| Melimoyu | |
|---|---|
 Oblique view of Melimoyu from theInternational Space Station | |
| Highest point | |
| Elevation | 2,400 m (7,900 ft)[1] |
| Prominence | 2,272 m (7,454 ft)[2] |
| Coordinates | 44°04′33″S72°51′36″W / 44.07583°S 72.86000°W /-44.07583; -72.86000[2] |
| Geography | |
  Melimoyu | |
| Parent range | Andes |
| Geology | |
| Mountain type | Stratovolcano |
| Last eruption | 200 CE ± 75 years[3] |
Melimoyu is astratovolcano (Mapudungunmeli="four";[4] the name means "four breasts".[5]) in Chile. It is an elongated volcanic complex that contains two nestedcalderas of 1 kilometre (0.62 mi) and 8 kilometres (5.0 mi) width. Anice cap has developed on the volcano with a couple of outletglaciers. Melimoyu has not erupted in recent times, but during theHolocene two large eruptions took place and ejected ash at large distances from the volcano.
Melimoyu is a remote[6] volcano in Chile northwest of the townPuyuhuapi[3] and northeast from theMoraleda Channel inlet.[7] The volcano is about 2,400 metres (7,900 ft) high and 10 kilometres (6.2 mi) long,[6] with an elongated shape.[1] There are four summits, all principally created byphreatomagmatic activity[8] and which conspicuously rise above the surrounding area and give the mountain its name.[5] It is one of the larger volcanoes in the region.[9] It bears anice-filled summitcaldera[7] 1 kilometre (0.62 mi)[10]-1.5 kilometres (0.93 mi)[11]-1 kilometre (0.62 mi) wide[1] as well as another, 8 kilometres (5.0 mi) wide caldera that is drained northeastward through a gap in the caldera rim.[3] The volcano is mostly formed bylava flows and has a volume of about 142 cubic kilometres (34 cu mi),[12] which is comparatively large.[10]
Melimoyu displays a largeice cap which after shrinkage over the preceding few decades covered a surface area of 55.59 square kilometres (21.46 sq mi)[13] through a retreat rate of about 0.61 square kilometres per year (0.0075 sq mi/Ms) between 1970-2017;[14] said shrinkage also led to the retreat of outletglaciers and the development of aproglacial lake.[13] There are sixteen[11] or seven glaciers on the mountain, clockwise from north they are named Glaciar Correntoso, Glaciar Melimoyu Este, Glaciar Marchant, Glaciar Melimoyu Sur, Glaciar Melimoyu Oeste, Glaciar Santo Domingo and Glaciar Anihue.[15]
This volcano together withChaiten,Michinmahuida,Corcovado,[6]Yanteles,Macá,Cay andHudson is one of the volcanoes in theSouthern Volcanic Zone which have been active during theHolocene and producedtephra deposits in the region.[9] Volcanic activity in this 1,400 kilometres (870 mi) long volcanic belt is a result of thesubduction of theNazca Plate beneath theSouth America Plate.[1]
The majorLiquiñe-Ofqui Fault Zone has determined the position of a number of volcanic centres; it is astrike-slip fault that accommodates part of the relative movement between the Nazca and South America Plate.[16] The position of Melimoyu is further controlled by a localfault system that runs parallel to the Liquiñe-Ofqui Fault, the Yanteles-Mentolat fault. Aside from Melimoyu, the volcanoesMentolat andYanteles, the Puerto Bonitohot springs as well as localbays andestuaries are influenced by this fault system.[17] Beyond tectonic and volcanic phenomena, thePatagonian Ice Sheet has been active in the region, leaving lakes andfiords.[11]
Tephras from Melimoyu range frombasalt overandesite todacite.[1] They containphenocrysts ofplagioclase plusclinopyroxene andorthopyroxene,[9] but alsohornblende,olivine andquartz[18] and less commonamphibole andbiotite.[12]
The climate at Melimoyu is cold andoceanic, withcold fronts fromAntarctica, westerly winds andsynoptic systems from thePacific Ocean dominating the climate. Summers are short and cold and there is abundant precipitation with nodry season; whereorographic enhancement occurs precipitation can reach 5 metres per year (200 in/year). Average temperatures are about 9.5–9 °C (49.1–48.2 °F).[19]
Two largeHolocene eruptions have been identified at Melimoyu, called MEL1 and MEL2[1] and whose deposits are known as the La Junta and Santa Ana tephras respectively.[10] The larger MEL1 eruption occurred between 2,790 – 2,740 years ago and produced a layered basaltic-dacitic tephra consisting ofpumice with lithics andscoria inclusions.[1] The MEL2 eruption took place about 1,680 ± 100calibrated radiocarbon years ago[9] and consists of pumice[18] ofandesitic composition.[1] MEL1 deposits have thicknesses of 130–30 centimetres (51–12 in) depending on the layer at 30 kilometres (19 mi) distance of the volcano, while MEL2 units rech thicknesses of 50 centimetres (20 in) at the same distance.[18]
AtPalena Lake 115 kilometres (71 mi) east from Melimoyu the MEL1 layer is still 12 centimetres (4.7 in) thick.[6] A 6 centimetres (2.4 in) thick tephra deposit at Lago Shaman and Mallín El Embudo in theRío Cisnes valley has been attributed to the MEL2 eruption.[9] Other findings of tephra are MEL2 layers at Laguna Junco and Laguna Las Mellizas.[12] Overall, both eruptions appear to have had avolcanic explosivity index of 5[20] and produced about 2.6 cubic kilometres (0.62 cu mi) and 1.6 cubic kilometres (0.38 cu mi) tephra for the MEL1 and MEL2 eruption, respectively. The compositions of the two tephras are different, with the MEL2 magma having formed possibly from leftover MEL1 magma. The MEL1 tephra is ofbasaltictrachyandesite tobasaltic andesite composition and the MEL2 tephra is oftrachydacite composition.[21]
Other eruptions identified through tephra at Lago Shaman and Mallín El Embudo occurred 4,800 – 4,600calibrated radiocarbon years ago, while alate glacial maximum eruption over 19,670 yearsbefore present produced another 6 centimetres (2.4 in) thick tephra layer in the Río Cisnes valley.[9] Two additional tephra layers, 8,300 and especially one 19,700 years old, at Río Cisnes may also have originated at Melimoyu[10] and deposits from the latter eruption may also be preserved in the Ñirehuao valley.[22]Glacial activity has otherwise removed much of the record of volcanic activity before the post-glacial.[1][23]
A 350 ± 200CE eruption at Melimoyu deposited ash as far asAntarctica, where it was found in theSiple Dome.[24] This eruption together with volcanic eruptions ofCalbuco andTaupō inNew Zealand induced noticeable cooling and increased snowfall inAustralia.[25] There are no recorded historical eruptions[1] aside from occasionalseismic events.[7]
TheChaiten eruption in 2008 has highlighted the hazard that volcanoes constitute, and thus a number of volcanoes including Melimoyu are monitored withseismic stations.[26] Local towns such asPuerto Cisnes may experience tephra falls in case of renewed volcanic activity at Melimoyu,[12] whilelahars andlava bombs would threaten the area directly surrounding the volcano.[7]