The Puipui eruption of Northeast Lau spreading center
Most of Earth’s volcanic activity happens beneath the sea, sight unseen, sound unheard. It’s really rare to witness these eruptions, either accidentally or by design, so when marine scientists catch a whiff of one, we’ll go to extraordinary lengths to locate and observe it. Five months after the email message came in that the NOAA Vents group had discovered spectacular particle plumes rising up to 600 m (~2000 ft) above the sea bed at a site in the Northeast Lau Basin, here we are, looking for the eruption that made them. It turned out there were two eruption sites, one of which is still active, at West Mata volcano and one which is not, at the Northeast Lau Spreading Center (NELSC). Both sites are fascinating places to work. At NELSC, where some might see a seemingly endless sheet of dull black rock that isn’t moving and glowing anymore, isn’t venting hot water, and isn’t teeming with animals, the geologist in me sees cascading lava falls and swirling sheets and rivers of liquid hot magma.
We are calling the NELSC lava flow “Puipui”, meaning curtain in Tongan, because of the distinctive way the lava draped and folded itself over the landscape. The Puipui eruption is interesting because of the range of lava forms we observed over short spatial distance, which resulted from a combination of steep topography, gas rich and fluid magma, and what was apparently an intensely fast lava effusion event. Driving Jason along the lava flow, we saw first hand how important the pre-eruption land surface was for controlling where and how the young lava flowed. It only took 4 to 5 feet tall ridges of old rock to dam the Puipui lava flow in places, where it flowed in thin flat sheets between the high ground. Nearer the volcanic vents, which appear to sit along a narrow ridge, lava cascaded 30 feet or more down steep rock faces, forming sheets of lavas that look like curtains draped over the sea floor. In other places, the lava ponded, crusted over on top, and then drained out, leaving collapse pits that reveal hollow chambers roofed by lava shells held up by pillars of fresh lava rock.
We’re done observing Puipui for now, but the real work has yet to come. There are maps to pour over, and a hundred or so pounds of rocks to take back to the lab. The rocks will be used to learn how magmas form in this location and when they erupted, which will help us understand a little more about deep submarine eruptions.
All high-definition video by Advanced Imaging and Visualization Lab, copyright WHOI