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Squeaks and I live right next to a river.
我和吱吱住在河边。
It's fun to watch the water rush past, and sometimes people even go fishing in it!
看着水流匆匆流过的样子很有趣，有时人们也会在河里钓鱼。
Like most of the rivers in the world, it flows down hill, right along the ground.
和世界上大多数河流一样，它从山上流下来，沿着地面流动。
But did you know that some rivers flow right off of cliffs? Just look at this one!
但你知道有些河流是从悬崖上飞流下来的吗？就像这条。
This is a river that's flowing off a cliff, and that's what we call a waterfall.
这条河直接从悬崖上流下来，形成了我们所说的瀑布。
This waterfall is called Angel Falls.
这条瀑布叫安赫尔瀑布。
It's in Venezuela, in South America, and it's the tallest waterfall in the whole world!
它在南美洲的委内瑞拉境内，是世界上最高的瀑布。
It's almost 1000 meters tall. That's taller than the tallest building!
它有近1000米高，比最高的建筑还高。
Waterfalls start off as normal rivers, with lots of water flowing towards one place.
瀑布源头是正常的河流，大量的水朝着一个地方流动。
But then the water in the river comes to a cliff.
但当水流到达悬崖时，
It flows over the side and becomes a waterfall!
它流向一边，形成了瀑布。
In the case of Angel Falls, it becomes a huge waterfall.
以安赫尔瀑布为例，它变成了巨大的瀑布。
But the cliff hasn't always been there. The river actually built the cliff.
但悬崖不是永恒存在的，它其实是由河流塑造的。
No, really! Where there's now a huge cliff?
还真不是。现在是巨大悬崖的地儿以前是什么地方？
That used to just be regular flat ground with the river flowing over it.
它过去是普通的平地，河流在上面流动。
But if you looked underneath this river, you'd find a layer of hard rock, then a layer of soft rock or dirt,
但如果你看河底的话，你会发现一层硬岩石，叠加着一层较软的岩层或沙土，
then another layer of hard rock, over and over again in a pattern!
然后还是一层硬岩层，如此一层层叠加起来。
It looks almost like a cake with lots of layers!
就像多层蛋糕。
Some of the parts of the river hit only the hard layers, but the water eventually hits some of the soft layers.
一部分水流只冲刷硬岩层，但最终水都会冲刷软岩层。
That's where the water can do some real work.
在那里，水会起到真正的作用
When water goes over rocks, it can wear away at those rocks over time. We call this erosion.
水对岩石长年累月地进行磨蚀。我们称这个过程叫做侵蚀。
It's easier for the water to erode soft things than hard things,
水磨蚀松软的部分比磨蚀坚硬的部分更容易，
like how it's easy for you to smash a sand castle, but harder for you to break a brick.
就像你能轻易地毁掉一个沙堡，却不容易打碎一块砖。
So, as the water goes over the hard rock, it doesn't do too much.
所以，水流冲刷硬岩层时，起不了多大作用。
But as it goes over the soft rock, it wears away the layer of soft rock more quickly.
但当它冲刷软岩层时，它能更快地磨蚀掉软岩层。
The water takes a few little pieces of rock away, and then a few more, and more, until finally, the soft rock layer is gone.
水一点儿一点儿的磨蚀着岩层，软岩层被磨得越来越多，最终消失了。
When the layer of soft rock is completely eroded away, that creates a cliff between two of the layers of hard rock.
软岩层完全消失了之后，在两层硬岩层之间就形成了悬崖。
This takes a very, very long time to happen, sometimes millions of years.
这个过程非常漫长，有时要经过数百万年的时间。
Exactly! The water flows over the top of the cliff and falls straight down as a waterfall.
你说得对！水流经过悬崖顶部直落而下形成了瀑布。
Angel Falls has grown especially tall because of how the water and the rock interact.
安赫尔瀑布之所以这么高，是水流和岩石的共同作用。
The land around Angel Falls has layers of very soft rock that erode super easily,
安赫尔瀑布周围的土地岩层非常软，很容易被侵蚀，
and tons of incredibly hard rock that hardly erodes at all.
但许多非常坚硬的岩石几乎不受侵蚀。
Because of the big difference in how these layers erode,
因为岩层侵蚀的巨大差异，
this river has carved a huge amount of soft rock out of the way, and very little hard rock.
所以这条河侵蚀掉了大量的软岩层和丁点儿的硬岩层，
That created the tallest waterfall in the whole world!
这就创造出了世界上最高的瀑布！
Thanks for joining us on SciShow Kids!
感谢您收看儿童科学秀！
Do you have questions about waterfalls, erosion, or anything else?
如果你对瀑布、侵蚀或其他有任何疑问，
Have a grown-up help you leave a comment, or send us an email at kids@scishow.com.
让大人帮忙在下方留言，或发邮件至kids@scishow.com。
Thanks, we'll see you next time, here at the fort!
感谢您的收看，我们下期见。沃斯堡等你哦！
