Ocean water can’t “put out” the volcano the way firefighters put out a fire, but it does have a profound effect on what happens to the lava once it’s out of the ground. The biggest difference between undersea and land volcanoes has nothing to do with water’s wetness, but with its pressure. At these depths, the water pressure can be two hundred and fifty times more powerful than air pressure at the Earth’s surface. This prevents bubbles from forming in the lava, eliminating the likelihood of an explosive eruption like some land eruptions are. Instead, lava squeezes out of the ground like toothpaste out of a tube, forming glassy rock formations that look like long, stacked pillows. The pressure is so high that steam never even forms where lava touches water. You could be in a boat over a giant, erupting volcano, and never even know it was there.