Hudson volcano

stratovolcano 1905 m / 6,250 ft
Argentinien/Chile (Süden), Südamerika, -45.9°S / -72.97°W
Current status: normal or dormant (1 out of 5)
Last update: 25 Dec 2020 (Volcanic Alert Level raised to Yellow; increased seismic activity)
The ice-filled summit caldera of Cerro Hudson volcano
The ice-filled summit caldera of Cerro Hudson volcano

Cerro Hudson volcano in southern Chile is the southernmost active volcano of the Chilean Southern Volcanic Zone caused by subduction of the Nazca plate beneath the South American plate.
The massive Hudson volcano contains a 10 km wide, almost circular ice-filled caldera, which drains into the Huemules glacier to the north. Mudflows have been generated from this glacier down into the Río de Los Huemeles.
2 cinder cones are located north of the volcano. Other flank cones are found on the SW and SE flanks.
The remote volcano was not recognized as such until its first 20th-century eruption in 1971. An eruption in 1991 was Chile's second largest of the 20th century. It formed a new 800-m-wide crater in the SW part of the caldera.

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Typical eruption style: explosive
Hudson volcano eruptions: 2011, 1991, 1971, 1891
radiocarbon dated: 1740 ± 150, 860 AD ± 100, 390 AD ± 150, 120 BC ± 200, 790 BC ± 75, 1890 BC (?), 2250 BC, 3890 BC ± 500, 4750 BC (?), 4960 BC ± 150, 8010 BC (?)

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Background

Eruptions of Hudson volcano:
Hudson has been the source of several major Holocene explosive eruptions. At least 12 major explosive eruptions within the past 10,000 years have been identified by tephra layers.
An eruption about 6700 years ago must have been one of the largest known in the southern Andes during the past 10,000 years. Another eruption about 3600 years ago produced more than 10 cubic km of tephra.

Tectonic setting:
Hudson volcano still belongs to the Southern Volcanic Zone, related to the subduction of the Nazca Plate, but it is close to the triple junction of the Nazca-Antarctica-South American tectonic plates and located immediately north of the 300 km long Patagonian Volcanic Gap (46–49°S), where no recent volcanism has occured during the past 8 million years, as a result of the complex subduction of the Chile Rise spreading zone under South America at the Taitao Peninsula.

Sources:
- Smithsonian / GVP Hudson volcano information
- Charles R. Stern (2004) "Active Andean volcanism: its geologic and tectonic setting", Revista geológica de Chile, Vol. 31, No. 2, pp. 161-206

2007 earthquake
On 21 April, 2007, a magnitude 6.2 earthquake occurred at about 13:50 local time in the Aisén Fjord 50 km north of Hudson volcano. The earthquake is suspected to have triggered the eruption of Chaiten volcano 250 km north of the earthquake epicenter in May 2008.

1991 eruption of Hudson volcano
One of the largest eruption in Chile in the 20th century began from Hudson volcano on 8 August 1991 at 18:20 hr local time.
Phreatomagmatic explosions from a vent in the NW part of the caldera melted a 400 m wide hole in the glacier, and a magmatic phase of lava emission (fountains under the ice) lasted 4 days. Lava flows were erupted from a 4 km long NNE-SSW trending fissure.
The paroxysmal phase of the eruption began on 12 August around noon, producing a Plinian eruption column and forming an 800-m-wide crater 4 km SSE of the first crater. 3-4 hours after the main explosion, a jökullhaup (glacial flood) flowed down the Huemules valley to the coast. The eruption column reached an altitude of 17-18 km on 13 August, and ash fell as far as on the Falkland Islands (Malvinas Islands) 1000 km SE. The ash fall covered 100,000 sq km of southern Patagonia, and more than 1 cubic km of ash fell in Argentina alone.
On 20 August, Australian Airlines flight FL418 (Airbus) en route from Melbourne to Sydney encountered the ash plume in flight. The plume was dilute enough not to cause severe damage, but a strong smell of sulfurous gas entered the aircraft cabin and and was noticed by the crew and passengers.

Effects of the region
The most severe agricultural impacts were recorded in the Los Antiguos Valley 100 km SE of the volcano. Ashfall damaged houses, roads, and water supplies at Los Antiguos village. Its average 250-ton annual crop of cherries was destroyed by the eruption. Snowfall was greater than normal, with the total precipitation of 410 mm, compared to the average of 218 mm. In some areas, 30-40 % of sheep herds were killed, because the sheep were eating ash-covered grass and sometimes because of the the weight of ash of the back of some animals prevented them from standing up. Hndreds of sheep farms were abandoned in the Santa Cruz province of Argentina. There was a fast recovery of orchid crops after 2 years.

Causes of the eruption
The eruption of Hudson volcano was possibly triggered by a mixing of 2 magmas, a hot basaltic magma, which was erupted during the first phase, had been injected into a cooling chamber of trachyandesite magma stored at a depth of 2-3 km. The mixing caused an increase in volume and partial gas pressure and may have triggered the paroxysmal eruption at Hudson on 12 August 1991.

Sources:
- Smithsonian / GVP monthly reports
- Inbar et al (1995) "Environmental assessment of 1991 Hudson volcano eruption ashfall effects on southern Patagonia region, Argentina", Environmental Geology, Volume 25, Number 2, 119-125
- Kratzmann et al (2009) "Compositional variations and magma mixing in the 1991 eruptions of Hudson volcano, Chile", Bull. Volc., Volume 71, Number 4, pp 419-439

See also: Sentinel hub | Landsat 8
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