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
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]
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]
^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.
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^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.
S2CID131008771.
^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.
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1995GSAB..107.1398R.
doi:
10.1130/0016-7606(1995)107<1398:PVASDO>2.3.CO;2.
^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.
^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.
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^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.
Holt, S.J.; McPhie, J.; Carey, R.J. (November 2021). "Apparently 'dry' littoral rootless cones in Hawaiʻi formed by sustained, "confined" mixing of lava and sea water". Journal of Volcanology and Geothermal Research. 419: 107352.
Bibcode:
2021JVGR..41907352H.
doi:
10.1016/j.jvolgeores.2021.107352.
Jurado-Chichay, Zinzuni; Rowland, Scott K.; Walker, George P. L. (April 1996). "The formation of circular littoral cones from tube-fed p?hoehoe: Mauna Loa, Hawai'i". Bulletin of Volcanology. 57 (7): 471–482.
Bibcode:
1996BVol...57..471J.
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10.1007/BF00304433.
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