Some of the biggest volcanoes on Earth have never been seen by any human. That’s because they’re more than a mile underwater. You’d have to dive down a mile and a half just to reach the tops of these volcanoes. This string of underwater volcanoes is called the Mid-Ocean Ridge.

The Mid-Ocean Ridge (the dotted line) winds its way between the continents much like the seam on a baseball.

Click on the image to enlarge

The Mid-Ocean Ridge is the biggest mountain range on our planet. It’s more than 30,000 miles long and almost 500 miles wide. Its hundreds of mountains and volcanoes zigzag under the ocean between the continents, winding their way around the globe like the seam on a baseball. That means there are underwater mountains and volcanoes all around the world. Nearly every day, at least one underwater volcano erupts. Super-hot lava pours out of the volcano and onto the ocean floor. This underwater lava is called pillow-lava because it looks like big puffy pillows.

Click on the image to enlarge

The bottom of the sea is always changing. Super-hot lava erupts from deep inside the earth. Then the lava cools, forming rocks. Layers of rocky lava pile up. Over millions of years, all that lava makes the sea floor expand. As the sea floor expands, it pushes the continents around. A million years ago, the Earth looked very different than it does today. A million years from now, it will have changed even more.

Scientists called marine geologists are learning more about undersea volcanoes every day. You can too. Try the experiment on the next page!

Contents • Cool Science Stuff • find out why