Side view of a collapsed lava pit on the East Pacific Rise near 9°50N at a depth of 2,500 meters (about 8,000 feet). Two lava pillars in the center of the photo support a piece of the upper crust of the lava flow several inches thick.
Underside of a piece of lava from the East Pacific Rise showing drip structures or stalactites. The sample is about eight inches across, with individual lava drips of about one to two inches in length.
Photos ©Woods Hole Oceanographic Institution
Scientists studying the formation of the sea floor thousands of feet below the surface have a new theory for why there are so many holes and collapsed pits on the ocean bottom. In a recent article in the journal Nature, the researchers say the holes and pits of various sizes are probably formed by lava erupting onto the seafloor so quickly it traps water beneath it, forming bubbles of steam that eventually collapse as the water cools. The hardened crust then breaks, forming pock marks and glassy black plates of ocean crust with stalactites on their underside.
Findings by scientists at the Woods Hole Oceanographic Institution (WHOI) and colleagues may help explain the chemical differences between some seafloor lavas and increase understanding of deep-sea volcanic processes. The report also offers new insights into microbes living inside the ocean crust, an area known as the deep biosphere. No one has witnessed an undersea volcanic eruption, although researchers diving in the three-person submersible ALVIN have visited sites of very recent eruptions that were colonized almost immediately by exotic life forms.
Geologists Daniel Fornari and Deborah Smith of WHOI, along with lead author Michael Perfit of the University of Florida and colleagues from the University of Leeds in the United Kingdom, University of Hawaii and the US Geological Survey, report that up to now, scientists thought there was very little interaction between the very cold sea water at the ocean floor several miles deep and the molten lava that erupts to form new crust. Geologists didn’t think the lava, despite reaching temperatures well over 2,000 degrees Fahrenheit, could heat the seawater enough to form steam because of the intense pressure at such great depth.
Shelley Dawicki | WHOI
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