Submarine eruption

Submarine eruptions are those volcano eruptions which take place beneath the surface of water. These occur at constructive margins, subduction zones and within tectonic plates 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.[1]

Submarine Eruption-numbers
Scheme of a submarine eruption. 1 Water vapor cloud 2 Water 3 Stratum 4 Lava flow 5 Magma conduit 6 Magma chamber 7 Dike 8 Pillow lava

Detection

Submarine eruptions are less studied than subaerial volcanoes 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.[2]

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.[3] 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.[3] The use of hydrophone networks allows volcanic eruptions to be detected.[4] Submersibles can be sent out in response to this to record the result of the eruption.[4] Other tools have included seismic signals, acoustic waves and high resolution UAV multibeam mapping.[3]

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.[5]

Controls on eruptive style

There is much variation in the style of submarine eruptions.[3] This changes with a number of variables including magma viscosity, water depth, effusion rate and volatile content.[2] Many studies highlight the effects of pressure which increases with depth. It is believed that increased pressure restricts the release of volatile gases, resulting in effusive eruptions.[6] 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 lava.[1]

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.[7] These eruptions described as Surtseyan are characterised by large quantities of steam and gas and creating large amounts of pumice.[8] This activity has occurred in many locations. An example is Fukuto-Okanoba near Japan. 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.[9]

Shallow eruptions can lead to the creation of islands. The most well known is Surtsey in Iceland (1963-1967).[10] Similar island building activity occurs frequently but these are often short lived.[10]

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.

Deep water eruption

With increased depth there is greater pressure and it is believed that this results in effusive eruptions.[11] There is a variety of evidence, however, which suggests that explosive, pyroclastic activity can occur at depth. This includes observations of Pele's hair[12] and evidence of caldera collapse.[13] This activity is thought to be common at subduction zones due to recycling of the lithosphere.[3] It is not exclusive to these plate margins, occurring at hotspots and ocean ridges. An example is 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.[11] 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.[11]

See also

References

  1. ^ a b Parfitt, L. and Wilson, L. (2008) Fundamentals of Physical Volcanology, Blackwell Publishing.
  2. ^ a b 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.
  3. ^ a b c d e 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.
  4. ^ a b [1], NOAA (2013) Recent Submarine Volcanic Eruptions.
  5. ^ [2], Livescience (2011) Explosive Underwater Eruptions Are Deepest Yet Seen
  6. ^ Fransis, P. (1993) Volcanoes: A Planetary Perspective, Oxford University Press.
  7. ^ 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.
  8. ^ [3], Smithsonian Institution National Museum of Natural History Global Volcanism Program (2013).
  9. ^ [4], Volcano Discovery (2013) Fukutoku-Okanoba volcano.
  10. ^ a b Siebert, L., Simkin, T. and Kimberley, P. (2010) Volcanoes of the World, University of California Press.
  11. ^ a b c Decker, R. and Decker, B. (1989) Volcanoes, W.H. Freeman and Company, USA.
  12. ^ Cashman, K. V.; Sparks, R. S. J. (2013). "How volcanoes work: A 25 year perspective". Geological Society of America Bulletin. 125 (5–6): 664–690. doi:10.1130/B30720.1. ISSN 0016-7606.
  13. ^ 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

External links

1955 Hawaiian submarine eruption

The 1955 Hawaiian submarine eruption was a submarine eruption that occurred 90 km (56 mi) northeast of Necker Island on August 20, 1955. Steaming water, water discoloration and an eruption column took place during the eruption. A possible pumice raft was also witnessed. The eruption originated about 4 km (2.5 mi) below sea level from an unnamed submarine volcano. The eruption produced a column of smoke several meters high. It is probably the westernmost historical eruption within the Hawaiian Islands. Another but less certain submarine eruption may have occurred 60 km (37 mi) northwest of Oahu on May 22, 1956.

2011–12 El Hierro eruption

The 2011-2012 El Hierro eruption occurred just off the island of El Hierro, the smallest and farthest south and west of the Canary Islands (an Autonomous Community of Spain), in the Atlantic Ocean off the coast of Africa. The island is also the youngest in the volcanic chain. The October 2011 - March 2012 eruption was underwater, with a fissure of vents located approximately 2 km to the south of the fishing village of La Restinga on the southern coast of the island. As of June 2012, increased seismicity to the north-west of the vent suggests another phase in the area's volcanic activity - comprising just deep-seated magma movements with associated earthquakes and deformation of the island at this June 2012 stage - is under way. A second phase of eruptive activity has not yet occurred, and it does not necessarily follow that it will occur.

Axial Seamount

Axial Seamount (also Coaxial Seamount or Axial Volcano) is a seamount and submarine volcano located on the Juan de Fuca Ridge, approximately 480 km (298 mi) west of Cannon Beach, Oregon. Standing 1,100 m (3,609 ft) high, Axial Seamount is the youngest volcano and current eruptive center of the Cobb–Eickelberg Seamount chain. Located at the center of both a geological hotspot and a mid-ocean ridge, the seamount is geologically complex, and its origins are still poorly understood. Axial Seamount is set on a long, low-lying plateau, with two large rift zones trending 50 km (31 mi) to the northeast and southwest of its center. The volcano features an unusual rectangular caldera, and its flanks are pockmarked by fissures, vents, sheet flows, and pit craters up to 100 m (328 ft) deep; its geology is further complicated by its intersection with several smaller seamounts surrounding it.

Axial Seamount was first detected in the 1970s by satellite altimetry, and mapped and explored by Pisces IV, DSV Alvin, and others through the 1980s. A large package of sensors was dropped on the seamount through 1992, and the New Millennium Observatory was established on its flanks in 1996. Axial Seamount received significant scientific attention following the seismic detection of a submarine eruption at the volcano in January 1998, the first time a submarine eruption had been detected and followed in situ. Subsequent cruises and analysis showed that the volcano had generated lava flows up to 13 m (43 ft) thick, and the total eruptive volume was found to be 18,000–76,000 km3 (4,300–18,200 cu mi). Axial Seamount erupted again in April 2011, producing a mile-wide lava flow. There was another eruption in 2015.

Bocas de Fogo

Bocas de Fogo (Portuguese for "mouths of fire") is a volcano near the community of Urzelina, Velas municipality, São Jorge Island, Azores. It erupted in May and June 1808, causing destruction and over 30 deaths in Urzelina and producing a basalt field of volcanic rock extending to the Ponta da Urzelina. The eruption was the last sub-aerial event observed in the Azores; most recent eruptions have occurred along submarine vents, with the Capelinhos eruption (1957–58) starting as a submarine eruption (that eventually grew into a sub-aerial event) and the 1998–2001 Serreta eruption being exclusively submarine (never breaking the surface).

Bud Dajo

Bud Dajo (Tausug: Būd Dahu; Spanish: Monte Dajó), is the highest point in the province of Sulu, Philippines. it is one of the cinder cones that make up the island of Jolo and part of the Jolo Volcanic Group in the Republic of the Philippines. The extinct volcano is located 8 kilometres (5.0 mi) southeast from the town of Jolo in Sulu province. The mountain and adjacent lands were declared as Mount Dajo National Park in 1938.

Capelinhos

The Capelinhos (from Capelo + -inhos diminutive, which literally means "little cape") is a monogenetic volcano located on the western coast of Faial Island in the Azores. It is part of the larger volcanic complex of Capelo, which includes 20 scoria cones and lava fields that are aligned west-northwest to east-southeast from the Cabeço Gordo caldera. Although the name "Capelinhos" is associated with the volcano, it technically refers to the western cape of the parish of Capelo. It can be considered the westernmost point of Europe; there are more westerly islands in the Azores archipelago but they lie on the North American Plate.

A volcanic eruption lasted for 13 months, from September 27, 1957 until October 24, 1958, which may have been two overlapping volcanic eruptions. While enlarging the land by 2.4 km², it spawned 300 seismic events, hurled ash 1 km, destroyed 300 houses in the parishes of Capelo and Praia do Norte and caused the evacuation of 2,000 people (emigration to the US and Canada). On October 25, the volcano entered a period of dormancy. It is a part of an active fissural volcanic complex which creates multiple seismic and volcanic events.

Didicas Volcano

Didicas Volcano is an active volcanic island in the province of Cagayan in northern Philippines. The island, which was a submarine volcano and re-emerged from the sea in 1952, is 22 kilometres (14 mi) NE of Camiguin Island, one of the Babuyan Islands in Luzon Strait. Before 1952, the volcano first breached the ocean surface in 1857.

Jolo Group of Volcanoes

Jolo Group is an active group of volcanoes in the island of Jolo in Southern Philippines.

The Global Volcanism Program lists Jolo as one of the active volcanoes in the Philippines while the Philippine Institute of Volcanology and Seismology (PHIVOLCS) collectively list the group as Bud Dajo, one of the cinder cones on the island.

Kolbeinsey

Kolbeinsey (or, Kolbeinn's Isle, Seagull Rock, Mevenklint, Mevenklip, and Meeuw Steen) is a small islet 105 kilometres (65 mi) off the northern coast of Iceland, 74 kilometres (46 mi) north-northwest of the island of Grímsey. The island is the northernmost point of Iceland and lies north of the Arctic Circle. A basalt landform, devoid of vegetation, it is subject to rapid wave erosion and is expected to disappear in the near future, probably around the year 2020, based upon current rates of erosion.The original size of the island is unknown. When it was first measured in 1616, its size was 700 metres (2,300 ft) from north to south and 100 metres (330 ft) east to west. By 1903, it had already diminished to half that size. In August 1985, the size was given as 39 metres (128 ft) across. At the beginning of 2001, Kolbeinsey had reduced to an area of a mere 90 square metres (970 sq ft), which would correspond to the size of a circle of about 10.7 metres (35 ft) in diameter. The island has a maximum elevation of 8 metres (26 ft).

A helicopter landing site was constructed on the island in 1989 but efforts to strengthen the island have subsided in part because of agreements with Denmark over limits. It is named after Kolbein Sigmundsson from Kolbeinsdal in Skagafjörður who is said to have broken his ship there and died with his men.

Kuwae

Kuwae is a submarine caldera between the Epi and Tongoa islands in Vanuatu. Kuwae Caldera cuts through the flank of the Tavani Ruru volcano on Epi and the northwestern end of Tongoa.

The submarine volcano Karua, one of the most active volcanoes of Vanuatu, is near the northern rim of Kuwae Caldera.

Lava balloon

A lava balloon is a gas-filled bubble of lava that floats on the sea surface. It can be up to several metres in size. When it emerges from the sea, it is usually hot and often steaming. After floating for some time it fills with water and sinks again.

Lava balloons can form in lava flows entering the sea and at volcanic vents, but they are not common. They have been observed in the Azores, Canary Islands, Hawaii, Japan, Mariana Islands and Mexico. Apparently, they are generated when gases trapped within magma form large bubbles that eventually rise to the sea surface. In the Canary Islands, balloons containing sediments were used to infer the age of the basement on which the volcano is constructed; these sediments were also at first misinterpreted as evidence of an impending large explosive eruption.

Monte Brasil

Monte Brasil is the remnants of a tuff volcano (and peninsula) connecting the south coast of Terceira in the central Azores, overlooking the city of Angra do Heroísmo. Monte Brasil is flanked by two bays: the Bay of Angra (named for the city) to its east, and the Bay of Fanal to its west, and was used as a defensive point during the history of Angra, resulting in the construction of various forts and redoubts, including the Fortress of São João Baptista overlooking the city.

Sabrina Island (Azores)

Sabrina Island was an islet formed during the months of June and July 1811 by a submarine volcanic eruption off Ponta da Ferraria, São Miguel Island, Azores, one of many that have been felt in the Sete Cidades Massif over time. The first person to land in the new island was Commander James Tillard, captain of the British warship HMS Sabrina, who hoisted the Union Jack on the island and claimed sovereignty for Great Britain. A diplomatic row over the issue ensued, which the island's sinking back into the sea rendered moot.

Santorini caldera

Santorini caldera is a large, mostly submerged caldera, located in the southern Aegean Sea, 120 kilometers north of Crete in Greece. Visible above water is the circular Santorini island group, consisting of Santorini (aka Thera), the main island, Therasia and Aspronisi at the periphery, and the Kameni islands at the center.

Seamount

A seamount is a mountain rising from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to 1,000–4,000 m (3,300–13,100 ft) in height. They are defined by oceanographers as independent features that rise to at least 1,000 m (3,281 ft) above the seafloor, characteristically of conical form. The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea. During their evolution over geologic time, the largest seamounts may reach the sea surface where wave action erodes the summit to form a flat surface. After they have subsided and sunk below the sea surface such flat-top seamounts are called "guyots" or "tablemounts".There are more than 14,500 seamounts, of which 9,951 seamounts and 283 guyots, covering a total of 8,796,150 km2 (3,396,210 sq mi) have been mapped but only a few have been studied in detail by scientists. Seamounts and guyots are most abundant in the North Pacific Ocean, and follow a distinctive evolutionary pattern of eruption, build-up, subsidence and erosion. In recent years, several active seamounts have been observed, for example Loihi in the Hawaiian Islands.

Because of their abundance, seamounts are one of the most common marine ecosystems in the world. Interactions between seamounts and underwater currents, as well as their elevated position in the water, attract plankton, corals, fish, and marine mammals alike. Their aggregational effect has been noted by the commercial fishing industry, and many seamounts support extensive fisheries. There are ongoing concerns on the negative impact of fishing on seamount ecosystems, and well-documented cases of stock decline, for example with the orange roughy (Hoplostethus atlanticus). 95% of ecological damage is done by bottom trawling, which scrapes whole ecosystems off seamounts.

Because of their large numbers, many seamounts remain to be properly studied, and even mapped. Bathymetry and satellite altimetry are two technologies working to close the gap. There have been instances where naval vessels have collided with uncharted seamounts; for example, Muirfield Seamount is named after the ship that struck it in 1973. However, the greatest danger from seamounts are flank collapses; as they get older, extrusions seeping in the seamounts put pressure on their sides, causing landslides that have the potential to generate massive tsunamis.

Smith Island (Japan)

Smith Island, also known as Smith Rock (須美寿島, Sumisu-tō) is a volcanic, deserted island located in the Philippine Sea approximately 110 kilometres (68 mi) off the coast of Aogashima, near the southern end of the Izu archipelago, Japan.

Submarine volcano

Submarine volcanoes are underwater vents or fissures in the Earth's surface from which magma can erupt. Many submarine volcanoes are located near areas of tectonic plate formation, known as mid-ocean ridges. The volcanoes at mid-ocean ridges alone are estimated to account for 75% of the magma output on Earth. Although most submarine volcanoes are located in the depths of seas and oceans, some also exist in shallow water, and these can discharge material into the atmosphere during an eruption. The Kolumbo submarine volcano in the Aegean Sea was discovered in 1650 when it erupted, killing 70 people on the nearby island of Santorini. The total number of submarine volcanoes is estimated to be over 1 million (most are now extinct), of which some 75,000 rise more than 1 km above the seabed.Hydrothermal vents, sites of abundant biological activity, are commonly found near submarine volcanoes.

Volcanology of Italy

Italy is a volcanically active country, containing the only active volcanoes in mainland Europe. The country's volcanism is due chiefly to the presence, a short distance to the south, of the boundary between the Eurasian Plate and the African Plate. The magma erupted by Italy's volcanoes is thought to result from the subduction and melting of one plate below another.

Three main clusters of volcanism exist: a line of volcanic centres running northwest along the central part of the Italian mainland (see: Campanian volcanic arc); a cluster in the northeast of Sicily; and another cluster around the Mediterranean island of Pantelleria.

Zubair Group

Zubair Group, Al Zubair Group or Zubayr Group (Arabic: مجموعة جزر الزبير, or simply: جزر الزبير‎) is a group of 10 major volcanic islands, on top of an underlying shield volcano in the Red Sea, which reach a height of 191 m (627 ft) above sea level. The volcano has continued to erupt in historic times. The islands currently belong to Yemen.

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