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Volcanos and Water

What happens when a volcano erupts underwater? Find out on this Moment of Science.

Firefighters use water to battle a towering inferno.You might wonder if water could also stifle an erupting volcano. Actually, this experiment happens every time a volcano erupts at the bottom of the ocean. What happens when a volcano erupts underwater?

Most of the world’s volcanic action happens an average of eight thousand five hundred feet underwater. Deep beneath the waves there are an estimated one million volcanos. As with land volcanos, molten lava pushes up from beneath the sea floor at thousands of degrees Fahrenheit.

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 volcanos 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.

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.

You can’t put out a volcano with water. But on our next program, we’ll find out what happened to a town that tried to do this anyway–and in a way succeeded!

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