Submarine volcano

Not to be confused withSubaqueous volcano,a volcano formed beneath freshwater that never builds above lake level.

For mountains rising from the ocean seafloor, seeSeamount.For related geological features, seeMid-ocean ridgeandHotspot (geology).

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

Pillow lava formed by a submarine volcano

NOAAexploration video showing remnants of underwatertarvolcanoes.

Circular plumes from a submarine eruption nearTonga

Submarine volcanoesare underwater vents or fissures in theEarth's surface from whichmagmacan erupt. Many submarinevolcanoesare located near areas oftectonic plate formation,known asmid-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 ofseasandoceans,some also exist in shallow water, and these can discharge material into the atmosphere during aneruption.The total number of submarine volcanoes is estimated to be over one million (most are now extinct) of which some 75,000 rise more than 1 kilometre (0.62 miles) above theseabed.Only 119 submarine volcanoes in Earth's oceans and seas are known to have erupted during the last 11,700 years.

Hydrothermal vents,sites of abundant biological activity, are commonly found near submarine volcanoes.

Effect of water on volcanoes

The presence of water can greatly alter the characteristics of a volcanic eruption and the explosions of underwater volcanoes in comparison to those on land.

For instance, water causes magma to cool and solidify much more quickly than in a terrestrial eruption, often turning it intovolcanic glass.The shapes and textures of lava formed by submarine volcanoes are different from lava erupted on land. Upon contact with water, a solid crust forms around the lava. Advancing lava flows into this crust, forming what is known aspillow lava.

Below ocean depths of about 2,200 metres (7,200 ft) where the pressure exceeds thecritical pressureof water (22.06MPaor about 218atmospheresfor pure water), it can no longer boil; it becomes asupercritical fluid.Without boiling sounds, deep-sea volcanoes can be difficult to detect at great distances usinghydrophones.

The critical temperature and pressure increase in solutions of salts, which are normally present in the seawater. The composition of aqueous solution in the vicinity of hot basalt, and circulating within the conduits of hot rocks, is expected to differ from that of bulk water (i.e., of sea water away from the hot surfaces). One estimation is that the critical point is 407 °C (765 °F) and 29.9 MPa, while the solution composition corresponds to that of approximately 3.2% of NaCl.

Research

Scientists still have much to learn about the location and activity of underwater volcanoes. In the first two decades of this century, NOAA'sOffice of Ocean Explorationhas funded exploration of submarine volcanoes, with the Ring of Fire missions to the Mariana Arc in the Pacific Ocean being particularly noteworthy. Using Remote Operated Vehicles (ROV), scientists studied underwater eruptions, ponds of moltensulfur,black smokerchimneys and even marine life adapted to this deep, hot environment.

Research from the ROV KAIKO off the coast of Hawaii has suggested that pahoehoe lava flows occur underwater, and the degree of the submarine terrain slope and rate of lava supply determine the shape of the resulting lobes.

In August 2019, news media reported a largepumice raftfloating in the South Pacific between Fiji and Tonga.Subsequent scientific investigations revealed the pumice raft originated from the eruption of a nearby submarine volcano, which was directly observed as avolcanic plumein satellite images.This discovery will help scientists better predict for the precursors of a submarine eruption, such as low-frequency earthquakes orhydrophonedata, usingmachine learning.

Seamounts

Many submarine volcanoes areseamounts,typicallyextinct volcanoesthat rise abruptly from a seafloor of 1,000 metres (3,300 ft) - 4,000 metres (13,000 ft) depth. They are defined byoceanographersas independent features that rise to at least 1,000 metres (3,300 ft) above the seafloor. The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within thedeep sea.An estimated 30,000 seamounts occur across the globe, with only a few having been studied. However, some seamounts are also unusual. For example, while the summits of seamounts are normally hundreds of meters below sea level, theBowie Seamountin Canada's Pacific waters rises from a depth of about 3,000 metres (9,800 ft) to within 24 metres (79 ft) of the sea surface.

Identifying types of eruptions by sounds

Deepest ever filmed submarine volcano,West Mata,May 2009.

There are two types of sound generated by submarine eruptions: One created by the slow release and bursting of large lava bubbles, while quick explosions of gas bubbles create the other one. Using this method to be able to distinguish the two can help measure the related affects on marine animals and ecosystems, the volume and composition of the lava flow can also be estimated and built into a model to extrapolate potential effects.

Scientists have connected sounds to sights in both types of eruptions. In 2009, a video camera and a hydrophone were floating 1,200 metres (3,900 ft) below sea level in the Pacific Ocean near Samoa, watching and listening as theWest Mata Volcanoerupted in several ways. Putting video and audio together let researchers learn the sounds made by slow lava bursting and the different noises made by hundreds of gas bubbles.

See also

• List of submarine volcanoes

External links

• Volcano Information from the Deep Ocean Exploration Institute,Woods Hole Oceanographic Institution
• Volcano World- now maintained by the Department of Geosciences at Oregon State University
• Britannica - Submarine Volcanoes
• United States Geological Survey
• Ring of Fire Exploration Mission