May 11, 2009

West Mata Eruption Comparisons

Dave Clague

The two Jason dives at West Mata volcano discovered not just one active volcanic vent, but two. The first and deeper vent, named Hades vent, on the southwest rift was erupting both effusively and explosively at the same time on both days. Small bursts were occurring at one end of an erupting fissure perhaps 5 meters long while pillow lavas were being extruded from the other end. By the next night the activity had become more vigorous, sometimes blowing glowing bubbles as much as a meter across. The second shallower vent, named the Prometheus, was located very near the summit of the volcano and about 100 meters away from the first vent. The eruption here was entirely explosive with low-level, but nearly continuous fire fountains throwing ejecta into the water during both dives. Both vents were obscured much of the time by billowing sulfurous gas emissions, but bright orange lava was seen in both vents. The orange glowing lava was visible for minutes at a time. Clear carbon dioxide bubbles were not observed at or near the vents, in contrast to their abundance at NW Rota-1 volcano in the Marianas arc, which was visited just last month by many on board this expedition.