Submarine Volcanoes
Submarine volcanoes and volcanic vents are common features on certain zones of the ocean floor.
Some are active at the present time and, in shallow water, disclose their presence by blasting steam and rock-debris high above the surface of the sea.
Many others lie at such great depths that the tremendous weight of the water above them results in high, confining pressure and prevents the formation and explosive release of steam and gases.
Even very large, deepwater eruptions may not disturb the ocean surface.
The unlimited supply of water surrounding submarine volcanoes can cause them to behave differently from volcanoes on land.
Violent, steam-blast eruptions take place when seawater pours into active shallow submarine vents.
Lava, erupting onto a shallow sea floor or flowing into the sea from land, may cool so rapidly that it shatters into sand and rubble.
The result is the production of huge amounts of fragmental volcanic debris.
The famous "black sand" beaches of Hawaii were created virtually instantaneously by the violent interaction between hot lava and seawater. Loihi Submarine Volcano - the most recent expression of the hotspot that produces the Hawaiian Island chain - NOAA
On the other hand, recent observations made from deep-diving submersibles have shown that some submarine eruptions produce flows and other volcanic structures remarkable similar to those formed on land.
During an explosive submarine eruption in the shallow open ocean, enormous piles of debris are built up around the active volcanic vent.
Ocean currents rework the debris in shallow water, while other debris slumps from the upper part of the cone and flows into deep water along the sea floor.
Fine debris and ash in the eruptive plume are scattered over a wide area in airborne clouds.
Coarse debris in the same eruptive plume rains into the sea and settles on the flanks of the cone.
Pumice from the eruption floats on the water and drifts with the ocean currents over a large area.
Europe's largest underwater volcano is active according to the scientists who have been monitoring it for years, but until recently believed it to be dormant. There has never been an eruption of the volcano in recorded history. The Tyrrhenian Project, the national research group studying the volcano, reported its findings last November 27, 1999.
Mt. Marsili, which rises 9,800 feet (3,000 meters) from the seabed in the Tyrrhenian Sea southwest of Naples, is capable of producing huge tidal waves along southern Italy if its activity ever does build to an eruption. According to the researchers, "Il Marsili'" is about 40 miles (65 km) long and 25 miles (40 km) wide. The experts said its tip was only 1,640 feet (500 metres) below the surface of the water.
Michael Marani, the scientist heading up the study of the volcano, said, "Because the Tyrrhenian Sea is the youngest sea in the Mediterranean, it is still unstable and carries elevated risks that must be monitored and understood." He reported that evidence of enormous masses which had probably broken away from the main crater a long time ago were found on the volcanic edge.
Sicily - Volcano larger than Washington, D.C., discovered CNN - June 23, 2006
Legend has it that the philosopher died by throwing himself into Mount Etna, the nearby Sicilian volcano. Giovanni Lanzafame, who works at the institute and led the research, said Empedocles was at least 400 meters (1,300 feet) high -- taller than the Eiffel Tower. The base of the structure was 30 km (18.6 miles) long and 25 km wide, spanning an area larger than the U.S. capital and making it Italy's largest underwater volcano.
But Lanzafame said Sicilians did not need to worry about the sleeping Empedocles. "At this point, there's no imminent danger of an eruption," he told Reuters. Lanzafame and another official said the volcano had numerous fumaroles, openings in the Earth's crust that emit steam and gases, like the ones at Yellowstone National Park in the United States. But they described it as largely inactive.The identification of Empedocles came during research into the submerged volcanic island of Ferdinandea just off Sicily's southern coast. Often held to be the tip of a small volcano, Lanzafame said it was just a part of Empedocles. Volcanic activity has raised the island out of the sea several times in recorded history, with underwater eruptions first described during the first Punic War of 264-241 B.C. Its emergence in 1831 caused months of international wrangling, with several nations making territorial claims before it submerged again. It is now about 7 meters below the surface of the water.
Underwater Volcano Erupts on Video National Geographic - May 25, 2006
A volcano is seen erupting 1,800 feet beneath
the surface of the Pacific Ocean near Guam.
Unraveling the Mysteries of Underwater Volcanoes NOAA - August 21, 2001
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