字幕表 動画を再生する 英語字幕をプリント Squeaks and I live right near a river. It's fun to watch the water rush past, and sometimes people even go fishing in it! Like most of the rivers in the world, it flows downhill, right along the ground. But did you know that some rivers flow right off of cliffs? Just look at this one! This is a river that's flowing right off a cliff, and that's what we call a waterfall. This waterfall is called Angel Falls. It's in Venezuela, in South America, and it's the tallest waterfall in the world! It's almost 1000 meters tall. That's taller than the tallest building! Waterfalls start off as normal rivers, with lots of water flowing towards one place. But then the water in the river comes to a cliff. It flows over the side and becomes a waterfall! In the case of Angel Falls, it becomes a huge waterfall. But the cliff hasn't always been there. The river actually built the cliff. [Squeaks squeaks] No, really! Where there's now a huge cliff? That used to just be regular flat ground with the river flowing over it. But if you looked underneath this river, you'd find a layer of hard rock, then a layer of softer rock or dirt, then another layer of hard rock, over and over in a pattern! It looks almost like a cake with lots of layers! Some of the parts of the river hit only the hard layers, but the water eventually hits some of the softer layers. That's where the water can do some real work. When water goes over rocks, it can wear away at those rocks over time. We call this erosion. It's easier to for the water to erode soft things than hard things, like how it's easy for you to smash a sand castle, but harder for you to break a brick. So, as the water goes over the hard rock, it doesn't do too much. But as it goes over the soft rock, it wears away the layer of soft rock more quickly. The water takes a few little pieces of rock away, then a few more, and more, until finally, the soft rock layer is gone. When the layer of soft rock is completely eroded away, that creates a cliff between two of the layers of hard rock. This takes a very, very long time to happen, sometimes millions of years. [Squeaks squeaks] Exactly! The water flows over the top of the cliff and falls straight down as a waterfall. Angel Falls has grown especially tall because of how the water and the rock interact. The land around Angel Falls has layers of very soft rock that erode super easily, and tons of incredibly hard rock that hardly erodes at all. Because of the big difference in how these layers erode, this river has carved a huge amount of soft rock out of the way, and very little hard rock. That created the tallest waterfall in the whole world! Thanks for joining us on SciShow Kids! Do you have questions about waterfalls, erosion, or anything else? Have a grown-up help you leave a comment, or send us an email at email@example.com. We'll see you next time, here at the fort!