General features of the ocean basins. Compare with the tectonic map.
The most productive volcanic systems on Earth are hidden under an average
of 8,500 feet (2,600 m) of water. Beneath the oceans a global system of
mid-ocean ridges produces an estimated 75% of the annual output of magma. An
estimated 0.7 cubic miles (3 cubic kilometers) of lava is erupted. The magma
and lava create the edges of new oceanic plates and supply heat and chemicals
to some of the Earth's most unusual and rare ecosystems.
Contact between young pillow lavas erupted in mid-1980s and older lavas with light dusting of sediment.
Hand-held photo from submersible Alvin taken on Cleft segment of southern Juan de Fuca Ridge.
Photo by Bill Chadwick of NOAA and Oregon State University.
If an estimate of 4,000 volcanoes per million square kilometers on the floor
of the Pacific Ocean is extrapolated for all the oceans than there are more
than a million submarine (underwater) volcanoes. Perhaps as many as 75,000
of these volcanoes rise over half a mile (1 kilometer) above the ocean floor.
Technology and hard work by a group of tenacious explorers/geologists have
allowed us our first detailed glimpses of submarine volcanoes. The following
pages outline some of the basic characteristics and features of submarine