Ora Caldera

Ora Caldera
Ora Caldera
Highest point
Elevation234 m (768 ft)
Coordinates46°20′49″N 11°17′51″E / 46.34687°N 11.29747°E / 46.34687; 11.29747
Dimensions
Length40 km (25 mi)
Width42 km (26 mi)
Area1,680 km2 (650 mi2)[1]
Geography
CountryItaly
Geology
Formed byTrans-tensional
OrogenyAlps
Rock age274 Ma
Mountain typeCaldera
Rock typeRhyolite
Volcanic beltAthesian Volcanic Group
Last eruption274 Ma

The Ora Caldera is an extinct Permian supervolcano in the Southern Alps of northern Italy.[2] This 42-kilometre-wide (26 mi) and 40-kilometre-long (25 mi) caldera was formed by a supereruption 277–274 million years ago that produced more than 1,300 km3 (310 mi3) of rhyodacitic-rhyolitic ignimbrite.[2][3][4] The ignimbrite from this eruption forms the 10-to-1,350-metre-thick (33 to 4,429 ft) Ora Formation, which represents the youngest eruptive unit of the Athesian Volcanic Group.[2][4]

Geology

Even though Ora erupted between 277 and 274 Ma (also known as The Permian Ora Formation), the preservation of erupted rhyolite is exceptionally good. This is because the southern Alps region has been remarkably stable. This means erosion exposed the Ora formation is largely undeformed and unmetamorphosed, with sub-horizontal dips and essentially no post-emplacement disruption.[5]

Eruption

The eruptions of the Ora Formation between 277-274 Ma were characterized by crystal-rich (~25 to 55%) and ubiquitously welded. This means the eruption was highly explosive and high volume ignimbrite.[2]

Ora is the youngest eruption of the larger Athesian Volcanic Group (AVG) during the Carboniferous. Volcanism here is tied to the closing of the Paleo-Tethys Ocean, large scale extensional and strike-slip tectonics, and the collapse of the Variscan Orogenic Belt.[2] This belt covers over 2,000 square kilometres (770 mi2) in northern Italy. Pre eruption strata includes two unconformities'. The lowest is made up of a Variscan South-Alpine metamorphic basement, while the upper layer is continental red beds (Val Gardena Sandstone).[6]

Evidence shows the eruption started in the south portion of the caldera and progressed to the north, forming the two different caldera depressions. There is also evidence of multiple magma chambers in the Ora system.[7] This also might show that there were multiple vents erupting at once, incremental caldera filling of subtly compositionally different pyroclastic flow pulses, and an eruption of lower intensity.[7]

Volcanic rock characteristics

The Andriano Formation is one of the best and most well preserved formations in the Ora complex. It is a massive, rhyolitic lava of red-orange to brick red or red-purple color, with diffuse flow bands of variable thickness (5 to 20 cm). The shape of flow bands range from flat-parallel or slightly wavy to strongly wavy and some flow bands even intersect each other with variable angles.[6]

Volcanic rocks show a porphyric structure with idiomorphic phenocrysts (1-4 mm) of feldspar and quartz that appears to have completely recrystallized under a microscope. It is also crystal-rich, poorly sorted, and has common fiamme and pumice.[6][2]

Eruption Comparison

See also: Volcanic explosivity index

Below is a comparison of the Ora Caldera eruption to other explosive volcanic eruptions:

Name Location VEI Rock Type Eruptive Volume (km3) Eruption Date Ref
Ora caldera Italy 8 Rhyolite 1290 ~277-274 Ma [7]
Cottonwood Wash Tuff Utah (United States) 8 Dacite 2000 31.1 Ma [7]
Wah Wah Springs Caldera Utah (United States) 8 Dacite 5900 30 Ma [8]
Lake Toba Indonesia 8 Rhyolite 2800 ~74,000 [9][10]
Yellowstone (Huckleberry ridge) Wyoming (United States) 8 Rhyolite 2450 ~2.1 Ma [11]
La Garita Colorado (United States) 8 Dacite 3000+ ~27.8 Ma [12]
Mount Tambora Indonesia 7 Trachyandesite 130 1815 AD [13]
Lund Caldera Utah 8 Dacite 4400 29 Ma [7]
Yellowstone (Lava Creek) Wyoming (United States) 8 Rhyolite 1000 630,000 BC [14]
Long Valley Caldera (Bishop Tuff) California (United States) 7 Rhyolite 650 ~764,800 ± 600 [15]
Krakatoa Indonesia 6 Dacite to Rhyodacite 18-21 1883 AD [16]
Mount Vesuvius Italy 5 Tephra, Phonolite 6.4 79 AD [17]
Mount Saint Helens Washington (United States) 5 Dacite 2.5 1980 AD [18]
Lake Taupō New Zealand 8 Rhyolite 1100 25,500 BC [19]
Mount Pinatubo Philippines 6 Dacite 10 1991 AD [20]
Santorini Greece 6-7 Dacite 78-86 1610 BC [21]
Novarupta Alaska (United States) 6 Rhyolite 17 1912 AD [22]
Mount Mazama Oregon (United States) 7 Dacite 176 7700 BC [7]
Valles Caldera (Bandelier Tuff) New Mexico (United States) 7 Rhyolite 300 1.2 Ma [7]
Campi Flegrei Italy 6 Trachyte, Trachydacite 40 12,800 BC [23]

See also

References

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  2. ^ a b c d e f Willcock, M.A.W.; Cas, R.A.F.; Giordano, G.; Morelli, C. (2013). "The eruption, pyroclastic flow behaviour, and caldera in-filling processes of the extremely large volume (> 1290 km3), intra- to extra-caldera, Permian Ora (Ignimbrite) Formation, Southern Alps, Italy". Journal of Volcanology and Geothermal Research. 265: 102–126. Bibcode:2013JVGR..265..102W. doi:10.1016/j.jvolgeores.2013.08.012. Retrieved 2022-06-29.
  3. ^ "The eruption, pyroclastic flow behaviour, and caldera infilling processes of the large volume (>1000 km3), Permian Ora (Ignimbrite) Formation (Italy)". Retrieved 2022-06-29.
  4. ^ a b "Ora Caldera". Retrieved 2022-06-29.
  5. ^ Willcock, M.A.W.; Cas, R.A.F.; Giordano, G.; Morelli, C. (September 2013). "The eruption, pyroclastic flow behaviour, and caldera in-filling processes of the extremely large volume (>1290km3), intra- to extra-caldera, Permian Ora (Ignimbrite) Formation, Southern Alps, Italy". Journal of Volcanology and Geothermal Research. 265: 102–126. Bibcode:2013JVGR..265..102W. doi:10.1016/j.jvolgeores.2013.08.012. Retrieved 3 January 2026.
  6. ^ a b c Brandner, Rainer; Gruber, Alfred; Morelli, Corrado; Mair, Volkmar (September 2016). Pulses of Neotethys-Rifting in the Permomesozoic of the Dolomites. p. 7-70. Retrieved 3 January 2026.
  7. ^ a b c d e f g Willcock, M.A.W.; Bargossi, G.M.; Weinberg, R.F.; Gasparotto, G.; Cas, R.A.F.; Giordano, G.; Marocchi, M. (November 2015). "A complex magma reservoir system for a large volume intra- to extra-caldera ignimbrite: Mineralogical and chemical architecture of the VEI8, Permian Ora ignimbrite (Italy)". Journal of Volcanology and Geothermal Research. 306: 17–40. Bibcode:2015JVGR..306...17W. doi:10.1016/J.JVOLGEORES.2015.09.015. Retrieved 3 January 2026.
  8. ^ Best, Myron G.; Christiansen, Eric H.; Deino, Alan L.; Gromme, Sherman; Hart, Garret L.; Tingey, David G. (August 2013). "The 36–18 Ma Indian Peak–Caliente ignimbrite field and calderas, southeastern Great Basin, USA: Multicyclic super-eruptions". Geosphere. 9 (4): 864–950. Bibcode:2013Geosp...9..864B. doi:10.1130/GES00902.1. Retrieved 3 January 2026.
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  10. ^ "Volcano Watch — Supersized eruptions are all the rage! | U.S. Geological Survey". www.usgs.gov. Hawaii Volcano Observatory. 28 April 2005. Retrieved 3 January 2026.
  11. ^ Swallow, Elliot J; Wilson, Colin J N; Charlier, Bruce L A; Gamble, John A (1 July 2019). "The Huckleberry Ridge Tuff, Yellowstone: evacuation of multiple magmatic systems in a complex episodic eruption". Journal of Petrology. 60 (7): 1371–1426. doi:10.1093/petrology/egz034. Retrieved 3 January 2026.
  12. ^ "In the pantheon of caldera eruptions, where does Yellowstone rank? | U.S. Geological Survey". www.usgs.gov. Yellowstone Volcano Observatory. 26 December 2022. Retrieved 3 January 2026.
  13. ^ "This Day In History: Mount Tambora Explosively Erupts in 1815". National Environmental Satellite, Data, and Information Service. 22 December 2025. Retrieved 3 January 2026.
  14. ^ "Yellowstone U.S. Geological Survey". www.usgs.gov. Yellowstone National Park, Wyoming: Yellowstone Volcano Observatory. 22 December 2025. Retrieved 3 January 2026.
  15. ^ Hildreth, Wes; Fierstein, Judy; Calvert, Andrew T. (January 2023). "Precaldera Mafic Magmatism at Long Valley, California: Magma-Tectonic Siting and Incubation of the Great Rhyolite System". Journal of Volcanology and Geothermal Research. 433 107726. Bibcode:2023JVGR..43307726H. doi:10.1016/j.jvolgeores.2022.107726. Retrieved 3 January 2026.
  16. ^ Self, Stephen; Rampino, Michael R. (December 1981). "The 1883 eruption of Krakatau". Nature. 294 (5843): 699–704. Bibcode:1981Natur.294..699S. doi:10.1038/294699a0. Retrieved 3 January 2026.
  17. ^ Scarpati, Claudio; Chiominto, Giulia; Santangelo, Ileana; Perrotta, Annamaria; Fedele, Lorenzo (6 January 2025). "The ad 79 Vesuvius eruption revisited: Plinian and post-Plinian falls". Journal of the Geological Society. 182 (1) jgs2024-071. Bibcode:2025JGSoc.182...71S. doi:10.1144/jgs2024-071. Retrieved 3 January 2026.
  18. ^ "1980 Cataclysmic Eruption U.S. Geological Survey". www.usgs.gov. United States Geological Survey. 7 November 2023. Retrieved 3 January 2026.
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  20. ^ "Impacts & Mitigation - Pinatubo 1991". volcanoes.usgs.gov. United States Geological Survey. 8 March 2022. Retrieved 3 January 2026.
  21. ^ Bruins, Hendrik J.; Keller, Jörg; Klügel, Andreas; Kisch, Hanan J.; Katra, Itzhak; van der Plicht, Johannes (14 January 2019). "Tephra in caves: Distal deposits of the Minoan Santorini eruption and the Campanian super-eruption". Quaternary International. 499: 135–147. Bibcode:2019QuInt.499..135B. doi:10.1016/j.quaint.2018.09.040. Retrieved 3 January 2026.
  22. ^ Hildreth, Wes; Fierstein, Judy (10 May 2012). "The Novarupta-Katmai Eruption of 1912--Largest Eruption of the Twentieth Century: Centennial Perspectives". pubs.usgs.gov. United States Geological Survey. Retrieved 3 January 2026.
  23. ^ "Campi Flegrei, Italy - NASA Science". NASA. 8 January 2013. Retrieved 3 January 2026.
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