Littoral cone

A littoral cone lies on the right, on top of the cliffs

Littoral cones are a form of volcanic cone. They form from the interaction between lava flows and water. Steam explosions fragment the lava and the fragments can pile up and form a cone. Such cones usually form on ʻaʻā lava flows, and typically are formed only by large lava flows. They have been found on Hawaii and elsewhere.

Description[edit]

Littoral cones are semicircular cones which are breached in the direction of the lava flow that created them. They are formed by mounds of clasts that appear like cones without a crater.[1] Littoral cones are constructed by volcanic ash, lava bombs and lapilli.[2] Their component material is usually poorly sorted and can feature agglutinated structures and layering.[3] Sometimes spatter-fed lava flows occur on such cones.[4] They are formed by degassed hyaloclastite.[5][1] The most common form found on Hawaiʻi involves two semicircles on both sides of the lava flow that generated them;[6] some such cones in Hawaiʻi form a complete rim with diameters of 200–400 metres (660–1,310 ft).[7] Puʻu Kī in Hawaiʻi has nested craters on top of a lava tube.[8] Typically such cones are not larger than 800 metres (2,600 ft) wide and 75 metres (246 ft) high.[3] Other smaller cones in Hawaii have diameters of 40 metres (130 ft) and heights reaching 15 metres (49 ft).[9] They are not as well known as the Icelandic pseudocraters.[10]

Littoral cones not primary volcanic vents and distinguishing between a littoral cone and a primary vent can be difficult.[3] A littoral cone forms when lava flows from land into water. Interaction between the water and the lava leads to steam explosions. These explosions throw lava fragments into the air; under favourable circumstances these fragments pile up on land and form a cone.[11] This activity may resemble that of fire fountaining,[9] and produces tephra columns, lava bubbles, steam blasts and lava fountains.[12] Repeated phases of magma-water mixing lead to the formation of bedded deposits.[2] The steam explosions can lead to the formation of Pele's hair.[13] There are two types of such cones, depending on whether the magma-water mixing was free or whether it occurred in an enclosed environment; the former produces typical phreatomagmatic deposits, the latter more ash-poor cones than the former.[10]

The forming lava flows need to be sufficiently large;[14] the minimum size of lava flows that have formed such cones in Hawaiʻi is 38,000,000 cubic metres (50,000,000 cu yd).[15] Of these, about 5-6% of their volume is converted to fragments.[3] Usually littoral cones are formed by ʻaʻā lava as their fragmented nature allows ideal water-lava interactions, but pāhoehoe and intermediary lavas can also form littoral cones.[16] Other properties such as the speed of the lava flow and the structure of the flow front also influence the formation of littoral cones.[15] Larger lava flow rates generate larger cones.[17] In some littoral cones in Hawaiʻi that were formed by pāhoehoe lava flows, the collapse of a lava bench and subsequent steam explosions formed the cones instead.[7] Pyroclastic flows can also form littoral cones, one such cone has been found on Lombok and formed during the 1257 Samalas eruption.[18]

Examples[edit]

Pseudocraters and littoral cones have been found on Iceland, Hawaiʻi, Cerro Azul in the Galápagos Islands,[7] Deception Island, Antarctica,[19] and Medicine Lake Volcano, California.[20] Sometimes the words "pseudocrater" and "littoral cone" are used as synonyms.[21] Littoral cones are usually quickly removed by sea erosion; thus littoral cones rarely survive as landscape features.[11]

Prehistorical littoral cones have been found on the coast of Hawaiʻi, where the volcanoes Mauna Loa and Kīlauea face the sea. They were named "littoral cones" by Wentworth in 1938.[22] About 50 large cones are found on these two volcanoes and only three of them were formed during historical times; no such cones have been found on the other Hawaiian volcanoes.[11] The Puʻu ʻŌʻō and Mauna Ulu eruptions of Kīlauea have also formed small littoral cones.[7]

Examples of littoral cones include Sand Hills (1840 eruption) on Kīlauea in Hawaiʻi,[23] ʻAuʻau, Nā Puʻu a Pele, Puʻu Hou (1868 eruption) and Puʻu Kī (eruption 1300 years ago) at Mauna Loa in Hawaiʻi,[6] a cone close to Villamil at Sierra Negra, Galapagos,[24] several cones south of Krýsuvík[25] and Eldborg (1800 years ago) at Hengill both on Iceland,[26] a cone in the Winter Water unit of the Columbia Plateau Basalts, Oregon,[27] several cones along the shores of Lake Kivu in East Africa,[28] a cone at Becharof Lake, Alaska,[29] Burilan and Devil Rock on Gaua,[30] and Ponta de Ferraria (eruption 840 ± 60 years ago) on São Miguel Island, Azores.[31] The Speedwell Vent in Derbyshire, United Kingdom may also be a littoral cone of Carboniferous age.[32] Pleistocene littoral cones may also exist in Lake Tahoe, California,[33] while Archean littoral cones may have formed in the Barberton Greenstone Belt of South Africa.[34]

References[edit]

  1. ^ a b Fisher 1968, p. 839.
  2. ^ a b Richard V. Fisher; Hans-Ulrich Schmincke (6 December 2012). Pyroclastic Rocks. Springer Science & Business Media. pp. 263–264. ISBN 978-3-642-74864-6.
  3. ^ a b c d Green, Jack (1982-01-01). "Littoral cones". Beaches and Coastal Geology. Encyclopedia of Earth Science. Springer US. pp. 519–520. doi:10.1007/0-387-30843-1_260. ISBN 9780879332136.
  4. ^ Greeley, Ronald; Fagents, Sarah A. (25 September 2001). "Icelandic pseudocraters as analogs to some volcanic cones on Mars". Journal of Geophysical Research: Planets. 106 (E9): 20533. Bibcode:2001JGR...10620527G. doi:10.1029/2000JE001378.
  5. ^ Jurado-Chichay, Rowland & Walker 1996, p. 477.
  6. ^ a b Jurado-Chichay, Rowland & Walker 1996, p. 472.
  7. ^ a b c d Jurado-Chichay, Rowland & Walker 1996, p. 471.
  8. ^ Walker, George P. L. (1993). "Basaltic-volcano systems" (PDF). Geological Society, London, Special Publications. 76 (1): 25. Bibcode:1993GSLSP..76....3W. doi:10.1144/GSL.SP.1993.076.01.01. S2CID 128692790.
  9. ^ a b Jurado-Chichay, Rowland & Walker 1996, p. 478.
  10. ^ a b Holt, McPhie & Carey 2021, p. 2.
  11. ^ a b c Moore & Ault 1965, p. 3.
  12. ^ Holt, McPhie & Carey 2021, p. 3.
  13. ^ Mattox, Tari N; Mangan, Margaret T (January 1997). "Littoral hydrovolcanic explosions: a case study of lava–seawater interaction at Kilauea Volcano". Journal of Volcanology and Geothermal Research. 75 (1–2): 6–8. Bibcode:1997JVGR...75....1M. doi:10.1016/S0377-0273(96)00048-0.
  14. ^ Moore & Ault 1965, p. 9.
  15. ^ a b Moore & Ault 1965, p. 10.
  16. ^ Fisher 1968, p. 861.
  17. ^ Jurado-Chichay, Rowland & Walker 1996, p. 481.
  18. ^ Vidal, Céline M.; Komorowski, Jean-Christophe; Métrich, Nicole; Pratomo, Indyo; Kartadinata, Nugraha; Prambada, Oktory; Michel, Agnès; Carazzo, Guillaume; Lavigne, Franck; Rodysill, Jessica; Fontijn, Karen; Surono (8 August 2015). "Dynamics of the major plinian eruption of Samalas in 1257 A.D. (Lombok, Indonesia)". Bulletin of Volcanology. 77 (9): 7. Bibcode:2015BVol...77...73V. doi:10.1007/s00445-015-0960-9. S2CID 127929333.
  19. ^ Smellie, J.L. (27 April 2004). "Lithostratigraphy and volcanic evolution of Deception Island, South Shetland Islands". Antarctic Science. 13 (2): 201. doi:10.1017/S0954102001000281. S2CID 131008771.
  20. ^ "DIGITAL GEOLOGIC MAP DATABASE OF MEDICINE LAKE VOLCANO, CALIFORNIA". gsa.confex.com. Retrieved 2016-11-24.
  21. ^ EINARSSON, ARNI (February 1982). "The palaeolimnology of Lake Myvatn, northern Iceland: plant and animal microfossils in the sediment". Freshwater Biology. 12 (1): 65. Bibcode:1982FrBio..12...63E. doi:10.1111/j.1365-2427.1982.tb00603.x.
  22. ^ Fisher 1968, p. 842.
  23. ^ Fisher 1968, p. 841.
  24. ^ Reynolds, Robert W.; Geist, Dennis; Kurz, Mark D. (December 1995). "Physical volcanology and structural development of Sierra Negra volcano, Isabela Island, Gal´apagos archipelago". Geological Society of America Bulletin. 107 (12): 1401–1402. Bibcode:1995GSAB..107.1398R. doi:10.1130/0016-7606(1995)107<1398:PVASDO>2.3.CO;2.
  25. ^ Hersir, Gylfi Páll; Árnason, Knútur; Vilhjálmsson, Arnar Már; Saemundsson, Kristján; Ágústsdóttir, Þorbjörg; Friðleifsson, Guðmundur Ómar (27 November 2018). "Krýsuvík high temperature geothermal area in SW Iceland: Geological setting and 3D inversion of magnetotelluric (MT) resistivity data". Journal of Volcanology and Geothermal Research. 391: 6. doi:10.1016/j.jvolgeores.2018.11.021. ISSN 0377-0273. S2CID 135282804.
  26. ^ Stevenson, J. A.; Mitchell, N.; Mochrie, F.; Cassidy, M.; Pinkerton, H. (2009-12-01). "Lava entering water: the different behaviour of aa and pahoehoe at the Nesjahraun, Thingvellir, Iceland". AGU Fall Meeting Abstracts. 51: V51D–1749. Bibcode:2009AGUFM.V51D1749S.
  27. ^ "COLUMBIA RIVER BASALT AQUIFER CHARACTERISTICS REVEALED BY STATEMAP MAPPING IN OREGON'S UMATILLA BASIN". gsa.confex.com. Retrieved 2016-11-24.
  28. ^ Balagizi, Charles M.; Kies, Antoine; Kasereka, Marcellin M.; Tedesco, Dario; Yalire, Mathieu M.; McCausland, Wendy A. (1 August 2018). "Natural hazards in Goma and the surrounding villages, East African Rift System". Natural Hazards. 93 (1): 57. Bibcode:2018NatHa..93...31B. doi:10.1007/s11069-018-3288-x. ISSN 1573-0840. S2CID 134491982.
  29. ^ Lu, Zhong; Wicks, Charles; Dzurisin, Daniel; Power, John A.; Moran, Seth C.; Thatcher, Wayne (July 2002). "Magmatic inflation at a dormant stratovolcano: 1996-1998 activity at Mount Peulik volcano, Alaska, revealed by satellite radar interferometry". Journal of Geophysical Research: Solid Earth. 107 (B7): 4. Bibcode:2002JGRB..107.2134L. doi:10.1029/2001JB000471.
  30. ^ Métrich, N.; Bertagnini, A.; Garaebiti, E.; Vergniolle, S.; Bani, P.; Beaumais, A.; Neuville, D.R. (August 2016). "Magma transfer and degassing budget: Application to the 2009–2010 eruptive crisis of Mt Garet (Vanuatu arc)". Journal of Volcanology and Geothermal Research. 322: 49. Bibcode:2016JVGR..322...48M. doi:10.1016/j.jvolgeores.2015.06.003.
  31. ^ Lima, Ana; Nunes, João Carlos; Brilha, José (9 November 2016). "Monitoring of the Visitors Impact at "Ponta da Ferraria e Pico das Camarinhas" Geosite (São Miguel Island, Azores UNESCO Global Geopark, Portugal)" (PDF). Geoheritage. 9 (4): 3. doi:10.1007/s12371-016-0203-2. hdl:1822/45592. S2CID 132477543.
  32. ^ Cheshire, S. G.; Bell, J.D. (1 December 1976). "The Speedwell Vent, Castleton, Derbyshire: A Carboniferous Littoral Cone". Proceedings of the Yorkshire Geological Society. 41 (2): 173–184. Bibcode:1976PYGS...41..173C. doi:10.1144/pygs.41.2.173.
  33. ^ "PLIOCENE/PLEISTOCENE BASALTIC PILLOW LAVA AND TUFF ALONG NW SHORE OF LAKE TAHOE, CA: NEARSHORE VENT OR LITTORAL CONE?". gsa.confex.com. Retrieved 2016-11-24.
  34. ^ Huber, M. S.; Byerly, G. R. (1 December 2018). "Volcanological and petrogenetic characteristics of komatiites of the 3.3 Ga Saw Mill Complex, Weltevreden Formation, Barberton Greenstone Belt, South Africa". South African Journal of Geology. 121 (4): 479. Bibcode:2018SAJG..121..463H. doi:10.25131/sajg.121.0031. ISSN 1012-0750. S2CID 56281060.

Sources[edit]

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