Mount Hudson
Cerro Hudson
Aerial photo from 1991
Highest point
Elevation1,905 m (6,250 ft)
Coordinates45°54′S 72°58′W / 45.900°S 72.967°W / -45.900; -72.967[1]
Naming
EtymologyNamed after Francisco Hudson
Geography
LocationChile
Parent rangeAndes
Geology
Mountain typeStratovolcano
Volcanic arc/beltSouthern Volcanic Zone
Last eruption2011

Mount Hudson (Spanish: Volcán Hudson, Monte Hudson) is a volcano in rugged mountains of southern Chile. Lying in the Southern Volcanic Zone of the Andes, it was formed by the subduction of the oceanic Nazca Plate under the continental South American Plate. The Nazca Plate ends there at the Chile Triple Junction; south of Hudson is a smaller volcano then a long gap without active volcanoes. Hudson is a large volcanic caldera, formed partly by non-volcanic rocks and largely filled with ice. The Huemules Glacier emerges from the northwestern side of the caldera. The volcano has erupted rocks ranging from basalt to rhyolite.

In the late Pleistocene and Holocene, Hudson has erupted numerous times. Four large eruptions took place 17,300-17,440 (H0), 7,750 BP (H1), 4,200 BP (H2) and in 1991 AD (H3); they are among the most intense volcanic eruptions in South America. A smaller eruption took place in 1971. The 7,750 BP and 1991 eruptions had a substantial impact on human populations of Patagonia and (for the 7,750 BP eruption) Tierra del Fuego: The 7,750 BP eruption devastated its ecosystem and may have caused substantial shifts in human settlement and lifestyle. During the 1991 eruption, volcanic ash covered a large area in Chile and neighbouring Argentina, causing high mortality in farm animals, aggravating an existing economic crisis, and depositing ash as far as Antarctica. The last eruption was in 2011.

Geography and geomorphology

Mount Hudson lies in Andes of southern Chile,[2] in the Aysen Province[a][4] northwest of Lago Buenos Aires.[5] Another name is Cerro de los Ventisqueros,[4] which is technically the correct name of the volcano as "Hudson" is the name of a different mountain.[6] The name "Hudson" refers to Francisco Hudson a Chilean Navy captain and hydrographer.[7] Owing to its remoteness and the dense vegetation at its foot, the volcano is poorly studied;[8] it was recognized as a volcano only[b] in 1970.[12] The closest cities are Puerto Aysen 58 kilometres (36 mi) north-northeast and Coihaique 75 kilometres (47 mi) northeast; the Carretera Austral highway passes 30 kilometres (19 mi) from the volcano.[2] The volcano can be accessed either from the sea through the Huemules River or by land through the Blanco River from Lago Elizalde-Lago Claro.[13]

The Andean Volcanic Belt includes four volcanic zones separated by gaps without recent volcanoes. From north to south they are the Northern Volcanic Zone, the Central Volcanic Zone, the Southern Volcanic Zone (SVZ) and the Austral Volcanic Zone.[14] Hudson is the second-southernmost volcano[c] of the SVZ, after Rio Murta.[16] Farther south is the 350 kilometres (220 mi) long[15] Patagonian Volcanic Gap[17] in the Andean Volcanic Belt, then the Austral Volcanic Zone.[15] The next volcanoes to the north are Mate Grande 35 kilometres (22 mi)[18] and Macá and Cay 95 kilometres (59 mi) from Hudson,[19] then Mentolat and the Puyuhuapi volcanic field.[5]

The volcano is a 10 kilometres (6.2 mi) wide ice-filled caldera that rises 1,000–1,200 metres (3,300–3,900 ft) above the surrounding terrain.[19] It appears to consist of two nested calderas.[20] Only the western and southern margins are well defined.[21] Their highest point reaches 1,905 metres (6,250 ft) elevation.[2] The edifice consists partly of volcanic rocks and partly of uplifted basement,[22] and covers an area of about 300 kilometres (190 mi). The edifice has an eroded appearance,[19] with steep valleys cutting as much as 1 kilometre (0.62 mi) into the outer reaches of the volcano.[2] The total volume of the volcano is about 147 cubic kilometres (35 cu mi), larger than other SVZ volcanoes.[23] Cinder and spatter cones reach heights of 200–300 metres (660–980 ft) and are sources of lava flows outside of the caldera, especially in the Sorpresa Sur valley.[24] There are two cones northeast of the caldera and one in the far southwest.[25] The landscape of the Andes around Hudson is formed by numerous mountains (including the Cerros Hudson 12 kilometres (7.5 mi) south of the volcano) with deep, glacially carved valleys.[2] Thick volcanic soils occur in the area.[26]

The caldera is filled with about 2.5 cubic kilometres (0.60 cu mi) of 40 metres (130 ft) thick ice,[27] forming an ice surface at about 1,505–1,520 metres (4,938–4,987 ft) elevation. Ice flows out of the northwestern margin of the caldera and forms the Ventisquero de los Huemules Glacier.[19] The Huemules Glacier is the largest glacier of Mount Hudson, being 11 kilometres (6.8 mi) long,[19] and the headwater of the Huemules River. The glacier is covered by tephra and its surface has too low an altitude for the tephra to be buried under snow;[28][29] thus from the air the glacier looks like a lava flow.[24] A small crater lake is at its beginning and occupies a crater of the 1991 eruption.[24] Most of the ice in the caldera was destroyed by the 1971 eruption, but by 1979 had built back up again. During the 1991 eruption, cones surrounded by crevasses and small lakes formed in the ice. The recovery of the ice after the 1991 eruption was slower, and by 2002 Huemules was retreating.[30][29] During eruptions, pyroclastic material and lava can melt the ice.[31] Other glaciers emanating from the ice cap are the Desplayado, Bayo, Ibáñez, El Frio, Sorpresa Sur and Sorpresa Norte glaciers. They were up to 3 kilometres (1.9 mi) long in 1974 but have retreated since then.[19] Together with the Queulat Ice Cap, the Hudson glaciers make up a large part of the regional glacier inventory,[32] and have left well-preserved moraines.[33] The path of some of the glaciers may be influenced by local tectonic lineaments.[13] Numerous rivers originate on Hudson; clockwise from north to south they include the Rio Desplayado to the north, the Rio Bayo to the east, the Rio Ibáñez, the Rio Sorpresa Sur, Rio Sorpresa Norte all to the southeast, and the Huemules river to the northwest.[2] Volcanic activity might be responsible for fluctuations in the discharge of the Huemules river.[4]

Geology

Off the western coast of South America, the Nazca Plate subducts beneath the South America Plate at a rate - at Hudson's latitude - of about 9 centimetres per year (3.5 in/year).[14] This subduction is responsible for volcanism in the SVZ[8] and the rest of the Andean Volcanic Belt[14] except for the AVZ, where the Antarctic Plate subducts instead.[15]

West of Hudson and the Taitao Peninsula,[14] the Chile Ridge enters the Peru-Chile Trench, forming the Chile Triple Junction. The subduction of the ridge has produced a slab window in the downgoing slab, causing volcanism to cease in the Miocene and a gap to open up between the SVZ and the AVZ.[8] The collision began 14 million years ago; since then, the triple junction[14] and the volcanic gap are migrating north.[8] Several fracture zones cut through the downgoing plate,[14] one of which may project under Hudson;[34] the Tres Montes Fracture Zone to its south that forms the northern boundary of the slab window.[35] The subducted plate is still young and hot.[36] The position of Hudson just east of the triple junction may be responsible for its unusually high activity.[37]

Older volcanism in the region includes back-arc volcanoes in Patagonia and adakitic rocks in the Taitao Peninsula that were emplaced during the last 4 million years.[38]

Hudson rises from the Patagonian Batholith, a 1,000 kilometres (620 mi) long formation made up by intrusive rocks (diorite, gabbro, granite, granodiorite and tonalite[19]) that was emplaced during the Cretaceous-Neogene.[28] The crust under the volcano is about 30 kilometres (19 mi) thick.[39] The volcanism in the SVZ is heavily influenced by faults, including the Liquine-Ofqui Fault Zone (LOFZ) that runs parallel to the volcanic belt.[40] In the Hudson area, the LOFZ is formed by two branches connected through perpendicular faults[35] and lies 30 kilometres (19 mi) west of the volcano.[9] The LOFZ moves at a rate of about 1–2 centimetres per year (0.39–0.79 in/year) in the area.[41] Recently active faults around the volcano can be recognized in the vegetation.[42]

Composition and magma plumbing system

Hudson has erupted a wide range of volcanic rocks.[43] The cones outside the caldera have produced basaltic andesite and andesite.[22] The Hudson rocks define a potassium-rich calc-alkaline rock suite straddling the alkaline-subalkaline line.[44][45][46] Rocks contain only few phenocrysts,[22] including andesine, apatite, clinopyroxene, ilmenite, oligoclase, olivine, orthopyroxene, plagioclase and titanomagnetite.[47] The composition of Hudson rocks diverges from that of other SVZ volcanoes,[48] with higher concentrations of iron oxide, sodium oxide, titanium oxide and incompatible elements.[9]

The cone lavas includie MORB and ocean island basalt components as well as crust- or sediment-derived components,[49] while the caldera magmas formed through fractional crystallization[d],[50] possible along with the assimilation of crustal material.[51] The three major Holocene eruptions produced uniform magmas with temperatures of 943–972 °C (1,729–1,782 °F), a few percent water by weight and a trachyandesitic to trachydacitic composition.[52] The H2 eruption led to a change of magma chemistry to more mafic compositions, followed by a reversal during the last 1,000 years.[53]

Magma genesis processes can be complex in slab window areas, as melts derived from the asthenosphere that ascended through the window can take part.[8] Magmas ascending into Hudson halt at about 6–24 kilometres (3.7–14.9 mi) depth and undergo a first phase of differentiation. Later the magma ascends into shallower reservoirs[54] and is then stored at a few kilometres depth before the large Holocene eruptions.[52] During historical eruptions, the vents opened up in the southwestern sector of the caldera.[55] Some magmas can bypass the magma chamber and directly ascend to the surface through faults, forming the volcanic cones surrounding Hudson.[56]

Climate and vegetation

The climate at Hudson is oceanic, with mean annual temperatures of 8–10 °C (46–50 °F). Precipitation at the coast reaches 3 metres (9.8 ft) per year, increasing to 10 metres (33 ft) in the Andes and declining to 800 millimetres (31 in) in the eastern valleys.[57][58] Precipitation is brought by westerly winds and enhanced on the western slopes of the Andes by orographic precipitation, while the eastern slopes are within the rainshadow.[59] Winds usually blow from the north or northwest and are strong, easterly winds are rare.[57][58]

The region is covered by temperate rainforests formed by conifers, broadleaf trees and beeches (Nothofagus pumilio).[57][58] Magellanic moorlands with cushion plants occur in the coastal areas. To the east there is a transition to the Patagonian steppe with grasses, herbs and scrubs. Since the 19th century, the vegetation has been altered by human intervention.[60]

Eruption history

Hudson has been active for more than one million years.[9] The northeastern sector of the volcano is older than the southeastern, which has yielded ages of 120,000-100,000 years,[61] but the incomplete stratigraphy of the edifice, which is largely covered with ice, precludes establishing a proper history of its growth.[62] There are few tephras from the Pleistocene-Holocene transition time close to the volcano, but several have been found in marine cores west of Hudson.[63]

During the last glacial maximum, Hudson was at the centre of a large ice sheet that covered the entire region.[64] Tephra from its eruptions fell on the ice and was carried away by glaciers, ending up in their moraines.[65] Beginning 17,900 years ago,[5] the deglaciation may have enhanced volcanic activity, explaining why the volumes of the intense Hudson eruptions have decreased over time.[66] On the other hand, glaciation has removed most of the volcanic record of Patagonia pre-dating 14,500 years ago.[67]

Holocene

Numerous explosive eruptions took place during the Holocene,[68] including three intense eruptions[15] among the largest of Holocene South America.[39] There is a regularity, with intense explosive eruptions occurring about every 3,870 years,[68] but their volumes have decreased over time and erupted rocks have grown less mafic.[50] Smaller Plinian eruptions occur about every 500-1000 years.[69] With more than 55 eruptions during the past 22,000 years,[37] Mount Hudson is the most active volcano in Patagonia[e].[11]

The Hudson caldera probably formed during the Holocene and grew incrementally.[22] Pre-caldera outcrops are rate and consist of breccias formed by hyaloclastite, lahars, mafic lavas and pyroclastic rocks; they occur mostly on the northeastern and southern side of the caldera.[28] Outside of the caldera, especially south, are widespread pyroclastic fall deposits formed by banded pumice. Lahar deposits contain blocks of lava embedded within a fine-grained substrate.[24] One ignimbrite probably associated with the formation of the caldera occurs all around Hudson. A Holocene lava flow extends along the Huemules valley and is 1–5 metres (3 ft 3 in – 16 ft 5 in) thick.[20] Argon-argon dating has yielded an age of 13,000 years.[61] The volcanic cones outside of the caldera are weathered and covered by vegetation; they are also of Holocene age.[20] Other geologic processes like glacial erosion have modified the appearance of the Hudson volcano.[70]

Pyroclastic fall and tephra deposits[8] from Hudson and other volcanoes have been identified in marine cores in the Pacific Ocean, sediments in lakes and peat bogs,[71] in soils,[68] and potentially in Antarctic ice cores.[72] Such tephra layers can be used to compare the timing of events across wide regions.[58] Tephra particles from Hudson have varying shapes and colours, but similar compositions.[73] The closest tephra record to Hudson is the Laguna Miranda record 50 kilometres (31 mi), which shows on average one tephra layer every 225 years although it only records eruptions that distributed ash in the direction of the lake.[74] Several Hudson tephra layers from Juncal Alto 92 kilometres (57 mi) have been named T1 through T9,[75] and another set from lakes in the Chonos Archipelago and Taitao Peninsula is named HW1 through HW7.[76]

Selected tephra layers from Hudson
Date BP[f], margins of error omitted Taitao marine core tephra[77] Chonos Archipelago lacustrine tephra[78] Juncal Alto[75] tephra layers[79] Notes
19,860 TL12
19,660 TL11
19,600 TL10
19,450 TL9
18,900 TL8
18,750 TL7
17,350 TL6
16,100/14,560 TL5[77] HW1[77]
14,110/13,890 TL4[77] HW2[77]
12,000/11,060 TL3[77] HW3[77]
10,750 TL2 Tentatively assigned to Hudson[77]
6,910 T1
6,700/7,540 HW4 T2 H1 eruption[80][79]
5,840 T3
4,200 T4
3,840 HW5 T5 H2 eruption[79]
2,740 HW6 Also found southeast of the volcano[81]
2,070 T6 Also found in the Talos Dome, Antarctica[82][83]
1,920/1,560 TL1[77] HW7[77] The attribution of a tephra layer in the Talos Dome of Antarctica is questionable[84]
1,090 T7
210 T8
-21 (1971 AD) T9

An uncertain eruption occurred 8010 BC.[79] Tephra layers from 1035 CE[85] and 9,216 BC in the Siple Dome of Antarctica have been attributed to Hudson, but for the older eruption there is no evidence in South America of an appropriately sized event.[86] The Las Guanacas cave 100 kilometres (62 mi) southeast of Hudson preserves an over 10,000 years old ash from Hudson. On the Taitao Peninsula, tephra layers have been attributed to two eruptions in 11,910 and 9,960 years before present. These are isolated occurrences, indicating that they are not the products of very intense eruptions that could be expected to leave widespread deposits.[87] Westward spread of Hudson tephras was more common in the earliest Holocene, when the Southern Hemisphere westerlies were located north of Hudson.[88]

Significant eruptions and recent activity

H0 eruption: 17,300-17,440 BP

The H0 eruption took place between 17,440-17,300 BP[89] during late glacial times.[15] It is the largest known eruption of Hudson, yielding more than 20 cubic kilometres (4.8 cu mi)[g] of tephra, and may have initiated the growth of the caldera.[91] The eruption occurred during deglaciation and was probably caused by the unloading of the magmatic system, when the overlying ice melted.[92] The eruption occurred in several stages that yielded distinct rock compositions,[93] and like the 1991 AD eruption includes two distinct chemistries.[46] Basalt and trachyandesite were the dominant components.[50]

The tephra was emplaced northeastward, with thicknesses exceeding 50 centimetres (20 in) up to present-day Coihaique and the border with Argentina.[94] Tephra from the H0 eruption has been found in Lago Churasco, Lago Élida, Lago Mellizas, Lago Quijada, Lago Toro, Lago Shaman and Lago Unco northeast of Hudson.[95] After the eruption had ended, winds redeposited the tephras over distances of 400 kilometres (250 mi).[96]

H1 eruption: 7750 BP

The largest Holocene eruption of Hudson - and any volcano of the southern Andes - took place at Hudson in 7750[h] BP,[98] and is known as the H1 eruption.[68] It produced about 18 cubic kilometres (4.3 cu mi) of trachydacitic or trachyandesitic rocks,[22][99][50] thus reaching a volcanic explosivity index of 6.[100] A mass wasting deposit in the Aysen Fjord and the ignimbrite surrounding Hudson probably came from this eruption.[101][62] The tephra deposits have three layers, an intermediary aggregate lapilli formed through phreatomagmatic activity from a tall eruption column, and two overlying and underlying layers of pumiceous lapilli.[102] Water, presumably from glaciers and permafrost on the volcano, drove the phreatomagmatic activity.[103] Water interaction was more intense during H1 than during the H2 and H3 eruptions, which may imply that the caldera collapse occurred during this eruption, causing effective magma-ice interaction.[104]

Ash from the H1 eruption fell south-southeast from the volcano, extending over all of southern Patagonia[105] and part of Magallanes.[97] It has been recovered from lakes like Lago Cardiel and Laguna Potrok Aike, peat bogs including at Puerto del Hambre and Punta Arenas, and archaeological sites.[106] More distant sites include Isla de los Estados[107] and Siple Dome in West Antarctica.[108] The Patagonian-Tierra del Fuego Tephra II originated in this eruption.[68] The wide dispersal of the ash was either due to the eruption column exceeding 55 kilometres (34 mi) height or due to strong winds.[100] Similar to the 1991 eruption, the H1 eruption would have buried food and water resources and caused various health ailments.[109] This would have caused a collapse of the terrestrial ecosystems in Patagonia,[110] possibly causing a lasting shift of guanaco populations,[111] a population shift at Cueva de las Manos,[112] and the extinction of human mitochondrial DNA lineages.[113] More controversially,[114] the eruption may have caused a cessation of the southern Patagonian obsidian trade,[115][116] and a shift towards the use of coastal resources by people in Patagonia.[117]

Impact on Tierra del Fuego

The green-brown tephra deposits in Tierra del Fuego were produced by this eruption.[98] On Tierra del Fuego, the H1 tephra covers an area exceeding 40,000 square kilometres (15,000 sq mi).[118] Thicknesses reach 4–20 centimetres (1.6–7.9 in),[105] thicker than deposits closer to the volcano.[119]

The H1 eruption had a severe impact on the environment of Tierra del Fuego, with the vegetation being buried by ash fall.[120][121] Impact on human populations in Tierra del Fuego would have been severe,[68] possibly causing the total extinction of hunter-gatherers on Tierra del Fuego[110] or even of all human life on the island.[122] Vertebrates were decimated and large mammals wiped out.[123] After the eruption, activities at the Túnel 1 archaeological site changed from a terrestrial lifestyle to one that relied on coastal foodsources[124] which were less vulnerable to volcanic impacts.[125] The island may have been resettled over a millennium later by people arriving through bark canoes. These immigrants reintroduced mammals like guanacos on the island.[126]

H2 eruption: 4200 BP

The H2 eruption occurred about 4200 years[i] ago. Pumices form three or four distinct layers, which consist mostly of trachydacite/trachyrhyolite.[127][128][102][50][99] The eruption was smaller than the H1 eruption, but larger than the H3, reaching a volcanic explosivity index of 6.[128] It or neoglacial climate change may have caused changes in the vegetation close to the volcano.[129]

Ash layers have been found at various sites close to the volcano, with cryptotephra reaching the Falklands.[130][127] The occurrence at Lago Quijada is the reference section for the H2 eruption.[131] Unlike the H1 and H3 eruption, the H2 ash was dispersed mainly to the east and at larger distances to the southeast, forming a wider deposit.[127][128] It has been identified in the Los Toldos, Cerro Tres Tetas and La María archaeological sites;[127] evidence at the Los Toldos archaeological site indicates that humans left the area after the H2 eruption.[132]

H3 eruption: 1991 AD

The 1991 Plinian eruption was larger than the 1971 event[8] and is known as the H3 eruption.[9] After a few hours of seismic activity, a phreatomagmatic eruption commenced on August 8 at 18:20 in the northwestern sector of the caldera.[133] The phreatomagmatic phase formed a 4 kilometres (2.5 mi) long fissure and a 400 metres (1,300 ft) wide crater. On August 12, a Plinian eruption formed a 800 metres (2,600 ft) wide crater in the southwestern sector. The eruption continued for the following three days.[9] Seismic and fumarolic activity continued for the next months,[134] and small eruptions may have occurred in October.[135]

The initial phreatomagmatic eruption was basaltic.[135] The chemistry of the erupted rocks changed during the course of the eruption from trachyandesite to trachydacite,[68] perhaps due to fractional crystallization of phenocrysts or amphibole and magma mixing.[136] Initially, basaltic magma rose in the edifice and entered a trachyandesitic reservoir at 2–3 kilometres (1.2–1.9 mi) depth, until the stresses opened up another pathway along local-scale fractures. This formed the northwestern vent and associated lava flows. Later, the roof of the reservoir failed, allowing the trachyandesitic magma to ascend to the surface and form the southwestern vent.[137] The eruption may have been triggered by tectonic stress changes caused by the 1960 Valdivia earthquake.[138]

The eruption is the second-largest historic volcanic eruption in Chile, only behind the 1932 Quizapu eruption.[21] With a volcanic explosivity index of 5,[139] it is one of the largest volcanic eruptions of the 20th century.[17] It formed a 12 kilometres (7.5 mi) high eruption column and pyroclastic flows within the caldera.[140] A 4 kilometres (2.5 mi) long lava flow was emplaced on the caldera ice and flowed down the Huemules river.[141][142][141] Part of the ice cap melted.[143] A lahar with a volume of about 0.04–0.045 cubic kilometres (0.0096–0.0108 cu mi) ran for 40 kilometres (25 mi) down the Huemules river[144] to its mouth in the Pacific Ocean.[143] Ash deposited by the volcano was eroded by rivers and redeposited in their deltas, enlarging them.[27] Wind-driven erosion of the ash in the semiarid region produced continued ash fall,[145] which was sometimes mistaken for renewed activity,[146] and 1.5 metres (4 ft 11 in) thick wind-blown dust accumulations formed in some areas.[147]

More than 4 cubic kilometres (0.96 cu mi) of tephra fell along two axes: A narrow northern one and a much wider and longer east-southeast trending axis from the volcano in southern Patagonia and the South Atlantic Ocean.[68][17] The northern ash was produced by the phreatomagmatic phase and the southeastern one by the Plinian one.[148] Ash fell over an area of about 150,000 square kilometres (58,000 sq mi) in Chile and Argentina,[21] reaching as far as the Falkland Islands and South Georgia.[149] The ash fall buried vegetation and roads and caused house roofs to collapse. Animals saw their pastures buried and food contaminated by ash, their wools weighed down, and people reported problems with breating and eyesight owing to the irritating ash.[147] Ailments[j] caused by the ash and preceding harsh winter killed about half of all grazing animals in the directly affected areas such as Argentina's Santa Cruz Province,[151] where damage exceeded 10,000,000 dollars.[152] Along with other climatic and economic crises, the Hudson eruption led to a severe depopulation in the region.[153]

Intercontinental spread of ash

Winds transported the plume towards Antarctica and in the westerlies surrounding the polar vortex, circling the continent in a month[154] and reaching Chile again after a week.[27] Ash from the eruption was found in snow at the South Pole, arriving there in December,[155] ice cores of East Antarctica,[156] and in various sites of the northern Antarctic Peninsula, where it arrived in August.[157] Aircraft noted the ash cloud as far as Melbourne in Australia.[27] Particles from Hudson have been found in ice at Mount Everest, Himalaya.[158]

The 1991 eruption of Hudson took place in the same year with the 1991 eruption of Mount Pinatubo.[159] The Pinatubo aerosols had already spread worldwide when Hudson erupted. Unlike the Pinatubo eruption, Hudson mostly produced volcanic ash which fell out more quickly.[155] However, the Hudson cloud led to substantial ozone loss over Antarctica and had comparable effects to the Pinatubo eruption in the southern hemisphere.[160]

Other historical activity

There are reports of historical eruptions in the late 19th century, but only an 1891 eruption can be attributed to Hudson.[161] There are single reports of eruptions in 1930[162] and 1965.[163] A crater in the centre-western sector of the caldera may have been active around 1973.[161] A lahar in that year killed a number of animals and two shepherds; it may either be non-volcanic[164] or due to a subglacial eruption. Other lahars may have occurred in 1972 and 1979.[135]

On the morning of August 12 1971 tremors heralded the onset of a new eruption.[12] It lasted for three days and reached a volcanic explosivity index of 3-4. An eruption column rose 5–12 kilometres (3.1–7.5 mi) above the volcano and deposited tephra to the east into the South Atlantic Ocean.[161] Ashfall buried pastures[6] and left deposits in lakes of the Chonos Archipelago.[165] A lahar descended the Huemules river, killing at least five people and damaging houses and farms.[161] The lahar dragged blocks of ice along,[166] swept the valley clear of trees and produced a pumice raft in the sea off the mouth of the Huemules river.[167] No pyroclastic flows formed during this eruption,[12] while (subglacial) lava flows may[142] or may not have formed.[12]

The last eruption was in October 2011,[9] and was preceded by increasing hydrothermal activity.[168] It was preceded by several days of increased earthquake activity. [169] It began on October 26 and ended on November 1.[79] Three vents formed in the southern sector of the caldera, with ash columns rising to almost 1 kilometre (0.62 mi) altitude.[169] Lahars ran along several valleys surrounding the volcano, probably caused by ice interacting with the hydrothermal system of the volcano.[149] Chilean authorities evacuated about 140 people from the region due to the threat from ash fall and lahars.[169]

Between 1991 and 2008, uplift took place at the volcano. Initially at a pace of 5 centimetres per year (2.0 in/year), after 2004 it decreased to a rate of 2 centimetres per year (0.79 in/year).[170] The uplift was probably caused by the entry of new magma in Hudson's plumbing system.[135] Presently, shallow seismicity takes place under Hudson and south of it, between 0–10 kilometres (0.0–6.2 mi) depth, and is probably related to volcanic activity.[171]

Hazards

The 1991 eruption has drawn attention to hazards stemming from Hudson and other Patagonian volcanoes.[172] About 84,000 people live around Hudson.[173] Despite the low population density in the regions of Argentina downwind of Hudson, ash fall can cause serious impacts on farming and animal husbandry.[152]

After the 1991 eruption of Hudson, the Argentine SEGEMAR initiated a monitoring program for Argentine volcanoes.[174] The Chilean SERNAGEOMIN published a volcano hazard map in 2014, which shows areas threatened by lahars, lava flows, pyroclastic fall, pyroclastic flows, tephra fallout and volcanic bombs.[175] However, as of 2023 the municipal planning of the municipalities on the Chilean side close to the volcano largely ignore volcanic hazards.[176]

Notes

  1. ^ Most of the volcano is in the Chilean municipality of Aysen; the eastern and southern parts are in the municipalities Coihaique and Rio Ibáñez, respectively.[3]
  2. ^ While it is often stated that the 1971 eruption led to its recognition as a volcano,[9] an unpublished report about the caldera was written in 1970.[10][11]
  3. ^ It is often erroneously considered the southernmost.[15]
  4. ^ Including amphibole[34]
  5. ^ Formerly it was thought that it had been largely inactive during the past 10,000 years.[12]
  6. ^ Conversion of BCE to BP by adding 1950, and from AD by subtracting the AD from 1950
  7. ^ Which may be an overestimate.[90]
  8. ^ Older date estimates are 8260[97] or 6700 BP.[22]
  9. ^ Older estimates of its age are 3600[102] or 3920 BP[15]
  10. ^ Not fluorosis, as is commonly reported.[150]

References

  1. ^ GVP 2023, General Information.
  2. ^ a b c d e f Naranjo S., Moreno R. & Banks 1993, p. 6.
  3. ^ Geoffroy & Ciocca 2023, p. 40.
  4. ^ a b c Fuenzalida & Espinosa 1974, p. 1.
  5. ^ a b c Weller et al. 2014, p. 2.
  6. ^ a b GVP 2023, Bulletin Report CSLP 80-71.
  7. ^ Sánchez 1905, p. 33.
  8. ^ a b c d e f g Gutiérrez et al. 2005, p. 208.
  9. ^ a b c d e f g Weller et al. 2014, p. 4.
  10. ^ Fuenzalida & Espinosa 1974, p. 3.
  11. ^ a b Naranjo & Stern 1998, p. 291.
  12. ^ a b c d e Best 1992, p. 301.
  13. ^ a b Fuenzalida-Ponce 1974, p. 79.
  14. ^ a b c d e f Gutiérrez et al. 2005, p. 209.
  15. ^ a b c d e f g Weller et al. 2014, p. 3.
  16. ^ Gutiérrez et al. 2005, pp. 209, 216.
  17. ^ a b c Kratzmann et al. 2009, p. 420.
  18. ^ De Pascale et al. 2021, p. 9.
  19. ^ a b c d e f g Naranjo S., Moreno R. & Banks 1993, p. 9.
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Sources

Bibliography

External links

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