Volcanic mysteries unraveled underwater

Almost all of the active volcanoes on Earth lie beneath miles of seawater at mid-ocean ridges, creating the long chain of volcanic mountains that encircles the Earth like the seam of a baseball. Scientists have long been puzzled by the observation that flows, erupted as white-hot lava at mid-ocean ridges, can be traced for several miles from their vents despite the fact that they erupt into seawater close to its freezing point. Now a group of scientists from academia and government believe they have the answer from lava samples collected using the deep-sea submersible ALVIN.

In the most recent issue of the magazine Nature, scientists from the U.S. Geological Survey (USGS) and an international group of university researchers report that the tops of the lavas chill against cold seawater protecting the molten interior, which moves forward on a thin film of vaporized seawater much like a hydrofoil. The seawater steam also bubbles through the lava and forms large cavities within the flowing, white hot material. Because of the high pressures, these cavities later collapse, producing a “swiss cheese” texture on the surface of the lava flow.

A critical piece of evidence came through very high magnification images of the insides of these cavities, using a sophisticated scanning electron microscope at the USGS in Denver, Colo. The images showed the presence of molten salt and many exotic minerals that could only have formed from vaporized seawater at very high temperatures.

“Previously, scientists had thought that seawater could never boil at the great depths of mid-ocean ridges but now it appears that hot vaporized seawater plays a major role in building new oceanic crust”, said Dr Ian Ridley, a co-author on the Nature report, and a research scientist with the USGS.