Spreading ridges volcanoes map
Map of world's major seamounts
Map of world's major hotspots
Submarine volcanoes are underwater fissures in the Earth's surface from which magma can erupt. They are estimated to account for 75% of annual magma output. The vast majority are located near areas of tectonic plate movement, known as ocean ridges.
Although most are located in the depths of seas and oceans, some also exist in shallow water, which can spew material into the air during an eruption. Hydrothermal vents, sites of abundant biological activity, are commonly found near submarine volcanoes.
The presence of water can greatly alter the characteristics of a volcanic eruption and the explosions made by these. For instance, the increased thermal conductivity of water causes magma to cool and solidify much more quickly than in a terrestrial eruption, often turning it into a volcanic glass.
Below ocean depths of about 2200 meters where the pressure exceeds 218 atmospheres, the critical pressure of water, it can no longer boil; it becomes a supercritical fluid. Without boiling sounds, deep-sea volcanoes are difficult to detect at great distances using hydrophones.
The lava formed by submarine volcanoes is quite different from terrestrial lava. Upon contact with water, a solid crust forms around the lava. Advancing lava flows into this crust, forming what is known as pillow lava.
Scientists still have much to learn about the location and activity of underwater volcanoes. The Kolumbo underwater volcano in the Aegean Sea was discovered in 1650 when it burst from the sea and erupted, killing 70 people on the nearby island of Santorini.
More recently, NOAA's Office of Ocean Exploration has funded missions to explore submarine volcanoes. Most notably, these have been the Ring of Fire missions to the Mariana Arc in the Pacific Ocean. Using Remote Operated Vehicles, scientists studied underwater eruptions, ponds of molten sulfur, black smoker chimneys and even marine life adapted to this deep, hot environment.
Many submarine volcanoes are usually found as seamounts. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of 1,000 - 4,000 meters depth. They are defined by oceanographers as independent features that rise to at least 1,000 meters above the seafloor. The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep 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, the Bowie Seamount in Canada's Pacific waters rises from a depth of about 3,000 meters to within 24 meters of the sea surface.
Weird Underwater Volcano Discovered Near Baja Live Science - December 14, 2012
Scientists have discovered one of the world's weirdest volcanoes on the seafloor near the tip of Baja, Mexico. The petite dome - about 165 feet tall (50 meters) and 4,000 feet long by 1,640 feet wide (1,200 m by 500 m) - lies along the Alarcon Rise, a submarine depression located on the seabed at the southern end of the Gulf of California. Tectonic forces are tearing the Earth's crust apart at the spreading center, creating a long rift where magma oozes toward the surface, cools and forms new ocean crust. Circling the planet like baseball seams, seafloor-spreading centers (also called midocean ridges) produce copious amounts of basalt, a low-silica content lava rock that makes up the ocean crust. (Silica, or silicon dioxide, is the main component of quartz, one of the most common minerals on Earth.)
Rise and fall of underwater volcano revealed BBC - May14, 2012
The violent rise and collapse of an underwater volcano in the Pacific Ocean is captured in startling clarity for the first time. Researchers studying the Monowai volcano, near Tonga, recorded huge changes in height in just two weeks.
Pictures: Undersea Volcano Erupts, Stains Seas National Geographic - October 21, 2011
Whitecaps churn in the Atlantic off West Africa as an underwater volcano erupts off Spain's Canary Islands on Monday. Since last week, the volcano has been spewing gas and fragments of smoking lava, staining the ocean surface green and brown, as seen above. Spanish authorities have closed a port on Hierro island (map), ordered ships away from the island's village of La Restinga, and banned aircraft from flying over the island's southern tip, according to the AFP news service.
Deep-sea volcanoes don't just produce lava flows, they also explode PhysOrg - March 28, 2011
Most deep-sea volcanoes produce effusive lava flows rather than explosive eruptions, both because the levels of magmatic gas tend to be low, and because the volcanoes are under a lot of pressure from the surrounding water.
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