An Undersea Eruption

Oregon State University Marine Geologist Bill Chadwick sat aboard the National Oceanic and Atmospheric Administration (NOAA) ship Okeanos Explorer near Guam, watching the video feed from the ship’s robotic vehicle Sentry. Five kilometers below, the drone cruised above the surface of an undersea volcano of the Mariana back-arc. Although Sentry’s lamps were the first light that had ever fallen on the surface of those undersea mountains, Chadwick knew that if he found a volcanic hot spring, he was likely to find life, an exotic life which thrives in the alien environment of the deep ocean.

Chadwick was not anticipating what happened next. Sentry passed above a field of fresh lava, so new it had not yet been covered by sediment. The extreme water pressure at that depth doesn’t allow lava to boil the water around it, so a deep-sea lava flow does not form the familiar rough pitted landscape. What Chadwick saw was a vast glassy-smooth surface.

“We weren’t expecting to find a recent eruption where we were working, near a subduction plate boundary,” Chadwick said, adding that “We were looking for hot springs, but we found this recent eruption site. We don’t think they happen all that often, probably only every hundred years or so. We think this happened only a couple of months ago.”

Beyond the rare opportunity to study a fresh eruption site, Chadwick made surprising discoveries about thermal vent communities.

“This area’s pretty interesting to us, because of these two chains of volcanoes north of Guam, cones both shallow and deep, very different kinds of eruptions.” Since each thermal vent releases its own mix of chemicals, in its own quantities, at its own temperature, each thermal vent ecosystem is different. Chadwick has found that small differences produce surprising differences in communities. “The geological setting is controlling the animals very closely.”

Everybody likes a good undersea volcanic eruption, but for Chadwick, the differences between the little vent communities are where the real action lies. He’s looking forward to exploring more thermal vent communities, each one almost a world of its own.

By John M. Burt