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Deep-Sea Volcano Erupts on Film -- A First

John Roach
for National Geographic News
May 24, 2006
 
Billowing ash plumes, molten sulfur droplets, feisty shrimp feasting on
fish killed by noxious gases, red lava jetting from a vent—they'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.

Fundamental Findings

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.

The eruptions occur in the volcano's crater, a feature named Brimstone Pit, at 1,837 feet (560 meters) below sea level.

The volcano has been going through nearly constant low-level eruptions since at least 2004, when it was first observed, Embley says. It could potentially keep erupting for decades, giving scientists the opportunity to monitor its growth.

While the eruptions would be strong enough to send scientists running for cover on land, the pressure of water at Brimstone Pit dampens the explosive power, Embley explains, allowing scientists get up close with their cameras.

To date, the team has filmed billowing yellow plumes, droplets of molten sulfur, spewing rocks, landslides, a mysterious layer of cloudy water midway up the volcano, and red lava growing in the crater.

Extreme Life

In addition, the scientists have observed communities of microscopic bacteria and two species of shrimp living at the volcano.

The bacteria settle around vents that spew out hydrogen sulfide, a chemical that the life-forms convert into food, says Verena Tunnicliffe, a marine biologist at the University of Victoria in British Columbia, Canada.

"So that means there's an OK food source sitting there if you're able to live in an unstable, nasty place," she said.

"That's where the shrimp come in," Tunnicliffe added.

The juveniles of both shrimp species graze on the bacteria, which look like little hairs on rocks and other volcanic debris. One of the shrimp species' claws is shaped like tiny garden shears, Tunnicliffe says.

The adults of the other shrimp species eventually grow larger front claws and turn into carnivores. When Tunnicliffe first saw the second species in 2004, she thought the animals were there by some sort of accident. She didn't see much meat in the environment.

So she was surprised to see them in abundance again this year.

"At first we couldn't figure out what they were doing until a bunch swam by holding dead animals under their legs," she said.

The shrimp eat fish, other shrimp, and squid that are killed by the noxious volcanic gasses and then sink to the base of the volcano.

"These bottom shrimp are the garbage collectors of the deep," she said.

In future studies Tunnicliffe hopes to tease out what allows these shrimp to survive in an environment that is inhospitable to just about everything else.

"What are they doing that's different?" she said.

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