Narrator: Listen to part of a lecture in a geology class.

旁白：请听一段地质学课堂上的讲座部分内容。

Professor: Okay, before we begin, I want to remind you that our field trip to Bryce Canyon National Park is this weekend.

教授：在我们开始之前，我想提醒大家我们的实地考察将于本周末前往布莱斯峡谷国家公园。

Remember the bus leaves early, 5 am, so don't forget to set your alarm clocks.

记住，巴士很早出发，早上5点，请不要忘记设置闹钟。

I think you're all gonna enjoy getting out of the classroom and actually seeing some remarkable geologic phenomena.

我认为你们都会喜欢离开教室并实际看到一些非凡的地质现象。

Now, while we're there, I want you to pay particular attention to two things.

在那里时，我希望你们特别注意两件事情。

One obviously will be the sediment layers making up the rocks since we've spent so much time on sedimentary rocks.

显然，其中一件是我们花费了大量时间研究的沉积岩层。

Bryce Canyon is a great place to see how millions of years have turned layers and layers of tightly packed sediment, mud particles, sand, remains of plants and animals into rock.

布莱斯峡谷是一个很好的地方，可以看到数百万年的沉积物、泥粒、沙子、动植物遗骸如何紧密堆积并变成岩石。

But you're also gonna see some fascinating rock shapes, formations that are the result of the weathering and the erosion processes that occur at Bryce Canyon.

同时，你还会看到一些引人入胜的岩石形状，这些形态是布莱斯峡谷发生的风化和侵蚀过程的结果。

There are two main processes that are important.

这里有两个主要的过程很重要。

The first one is a weathering process called frost wedging.

第一个是称为冰楔作用的风化过程。

Frost wedging is a process that widens cracks in rocks in the wintertime.

在冬季扩大了岩石中的裂缝。

It begins with warm air or daytime sun melting the snow.As the snow turns into water, it seeps into the cracks that occur naturally in sedimentary rocks.

冰楔作用始于白天温暖的空气或太阳融化积雪。当雪变成水时，它会渗入沉积岩中自然形成的裂缝。

At night, this water freezes in the cracks, but when water freezes, it expands quite a bit, which means that it prizes cracks open, gradually, making them wider and breaking off little bits in the process.

夜间，这些水分在裂缝中冻结，但水结冰时体积会膨胀很多，这意味着它逐渐使裂缝变宽，并在此过程中剥落小块岩石。

Now, this thaw-freeze cycle can happen as many as 200 times in a single year.

这种冻融循环一年内可能发生多达200次。

So that makes it the most important weathering process at Bryce Canyon.

因此，这使得冰楔作用成为布莱斯峡谷最重要的风化过程。

The other key process is runoff, which is an erosion process.

另一个关键过程是径流，这是一种侵蚀过程。

Runoff takes place in the summer. The parks in the deserts set the ground very dry.

径流在夏季发生，沙漠地区的地面非常干燥。

When it rains in late summer, the ground is too hard to absorb the water, so it runs off.

当夏末降雨时，地面太硬无法吸收水分，因此水流走。

And as it runs off, it carries away the gravel, the broken bits of rock created by frost wedging in the winter.

当径流发生时，会带走由冬季冰楔作用产生的碎石和小块岩石。

So runoff is the main erosion process that alters the rock landscape in the park.

因此，径流是改变公园内岩石景观的主要侵蚀过程。

And because these processes have occurred over thousands of years, some of the results can be pretty dramatic, like the giant corridors or passage ways that have developed within the rocks.

由于这些过程已经持续了几千年，一些结果可能相当惊人，比如在岩石中发展出的巨大走廊或通道。

These passage ways are known as slot canyons.

这些通道被称为狭缝峡谷。

Here's an example of one, not from the part we're going to. This one is actually in Australia, but the scale is typical.

这里有一个例子，不是我们要去的地方的照片，这张照片实际上来自澳大利亚，但规模典型。

So these huge spaces started out as small cracks throughout the sedimentary rock, then thanks to millions of cycles of frost wedging and runoff, What used to be one big area of rock is now sort of two smaller areas of rock with a corridor in between.

所以这些巨大的空间最初是沉积岩中的小裂缝，然后经过数百万次的冰楔作用和径流，原本是一大片岩石现在变成了两个较小的部分，中间有一条走廊。

We'll have a chance to walk through some like this. These slot canyons are great places to explore.

我们有机会穿过一些像这样的峡谷。这些狭缝峡谷是探索的好地方。

but let me just say, for any of you who aren't from around here, if you ever go on your own, make sure you check a weather forecast first.

不过，让我先说一句，对于那些不熟悉这里的人来说，如果你独自前往，请务必查看天气预报。

A sudden heavy rain can cause a flash flood in a slot canyon. So you want to know when it's safe to explore them.

狭缝峡谷中突然的大雨可能导致山洪暴发。所以你需要知道什么时候进入它们是安全的。

Fortunately, it'll be dry this weekend.

幸运的是，这个周末将会是晴天。

Now, these deep, narrow slots are pretty common. You might even have two of them very close to each other with only a thin wall of rock in between.

现在，这些深而窄的狭缝非常普遍。你甚至可能发现它们非常接近彼此，只有薄薄的一堵岩石墙隔开。

Of course, frost wedging is still at work, so it starts wearing away at the front of the thin wall until you get a hole.

当然，冰楔作用仍在起作用，它开始侵蚀这块薄墙的前面，直到形成一个洞。

I mean, a hole all the way through the wall, front to back. And this hole gets bigger and bigger. Once it's at least one meter in diameter, it's called a window.

我的意思是，从前到后整个穿过的洞。这个洞变得越来越大。一旦它的直径至少达到一米，就被称作窗户。

And eventually, the weight on top of it is just too much.So the roof caves in and only the sides, sometimes it's just one side, is left standing.

最终，顶部的重量太大，屋顶就会坍塌，只剩下侧面，有时只留下一侧站立。

These sides, which look a lot like columns now, are called hoodoos.Here's a photo of something we'll be seeing.

这些侧面看起来像是柱子，被称为石林。这是我们将会看到的一个景象的照片。

One of the things that makes Bryce Canyon unique is that it has more hoodoos than anywhere else in the world. Yes, Margo?

布莱斯峡谷独特之处之一就是它拥有世界上最多的石林。玛戈？

Student: Why is it so lumpy looking?You'd think it would be smoother.

学生：为什么它看起来那么粗糙？我以为它应该更平滑。

Professor: Well, remember, these are sedimentary rocks, so they have layers. Some layers are mostly limestone, and limestone erodes pretty quickly in the presence of any kind of acid.

教授：记住，这些都是沉积岩，所以它们有层理。有些层主要是石灰岩，而且在酸的作用下，石灰岩很容易被侵蚀。

Now, Bryce Canyon is in a very unpolluted area, but even there, the rainwater has a little carbonic acid in it, which causes the limestone to erode.

布莱斯峡谷位于一个非常未受污染的地区，但即使在那里，雨水也含有少量碳酸，这会导致石灰岩被侵蚀。

But other layers are made up of different types of sediment, which aren't so vulnerable to acid, so they don't erode as quickly.

但是其他层由不同的沉积物组成，对酸的抵抗力更强，因此不会那么容易被侵蚀。