(Intro)

You know, nature can create some pretty amazing stuff. We've got waterfalls and mountains and beaches and canyons. A canyon is a deep gorge or gully in the Earth. It usually has steep walls and most of the time there's a river flowing at the bottom of it. And, one of the biggest canyons in the world is in the southwestern United States, the Grand Canyon in Arizona.

How grand is the Grand Canyon? Well, say you took the tallest building in the world and stacked it on top of itself twice. The Grand Canyon is deeper than that, and it's also more than 450 kilometers long, that's about four days to walk its length from end to end.

So, how did this giant groove in the Earth get there? You can see the secret in this picture. Do you notice anything besides the Grand Canyon in this photo? How about at the bottom? That's right, water! That's a river, called the Colorado River, and it's what carved the Grand Canyon that we know today.

How did it do that? Very slowly. A long time ago, the land where the Grand Canyon is was just a big, flat landscape, but then water started to flow. The water flowed over the plain, picking up little pieces of dirt and rock as it went along. The water carried the stuff from one place to another, moving it downstream. It happened just one tiny piece at a time, but over a really, really long time it made a big difference. The natural process of dirt and rock getting picked up from one place and moved to another is called erosion. And, you've probably seen it happen. Have you ever built a sandcastle at the beach, and then watched as a wave crashed over it and moved the sand? The water eroded your castle, but rocks are a lot harder to break down than a sandcastle so it takes a lot more time. A river can create something a big and breathtaking as the Grand Canyon, because a river is always moving, so it's always eroding the rock.

And sometimes, special things happen to really speed things up, like a flood. When a river floods way more water flows into the river than it usually holds, and the river starts to overflow. And, when more water rushes through a river, that means it can pick up more stuff. A big flood can even move big, heavy rocks and carry them down along the river, and all of these big, moving rocks can act like chisels, carving away at the land. And a series of big floods, just like that, made the Grand Canyon deeper and deeper.

But the Grand Canyon isn't just deep, it's wide, too. What makes it so wide? Erosion again and water again, but this time it's rain water. When it rains, water flows down from the sides of the canyon acting like a bunch of teeny tiny rivers picking up more pieces of rock and making the canyon wider. Today, the Grand Canyon is almost 30 kilometers across at its widest point. That's like 30 football fields.

But, even with the occasional big flood or heavy rain, it still takes a really, really long time to make a canyon as long and wide and deep as the Grand Canyon. Scientist are pretty sure that the canyon started forming 5 to 6 million years ago. So, erosion happens very slowly. Sometimes it happens so slowly, we can't even see it working, but sometimes we can! When you see a rock moving with the water in a stream, that's erosion. When you see a river full of muddy water, that's erosion too. All those pieces of dirt in the river are flowing with the water moving from one place to another.

And, since the Colorado River is still flowing, erosion is still happening which means the Grand Canyon is still growing, kind of like you. Thanks for joining us on SciShow Kids. Do you have a question about space or animals or anything else? Get help from a grownup, and let us know in the comments below or send us an email to kids@theSciShow.com and we'll see you next time.