The longest mountain range on Earth is called the mid-ocean ridge. Spanning 40,389 miles around the globe, it's truly a global landmark.
About 90 percent of the mid-ocean ridge system is under the ocean. This system of mountains and valleys criss-crosses the globe, resembling the stitches in a baseball. It's formed by the movement of the Earth's tectonic plates.
As the great plates push apart, mountains and valleys form along the sea floor as magma rises up to fill the gaps. As the Earth's crust spreads, new ocean floor is created. This process literally renews the surface of our planet.
If you look at a map of the world's volcanoes, you'll find that most of them form along the boundaries of this great system. In fact, the global mid-ocean ridge system forms the largest single volcanic feature on the Earth. The mid-ocean ridge consists of thousands of individual volcanoes or volcanic ridge segments which periodically erupt.