Submarine eruptions are

volcano A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most oft ...

eruptions which take place beneath the surface of water. These occur at constructive margins,

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

zones, and within

tectonic plates Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

due to hotspots. This eruption style is far more prevalent than subaerial activity. For example, it is believed that 70 to 80% of the Earth's magma output takes place at mid-ocean ridges.Parfitt, L. and Wilson, L. (2008) ''Fundamentals of Physical Volcanology'', Blackwell Publishing.

Detection

Fukutoku-Okanoba Eruption 08-12-2022 2127Z to 08-13-2022 0335Z

Submarine eruptions are less studied than subaerial

volcanoes A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

due to their inaccessibility. Developments in technology mean that submarine volcanoes can now be studied in greater detail. Despite this progress, understanding is still limited. Mid ocean ridges for example are the most active volcanic systems on Earth but roughly only 5% of their length has been studied in detail.Fagents, S.A., Gregg, T.K.P. and Lopes, R.M.C. (2013) ''Modelling Volcanic processes: the Physics and Mathematics of Volcanism'', Cambridge University Press, UK. Initial knowledge of these eruptions came from volcanic rocks being recovered from the ocean floor when repairs were made to the Transatlantic telegraph cable in the 1800s.Rubin, K.H., Soule, S.A., Chadwick, W.W., Farnan. D.J., Clague, A.A., Emberley. R.W., Baker, E.T., Perfit, M.R., Caress, D.W. and Dziak, R.P. (2012) Volcanic eruptions in the deep sea, ''Oceanography'', 25(1): 142-157. More recently a variety of techniques have been used to study these eruptions with significant developments being made since 1990. These include the use of remote controlled submersibles which can conduct surveys of the ocean floor. The use of hydrophone networks allows volcanic eruptions to be detected.
NOAA (2013) ''Recent Submarine Volcanic Eruptions''. Submersibles can be sent out in response to this to record the result of the eruption. Other tools have included seismic signals, acoustic waves and high resolution UAV multibeam mapping. Increasingly, eruptions at greater depths can be observed. For example, an explosive eruption at West Mata in Lau Basin at a depth of 1200 m was studied using submersibles.
Livescience (2011) ''Explosive Underwater Eruptions Are Deepest Yet Seen''

Controls on eruptive style

There is much variation in the style of submarine eruptions. This changes with a number of variables including magma

viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...

, water depth, effusion rate and volatile content. Many studies highlight the effects of

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

which increases with depth. It is believed that increased pressure restricts the release of volatile gases, resulting in effusive eruptions.Fransis, P. (1993) ''Volcanoes: A Planetary Perspective'', Oxford University Press. This is not to say that explosive eruptions do not occur at depth, just that a higher volatile content is required. It has been estimated that at 500 m explosive activity associated with basalts is suppressed, while depths greater than 2300 m would be sufficient to prevent the majority of explosive activity from

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

Shallow water eruptions

At shallow depths it is common for submarine eruptions to be explosive due to the reaction between volatiles in the magma and water which generates a significant quantity of steam.Head, J.W. and Wilson, L. (2008) Deep submarine pyroclastic eruptions: theory and predicted landforms and deposits, ''Journal of Volcanology and Geothermal Research'', 121: 155-193. These eruptions described as Surtseyan are characterised by large quantities of steam and gas and creating large amounts of

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of extremely vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicula ...

.
Smithsonian Institution National Museum of Natural History Global Volcanism Program (2013). This activity has occurred in many locations. An example is Fukuto-Okanoba near

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

. This activity has been observed for almost a century and causes discoloured water, jets of steam and ash, and pumice is found floating in the surrounding water.
Volcano Discovery (2013) Fukutoku-Okanoba volcano. Shallow eruptions can lead to the creation of islands. The most well known is Surtsey in

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

(1963-1967).Siebert, L., Simkin, T. and Kimberley, P. (2010) ''Volcanoes of the World'', University of California Press. Similar island building activity occurs frequently but these are often short lived. Volatile content is also significant. Magma being transported into the ocean through tunnels may see gases being exsolved before reaching the water and so the eruption is effusive. This has been seen in

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

Deep water eruption

With increased depth there is greater pressure and it is believed that this results in effusive eruptions.Decker, R. and Decker, B. (1989) ''Volcanoes'', W.H. Freeman and Company, USA. There is a variety of evidence, however, which suggests that explosive, pyroclastic activity can occur at depth. This includes observations of Pele's hair and evidence of

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

collapse.Wright, I.C. and Gamble, J.A. (1999) Southern Kermadec Submarine caldera arc volcanoes (South West Pacific): caldera formation by effusive and pyroclastic eruption, Marine Geology, 161:207-277 This activity is thought to be common at subduction zones due to recycling of the

lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...

. It is not exclusive to these plate margins, occurring at hotspots and ocean ridges. An example is Kamaʻehuakanaloa (formerly Loihi) near Hawaii where both effusive and explosive activity occurs at 2000 m depth. Two formations associated with submarine eruptions are seamounts and pillow lavas. Pillow lavas are created due to rapid cooling of lava which forms a skin. As more magma is forced into this the skin expands creating a lobe. When this fractures then lava seeps through the gap exposing hot lava to the water and again a skin forms over this: this process is then repeated.

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