Map of West and East Mata Volcanoes.

2008 Expedition to Lau Basin

November 25, 2008

One of the things we do aboard ship to help understand the systems we are studying is to measure the concentrations of hydrogen and methane dissolved in the plume water samples we collect. These two gases typically have different origins in sea-floor hydrothermal systems. Hydrogen is produced by reactions between the host rock and hot seawater. Usually the hotter the water and the deeper the reaction occurs, the more hydrogen produced. Methane, on the other hand, is usually low in hot hydrothermal fluids and higher in low temperature fluids where it is produced by microorganisms.

On this cruise, we have seen a huge variation in the concentrations of these two gases. Early in the cruise we saw very high concentrations of hydrogen above the North East Lau Spreading Center (NELSC) which indicated that it was either erupting at the moment or had erupted in the very recent past. Most recently, we have been investigating two small volcanoes (East Mata and West Mata), which have very different concentrations of these gases. West Mata has about three times as much hydrogen in the plume water as we saw over the NELSC and is the world record for those of us aboard the Thompson. East Mata, on the other hand, has almost undetectable hydrogen but high concentrations of methane. Our tentative conclusion is that these two small volcanoes, which are only seven kilometers apart, are in different stages of their eruptive cycles with West Mata having erupted very recently.

Marv Lilley , Hydrothermal Plume Studies

updated 1/14/2009