May 11, 2009

Background


This mission is aimed at exploring the sites of recent eruptions in the NE Lau Basin. The NE Lau Basin is located in the Southwest Pacific within the triangle formed by Samoa, Tonga and Fiji. This area is home to many submarine volcanoes and very few of them have ever been explored. In November 2008, the NOAA-PMEL Vents program discovered two on-going eruptions in this area, one at W. Mata Volcano and the other on the NE Lau spreading center (NELSC). West Mata volcano (~15̊.1 S, 173̊.7 W) appears to have formed on a tear in the ocean's crust, and may represent the initial stage of the formation of an arc volcano. It may also be producing unusual lavas (boninites) that previously have only been observed at old, inactive, volcanoes. The NELSC is a back arc ridge. An eruption along a back arc ridge has never before been detected, making this a valuable opportunity to explore newly formed ocean crust, hydrothermal vents, and biological communities.

We will explore the sites of these two eruptions from May 5th to May 13th, aboard the University of Washington’s Research Vessel T.G. Thompson. We will be using the Remotely Operated Vehicle (ROV) Jason 2 and the Autonomous Underwater Vehicle (AUV) D. Allan B. The Jason 2 will collect samples of rocks, hot spring waters, microbes, and macro biological specimens. The D. Allan B. will deliver high-resolution maps of the eruption sites.

This cruise represents an incredible opportunity to understand some exciting but unknown facets of our dynamic planet, Earth. Our planet is the most dynamic one in the solar system. Active volcanoes constantly build and reshape the Earth’s crust, providing energy and nutrients that nourish life. Strangely, while we visit our Moon, the planet Mars, and other planets, the submarine portions of our planet remain remarkably under-explored and therefore relatively unknown.

West Mata Volcano


West Mata volcano is located in an unusual location between the Tafua arc and the subducting trench. This volcano and its neighbors are elongate with two long rift zones running in the same orientation as the tears in the ocean crust beneath them. In November, W. Mata was draped in fresh clastic debris from its summit to its base, with old lava flows ponded at the ends of each of the rift zones. We are uncertain if magma from the back arc or the volcanic arc feeds W. Mata, although its location closer to the arc front suggests it is the dominant source. A rare lava type called boninite has been recovered in dredges in the area to the northwest of W. Mata. The eruption was discovered by detecting an intense cloud of particles rising ~175 m above its summit at 1200 m depth. We judged the volcano to be actively erupting during our sampling because the cloud contained enormous concentrations of hydrogen (> 9000 nM) and abundant sharp-edged rock shards. Extremely high levels of hydrogen are generated when molten rock and water come in contact. The rocks then explode into countless pieces (or clasts), and the finest of these particles rise with the cloud. The same process forms the ash clouds commonly seen over erupting volcanoes on land. Many of these characteristics are similar to those at NW Rota-1 in the Mariana arc, which has been undergoing continuous submarine eruption for at least 5 years. The summit of W. Mata is about 800 m deeper than NW Rota-1 so eruptive processes are likely to differ due to the greater pressures at W. Mata.

Northeast Lau Spreading Center (NELSC)



The NE Lau spreading center is located on a spreading ridge in a back arc basin and its eruption would represent the first documented eruption in this setting. Our first clues that unusual activity was taking place along this volcanic ridge were the observations of clouds of particles (plumes) rising 800-1000 m above the sea floor. These plume rise heights are a strong indicator of seafloor eruptions, and, as at W. Mata, the plumes contained elevated levels of hydrogen and high concentrations of volcanic glass shards. This site differs from West Mata in that it is part of a semi-continuous system of back-arc “spreading centers” that have been forming in the Lau Basin as the result of the subducting plate to the east pulling away from the Australian plate to the west. These spreading centers generate new ocean crust just as happens along the globe-encircling Mid-Ocean Ridge, but we know little about the volcanic and hydrothermal systems that drive their formation and the biologic systems that feed off the hot hydrothermal effluent. This expedition will be the first to investigate a newly erupted site on a back-arc spreading center where the geologic and biologic “clock” has been “reset” by an eruption, and, like similar studies at the Mid-Ocean Ridge over the past 20 years, we will very likely be surprised and excited by what we will find.


video
3-D fly-through over Northeast Lau Basin. The EM300 bathymetry (colored) were collected on the November expedition. The data are 1.5 times vertically exaggerated. The fly-through starts at the southern end of the NELSC heading north along the spreading center. Then the flight zooms in on West Mata, approached from the south and then circling around to the north. The final image is looking from the north toward the south.