The red arc of seamounts shows the Mariana volcanoes under study. The dark blue color indicates the Mariana trench, the deepest place on the planet.

Current expedition:
April 2009 cruise to NW Rota-1
This expedition focused on NW Rota-1, the only known actively erupting undersea volcano. Dives with the ROV Jason made observations of the activity, collected samples, and deployed instruments that will monitor the activity over the next year.

The Mariana Volcanic Arc extends from 13°N to 23°N in the western Pacific Ocean, northwest of Guam. The Marianas region contains 9 volcanic islands more than 50 submarine volcanoes over a distance of more than 1000 km. The summits of these submarine volcanoes range from 50 m to more than 1800 m below sea level. The Marianas is one of the most active volcanic arcs on Earth.

In February 2003, the Vents Program conducted an extensive survey of the submarine volcanoes in the Mariana Arc (funded in part by NOAA's Ocean Exploration Program). This expedition included detailed mapping of the seafloor and a search for indications of hydrothermal venting at each volcano. It was found that about 20% of the Marianas submarine volcanoes were hydrothermally active. A follow up expedition with a remotely operated vehicle will investigate these sites on the seafloor.

For more information on the Marianas see:

2009:
Vents Expedition to NW Rota (blog website)
2006:
Ocean Exploration Ring of Fire website
2004:
Ocean Exploration Ring of Fire website
Cruise report (pdf)
Multimedia gallery (Vents Program | Ocean Explorer)
2003:
Ocean Exploration Ring of Fire website
Cruise report (pdf)
Expedition photo and video log

References:

NW Eifuku:
Survival of mussels in extremely acidic waters on a submarine volcano
Verena Tunnicliffe1,2, Kimberley T. A. Davies1,6, David A. Butterfield3, Robert W. Embley4, Jonathan M. Rose1 & William W. Chadwick Jr5 , Nature Geoscience, Published online: 12 April 2009

updated 4/2009