vents may reflect the interaction between the volcano and the Liquiñe-Ofqui fault, which generated secondary vents[17] whose location was controlled by the Liquiñe-Ofqui fault, the Mocha-Villarrica fault and local structures.[18] There are two lakes on the southern flank, Laguna Azul to the southwest and Laguna Blanca to the southeast.[14]
A number of eruption products show traces of ice-lava interactions.[17]Tuff rings and maars formed through the interaction of magma withgroundwater.[16] Ageomagnetic anomaly at shallow depth south of the volcano may be apluton associated with aresurgent dome.[19] Huililcoscoria cone has produced two lava flows and is considered to be also part of the Quetrupillán volcanic complex.[20]
Three differentformations make up thebasement of Quetrupillán: TheTriassic Panguipulli, the possiblyCretaceous Currarehue and theMiocene Trápatrapa formations andplutonic rocks.[10] These are plutonic andvolcaniclastic rock units.[20] The Villarrica-Quetrupillán volcanic chain forms a geological boundary, since thePatagonian Batholith crops out south of it.[21]Magnetotelluric investigation of the area has found evidence of a possible deep-seated magma reservoir.[22]
Volcanic rocks at Quetrupillán have a bimodal composition,[23] ranging frombasalt toandesite[11] withtrachyte the main component,[24] and overall more silicic than the rocks erupted by Villarrica and Lanín.[1] Unusually for the region,trachydacite also occurs at the volcano. These containphenocrysts ofplagioclase andpyroxene, with additional microphenocrysts ofilmenite andmagnetite.[25]
Based on the composition, it has been inferred that the magma reservoir of Quetrupillán contained a mush of crystals, from which magma was repeatedly mobilized following the injection of fresh magmas that reheated the mush.[25]Fractional crystallization of basalts generatedtrachytic melts.[20] A tectonic regime associated with the Liquiñe-Ofqui Fault which prevents magma from simply ascending to the surface may help the magma evolution processes.[26]
Eruptive activity at Quetrupillán commenced before theice ages. The first phase of activity involved the formation of calderas and stratovolcanoes; later during the ice ageslava flows andignimbrites were emplaced. Finally, the presentstratovolcano was emplaced towards the end of glaciation;parasitic vents formed even later[11] and produced lava flows.[20]
Quetrupillán has eruptedpyroclastics, which have formed flow andpumice deposits east of the volcano. Several phases of volcanic activity have been inferred from the deposits; most of them feature eitherpumiceous orscoriaceouspyroclastic flow deposits with varying contents of juvenilelapilli,lithics and ash fall deposits.[8]
In addition, threetephras in neighbouring lakes dated to 16,748–16,189, 15,597–12,582 and 12,708–12,567 years Before Present may originate from Quetrupillán but they have also been attributed toSollipulli. All these tephras are ofrhyolitic torhyodacitic composition and the eruptions that generated them have an estimatedvolcanic explosivity index of 3.[28]
Reports exist of eruptions during the 19th century,[11] one eruption was reported in 1872.[1] Explosive activity has a recurrence interval of about 1,200 years, which given the age of the last event carries significant implications with regards to the volcanic hazard of Quetrupillán.[12]
According to a tale fromMapuche mythology, originally there were just two volcanoes:Choshuenco andLanín. Then the volcanoRuka Pillan (Villarrica) fought the other two volcanoes in a century-long conflict; eventually Ruka Pillan was victorious, coinciding with the beginningSpanish conquest.[29]
Annual precipitation exceeds 1,800 millimetres (71 in), with a mean annual temperature of 7.5 °C (45.5 °F). The slopes of Quetrupillán are covered bytemperate forests, withNothofagus trees being the most important species; other trees are thetepa and themaniú hembra.[30] As of 1961[update], vegetation on Quetrupillán includedAraucaria araucana andNothofagus antarctica forests, as well aspuna-like vegetation.[31]
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