『新东方在线托福听力』为托福考生准备了ETS托福TPO/Official 7 Lec 4听力练习：Listen again to part of the Lecture.Then answer the question. What does the professor imply about compression and extension?原文题目答案解析，TPO/Official 7 Lec 4听力原文范文音频翻译。

托福TPO/Official 7 Lec 4听力原文Listen again to part of the Lecture.Then answer the question. What does the professor imply about compression and extension?-新东方托福官方网校手机版

旁白：听一段关于地理学的讲座。

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

教授：上次我们谈论了冰川，以及大型的冰川如何从结晶雪形成而来，很多学生都为一些大型的冰川所震惊。

Pro: Last time, we started to talk about glaciers and how these masses of ice form from crystallized snow, and some of you were amazed at how huge some of these glaciers are.

现在，即便了解大型冰川如何移动或漂浮这个现象有些困难，而这已经不再是一个秘密，冰川其实是靠地心力来漂浮的。

Now, even though it may be difficult to understand how a huge mass of ice can move or flow, it’s another word for it, it’s really known that no secret that the glaciers flow because of gravity.

但是冰川怎样浮动，为什么会浮动却仍然需要解释一下。

But how they flow, the way they flow, needs some explaining.

那么，第一种漂浮的冰川叫做基面滑移。

Now, the first type of glacier flow is called: basal slip.

基面滑移，或者也被称作底部滑动，其实就是指冰川在基岩上的滑动，细致来讲应该是在基岩上的一层水上滑动的现象。

Basal slip or sliding as it’s often called, basically refers to the slipping or sliding of a glacier across bedrock, actually across a thin layer of water on top of the bedrock.

因此这个过程应该就不难理解了。

Um, so, this process shouldn't be too hard to imagine.

实际上就是冰川底部的冰块承受来自上方冰块渐增的重量压力。

What happens is that the ice at the base of the glacier is under a great deal of pressure--the pressure coming from the weight of the overlying ice.

那么你们可能知道，冰块在压力下熔解温度就会降低。

And you probably know that under pressure, the melting temperature of water, of the ice I mean, is reduced.

所以说，冰川底部的冰块就会融化，即便它的温度还是在零度以下。

So, ice at the base of the glacier melts, even though it’s below zero degree celsius.

这就是地面和冰川之前那层水存在的原因。

And this results in a thin layer of water between the glacier and the ground.

这层水能减少摩擦，就像……就像润滑剂一样。

This layer of water reduces friction is... is like a lubricant.

这就给冰川在基岩上滑动创造了环境。好了。

And it allows the glacier to slide or slip over the bedrock. Ok?

下面一种滑动我们称之为变形。

Now the next type of movement we will talk about is called: deformation.

大家都知道冰块易碎，倘若你拿锤子敲击，它会立即如玻璃一样碎裂。

You've already known that ice is brittle, if you hit it with a hammer, it will shatter like glass.

但是冰同样也有塑料的特性，你无需打碎它也能重新塑形。

But ice is also plastic, it can change shape without breaking.

比如，如果你放置一块只有一面支撑的冰，那么未被支撑的这边冰将会以自己的方式重新塑形。

If you leave, for example, a bar of ice supported only at one end, the end, the unsupported end will deform under its own weight.

它最终会变平，发生变形和溶解。

It'll kind of flatten out at one end, get distorted, deformed.

Think of deformation as a very slow oozing.

取决于冰川的压力，冰晶需要重新组织构架。

Depending on the stresses on the glacier, the ice crystals within it reorganize.

在此期间，冰晶会在允许它们相互移动的情况下重新联合在一起。

And during this re-organization the ice crystals realign in a way that allows them to slide pass each other.

因此冰川往下坡移动时是没有冰块融化的。

And so the glacier oozes downhill without any ice actually melting.

现在说一下影响冰川变形数量及冰川移动速度的几个因素。

Now, there are a couple of factors that affect the amount of deformation that takes place or the speed of the glacier’s movement for example.

比如，由于重力因素，变形更容易发生在厚冰层的区域。

Deformation is more likely to occur the thicker the ice is, because of the gravity of the weight of the ice.

因为寒冷的冰川不会像接近融点的冰川那样方便移动。

And temperature also plays a part here, in that cold ice does not move as easily as ice that is close to the melting point.

事实上，冰块与增长点很接近，和油不一样，温度月底冰层越厚。

In fact, it is not too different from... the way oil is, thicker at lower temperatures.

因此，在稍温暖地带的冰川，就会比更冰冷地带的冰川更容易移动。

So, if you have a glacier in a slightly warmer region, it will flow faster than a glacier in a cooler region.

好了。现在我们简单的提及一下拉张与挤压。

Ok, um... Now, I’d like to touch briefly on extension and compression.

你们的教科书上把这种类型列为冰川移动的特殊类型，但是你们会看见……许多教科书把这部分省略掉了，不认为这是一种冰川移动。

Your textbook includes these as types, as a particular type of glacier movement, but you will see that there are... as many textbooks that omit it as a type of movement as include it.

既然你们的书上不会有，我也就不多讲了。

And I might not include it right now, if it weren’t in your textbook.

但是，基本上来讲，就是冰川上层的压力小。

But, basically, the upper parts of glaciers have less pressure on them.

因此它们不会很容易重新塑形，而是很脆。

So, they don’t deform easily, they tend to be more brittle.

And crevasses can form in this upper layers of the glacier.

但是，当冰川触及到基岩墙或者承受其他压力的时候，并不能很快速的变形。

When the glacier comes into contact with bedrock walls or is otherwise under some kind of stress, but can’t deform quickly enough.

因此，冰块就会拉张或挤压，这就导致冰块破裂并重新形成表面的冰层，这些易碎的表面冰层的移动有时候就被看做是一种冰川移动，主要还是看融化源在哪里。

So, the ice would expand or constrict, and that can cause big fissures big cracks to form in the surface layers of the ice, and that brittle surface ice moving is sometimes considered a type of glacier movement depending on which source you are consulting.

现在，你们也许已经知道了，冰川一般移动起来很慢。

Now, as you probably know, glaciers generally move really slowly.

但是有时候，它们也会移动很快，有些地方的冰川移动速度甚至可以达到每年7000米。

But sometimes, they experience surges, and during these surges, in some places, they can move at speeds as high as 7000 meters per year.

那么这种速度往往是不寻常的，是一般冰川移动速度的100倍，你还可以看见冰川的移动，尽管并不常见。

Now, speeds like that are pretty unusual, hundreds of times faster than the regular movement of glaciers, but you can actually see glacier move during these surges, though it is rare.

The professor discusses the process of basal slip. Put the steps in the correct order. Click on a sentence, then drag it to the space where it belongs.

What factors are involved in the amount of deformation a glacier undergoes?

What does the professor say about the speed of glaciers?

What does the professor explain when he says this:

Listen again to part of the Lecture.Then answer the question. What does the professor imply about compression and extension?

Last time, we started to talk about glaciers and how these masses of ice form from crystallized snow, and some of you were amazed at how huge some of these glaciers are. Now, even though it may be difficult to understand how a huge mass of ice can move or flow, it’s another word for it, it’s really known that no secret that the glaciers flow because of gravity. 
But how they flow, the way they flow, needs some explaining. 
Now, the first type of glacier flow is called: basal slip. 
Basal slip or sliding as it’s often called, basically refers to the slipping or sliding of a glacier across bedrock, actually across a thin layer of water on top of the bedrock. So, this process shouldn’t be too hard to imagine. What happens is that the ice at the base of the glacier is under a great deal of pressure—the pressure coming from the weight of the overlying ice. And you probably know that under pressure, the melting temperature of water, of the ice I mean, is reduced. So, ice at the base of the glacier melts, even though it’s below zero degree Celsius. 
And this results in a thin layer of water between the glacier and the ground. This layer of water reduces friction is... is like a lubricant. And it allows the glacier to slide or slip over the bedrock. OK? 
Now the next type of movement we will talk about is called: deformation. You’ve already known that ice is brittle, if you hit it with a hammer, it will shatter like glass. But ice is also plastic, it can change shape without breaking. If you leave, for example, a bar of ice supported only at one end, the end, the unsupported end will deform under its own weight, it’ll kind of flatten out at one end, get distorted, deformed. Think of deformation as a very slow oozing. Depending on the stresses on the glacier, the ice crystal within it reorganize. And during this re-organization the ice crystals realign in a way that allows them to slide pass each other. And so the glacier oozes downhill without any ice actually melting. 
Now, there are a couple of factors that affect the amount of deformation that takes place or the speed of the glacier’s movement. For example, deformation is more likely to occur the thicker the ice is, because of the gravity of the weight of the ice. And temperature also plays a part here, in that cold ice does not move as easily as ice that is close to the melting point, in fact, it is not too different from… the way oil is, thicker at lower temperatures. So, if you have a glacier in a slightly warmer region, it will flow faster than a glacier in a cooler region. 
Ok, um… Now, I’d like to touch briefly on extension and compression. Your textbook includes these as types, as a particular type of glacier movement, but you will see that there are …as many textbooks that omit it as a type of movement as include it. And I might not include it right now, if it weren’t in your textbook. But, basically, the upper parts of glaciers have less pressure on them. So, they don’t deform easily, they tend to be more brittle. And crevasses can form in this upper layers of the glacier. When the glacier comes into contact with bedrock walls or is otherwise under some kind of stress, but can’t deform quickly enough. So, the ice would expand or constrict, and that can cause big fissures big cracks to form in the surface layers of the ice, and that brittle surface ice moving is sometimes considered a type of glacier movement depending on which source you are consulting. 
Now, as you probably know, glaciers generally move really slowly. But sometimes, they experience surges, and during these surges, in some places, they can move at speeds as high as 7000 meters per year. Now, speeds like that are pretty unusual, hundreds of times faster than the regular movement of glaciers, but you can actually see glacier move during these surges, though it is rare.
Now the next type of movement we will talk about is called: deformation. You’ve already known that ice is brittle, if you hit it with a hammer, it will shatter like glass. But ice is also plastic, it can change shape without breaking. If you leave, for example, a bar of ice supported only at one end, the end, the unsupported end will deform under its own weight, it’ll kind of flatten out at one end, get distorted, deformed. Think of deformation as a very slow oozing. Depending on the stresses on the glacier, the ice crystal within it reorganize. And during this re-organization the ice crystals realign in a way that allows them to slide pass each other. And so the glacier oozes downhill without any ice actually melting.
Now, I’d like to touch briefly on extension and compression. Your textbook includes these as types, as a particular type of glacier movement, but you will see that there are …as many textbooks that omit it as a type of movement as include it. And I might not include it right now, if it weren’t in your textbook. But, basically, the upper parts of glaciers have less pressure on them. So, they don’t deform easily, they tend to be more brittle. And crevasses can form in this upper layers of the glacier. When the glacier comes into contact with bedrock walls or is otherwise under some kind of stress, but can’t deform quickly enough. So, the ice would expand or constrict, and that can cause big fissures big cracks to form in the surface layers of the ice, and that brittle surface ice moving is sometimes considered a type of glacier movement depending on which source you are consulting.