for National Geographic News
Billowing ash plumes, molten sulfur droplets, feisty shrimp feasting on fish killed by noxious gases, red lava jetting from a ventthey're all part of the action recently filmed at an underwater volcano in the western Pacific Ocean.
The images are the first ever direct observations of an active, submarine arc volcano. These volcanoes grow near trenches that form where one piece of Earth's oceanic crust slips beneath another.
(Related news: "Giant Deep Sea Volcano With 'Moat of Death' Found.")
Scientists dispatched remotely operated submarines to capture the images during three expeditions to the volcano, called Northwest Rota-1, in the Northern Mariana Islands near Guam (map of the South Pacific).
The latest expedition returned earlier this month.
"This is going to mean leaps in understanding these [underwater] volcanoes," said Robert Embley, a Newport, Oregon-based marine scientist with the U.S. National Oceanic and Atmospheric Administration.
Embley was a member of each expedition and is the lead author of a report on the March 2004 and October 2005 trips appearing in tomorrow's issue of the journal Nature.
Prior to the Mariana Islands expeditions, most submarine volcano research had occurred at mid-ocean ridges, Embley says. Mid-ocean ridges are mountain ranges that form in the deep ocean where new rock rising up from within the Earth forces apart seams in the planet's crust.
Unlike volcanic activity at mid-ocean ridges, island arc volcanoes can remain fixed over their magma sources for thousands of years, allowing them to sometimes grow above water level and become islands.
The new studies at the Mariana Islands are giving scientists a firsthand look into this formation process.
Northwest Rota-1 is a "typical" island arc volcano, Embley said. The cone-shaped mountain is about 10 miles (16 kilometers) in diameter at its base. The base is about 8,860 feet (2,700 meters) to 1,696 feet (517 meters) below sea level.
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