Freatska erupcija

Freatska erupcija, imenovana tudi freatska eksplozija, ultravulkanski izbruh ali parni izbruh,^[1] se pojavi, ko magma segreje podtalnico ali površinsko vodo. Ekstremna temperatura magme (od 500 do 1170 °C) povzroči skoraj takojšnje izhlapevanje vode v paro, kar ima za posledico eksplozijo pare, vode, pepela, kamenja in vulkanskih bomb. Na gori Sveta Helena v zvezni državi Washington je leta 1980 pred plinijskim izbruhom vulkana leta 1980 prišlo na stotine parnih eksplozij.^[2] Manj intenziven geotermalni dogodek lahko povzroči blatni vulkan.

Freatski izbruhi običajno vključujejo paro in kamenine; vključitev tekoče lave je nenavadna. Temperatura drobcev se lahko giblje od mrzle do žareče. Če je vključena staljena magma, vulkanologi dogodek razvrstijo kot freatomagmatski izbruh. Ti izbruhi občasno ustvarijo široke kraterje z nizkim reliefom, imenovane maari. Freatske eksplozije lahko spremljajo emisije ogljikovega dioksida ali vodikovega sulfida. Ogljikov dioksid lahko pri zadostni koncentraciji povzroči zadušitev; vodikov sulfid deluje kot strup širokega spektra. Freatski izbruh leta 1979 na otoku Java je ubil 140 ljudi, večino so premagali strupeni plini.^[3]

Maar in njihov nastanek

Freatske eksplozije so odgovorne za nastanek številnih maarov, v katerih je bil izvržen le star material. Maar je širok plitev vulkanski krater z nizkim reliefom, ki ga povzroči freatomagmatska erupcija. Maar se pogosto napolni z vodo in tvori relativno plitko kratersko jezero. Večina obročastih sten na dnu podložena z brečami starih kamnin, ki so bile odstranjene ob čiščenju dimnika. Kažejo, da so tem magmatskim izbruhom sledili freatski izbruhi. Nekateri avtorji zato to zaporedje od freatskih do magmatskih izbruhov imenujejo freatomagmatski izbruhi.

Primeri freatske erupcije

Cumbre Vieja – ob izbruhu leta 2021 na otoku La Palma (Kanarski otoki) so se novi eruptivni zračniki po navadi napovedali s freatsko eksplozijo, ki ji je kmalu zatem sledilo odprtje novega zračnika v razpokah na istem mestu.
Krakatav – Indonezija, 1883 – domneva se, da je bil izbruh, ki je izbrisal večino vulkanskega otoka in ustvaril najglasnejši zvok v zgodovini, freatomagmatski dogodek.^[4]^[5]
Otok Ritter – Papuanska Nova Gvineja, 1888 (glej Izbruh in cunami na otoku Ritter leta 1888) – povzročilo največje bočno širjenje vulkanskega stožca v človeški zgodovini.^[6]
Kilauea – Havaji, Združene države Amerike – vulkan ima dolgo zgodovino freatskih eksplozij; freatski izbruh leta 1924 je vrgel skale, ocenjene na osem ton, na razdaljo enega kilometra.^[7]
Surtsey – Islandija, 1963–65
Vulkan Taal – Filipini, 1965, 1977, 2020
Ontake – Japonska, 2014 (glej izbruh Ontake 2014)
Vulkan Mayon – Filipini, 2013
Whakaari/Beli otok]] – Nova Zelandija, 2019 (glej izbruh Whakaari/White Island 2019)
Bulusan – Filipini, 2022 je stratovulkan na otoku Luzon.

Sklici

↑ Mullineaux, D.R. et al. (1987) Volcanic Hazards in the Hawaiian Islands in Volcanism in Hawaii, volume 1, USGS Professional Paper 1350, page 602.
↑ »VHP Photo Glossary: Phreatic eruption«. Volcano Hazards Program. U.S. Geological Survey. Pridobljeno 13. novembra 2010.
↑ "On February 20th, 1979, 142 inhabitants of Dieng Plateau (Indonesia) were asphyxiated by poisonous gases during a mild phreatic eruption. From later fields gas collection and analysis, the casualties are considered to be due to CO2 rich volcanic gases." F. Le Guern, H. Tazieff and R. Faivre Pierret, "An example of health hazard: People killed by gas during a phreatic eruption: Diëng plateau (Java, Indonesia), February 20th 1979", Bulletin of Volcanology 45 (1982): 153–156.
↑ "A precursory phreatic or phreatomagmatic stage has been identified in the 1883 Krakatau eruption (Simkin and Fiske, 1983)". A precursory phreatic or phreatomagmatic stage has been identified in the 1883 Krakatau eruption (Simkin and Fiske, 1983). David J. W. Piper, Georgia Pe-Piper and Darren Lefort, "Precursory activity of the 161 ka Kos Plateau Tuff eruption, Aegean Sea (Greece)", Bulletin of Volcanology 72 (2010): 657–669.
↑ Simkin T, Fiske RS (1983) Krakatau 1883: The Volcanic Eruption and its Effects. Smithsonian Institution Press, Washington.
↑ Steven N. Ward and Simon Day (2003). »Ritter Island Volcano—lateral collapse and the tsunami of 1888«. Geophysical Journal International. 154 (3): 891–902. Bibcode:2003GeoJI.154..891W. doi:10.1046/j.1365-246X.2003.02016.x.
↑ "On May 10, 1924, a violent phreatic (steam) eruption began in Halema'uma'u that sent repeated columns of ash high into the sky. The explosions continued for 18 days, with the largest occurring on May 18. The steam explosions hurled rocks as large as eight tons as far as 0.6 miles from the crater; these blocks still surround Halema'uma'u. One of these blocks fatally injured a Mr. Taylor, who approached too close to the crater to take a photograph." Phreatic Eruptions, Hawaiian Volcano Observatory, US Geological Survey, 6 May 1994.

Zunanje povezave

Wikimedijina zbirka ponuja več predstavnostnega gradiva o temi: Freatska erupcija.

[1] Mullineaux, D.R. et al. (1987) Volcanic Hazards in the Hawaiian Islands in Volcanism in Hawaii, volume 1, USGS Professional Paper 1350, page 602.

[USGS-2] »VHP Photo Glossary: Phreatic eruption«. Volcano Hazards Program. U.S. Geological Survey. Pridobljeno 13. novembra 2010.

[3] "On February 20th, 1979, 142 inhabitants of Dieng Plateau (Indonesia) were asphyxiated by poisonous gases during a mild phreatic eruption. From later fields gas collection and analysis, the casualties are considered to be due to CO2 rich volcanic gases." F. Le Guern, H. Tazieff and R. Faivre Pierret, "An example of health hazard: People killed by gas during a phreatic eruption: Diëng plateau (Java, Indonesia), February 20th 1979", Bulletin of Volcanology 45 (1982): 153–156.

[4] "A precursory phreatic or phreatomagmatic stage has been identified in the 1883 Krakatau eruption (Simkin and Fiske, 1983)". A precursory phreatic or phreatomagmatic stage has been identified in the 1883 Krakatau eruption (Simkin and Fiske, 1983). David J. W. Piper, Georgia Pe-Piper and Darren Lefort, "Precursory activity of the 161 ka Kos Plateau Tuff eruption, Aegean Sea (Greece)", Bulletin of Volcanology 72 (2010): 657–669.

[5] Simkin T, Fiske RS (1983) Krakatau 1883: The Volcanic Eruption and its Effects. Smithsonian Institution Press, Washington.

[6] Steven N. Ward and Simon Day (2003). »Ritter Island Volcano—lateral collapse and the tsunami of 1888«. Geophysical Journal International. 154 (3): 891–902. Bibcode:2003GeoJI.154..891W. doi:10.1046/j.1365-246X.2003.02016.x.

[7] "On May 10, 1924, a violent phreatic (steam) eruption began in Halema'uma'u that sent repeated columns of ash high into the sky. The explosions continued for 18 days, with the largest occurring on May 18. The steam explosions hurled rocks as large as eight tons as far as 0.6 miles from the crater; these blocks still surround Halema'uma'u. One of these blocks fatally injured a Mr. Taylor, who approached too close to the crater to take a photograph." Phreatic Eruptions, Hawaiian Volcano Observatory, US Geological Survey, 6 May 1994.

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