Pillars at the Bottom of the Sea

Perched near the hot seams of some midocean ridges are curious pillars of lava, like Greek columns, many of them 45 feet tall. How these strange spires form has been unclear. Now volcanologists Tracy Gregg, at Woods Hole Oceanographic Institution, and William Chadwick, at Oregon State University, say these pillars were most likely created by the slow advances of lava oozing from volcanic ridges. Gregg and Chadwick developed a computer model of a lava flow from a midocean ridge. In their model, as the outer layers of lava blobs cool on contact with seawater, the interiors remain fluid. Sometimes three or four blobs nestle together in a ring, often leaving an empty, water-filled space at the center. The sides of these adjoining blobs eventually form the pillar walls, at least in the model. When the eruption fueling the blobs subsides, the lava inside each blob drains off, sometimes right back into the vent, as if someone pulled a plug in a bathtub, says Gregg. And the blobs, being relatively fragile, somewhat like big empty eggshells, collapse and leave standing behind as hollow pillars only the connected walls on the inside of the ring.