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第1段

1 .<-NARRATOR:->Listen to part of a lecture in a geology class.

旁白:听一段关于地理学的讲座。

第2段

1 .<-MALE PROFESSOR:->Last time we started to talk about glaciers and how these masses of ice form from crystallized snow.

教授:上次我们谈论了冰川,以及这些大块的冰是如何从结晶雪形成的。

2 .And some of you were amazed at how huge some of these glaciers are.

很多学生都为一些大型的冰川所震惊。

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

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

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

但是冰川怎样浮动,浮动的方式仍然需要解释一下。

第3段

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

那么,第一种类型的冰川浮动叫做基面滑移。

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

基面滑移,或者也被称作底部滑动,其实就是指冰川横穿基岩的滑动,实际上应该是在基岩顶部的一层薄薄的水上滑动。

3 .Um, so, this process shouldn't be too hard to imagine. What happens is that the ice of the base of glacier is under a great deal of pressure, the pressure coming from the weight of the overlying ice.

因此这个过程应该就不难想象了。实际上就是冰川底部的冰承受着巨大的压力,压力来自于覆盖在冰面上的冰的重量。

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

你们可能知道,冰块在压力下融化温度就会降低。

5 .So ice at the base of the glacier melts, even though it’s below zero degrees Celsius, and this results in a thin layer of water between the glacier and the ground.

所以说,冰川底部的冰块就会融化,即便它还是在摄氏零度以下,这导致了冰川和地面之间存在一层薄薄的水。

6 .This layer of water reduces friction, it’s, it’s like a lubricant, and it allows the glacier to slide or slip over the bedrock. OK?

这层水能减少摩擦,就像...就像润滑剂一样,它允许冰川划过基岩,知道了么?

第4段

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

下面一种类型的滑动我们称之为变形。

2 .You already know that ice is brittle—if you hit it with a hammer, it will shatter like glass.

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。

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

但是冰同样可塑的,你无需打碎它也能重新塑形。

4 .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.

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在自身的重量下变形,它会在另一端使冰块变得平稳。

5 .Think of deformation as a very slow oozing.Depending on the stresses on the glacier, the ice crystal within it reorganize.

把变形想象成一个非常缓慢的渗出。根据冰川的压力,内部的冰晶会重组。

6 .And during this reorganization, the ice crystals realign in a way that allows them to slide pass each other.

在此重组过程中,冰晶会以一种允许它们相互滑动的方式重新排列。

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

因此,冰川在没有任何融化的情况下向下延伸。

第5段

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

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。

2 .For example, deformation is more likely to occur the thicker the ice is—because of the gravity of the weight of the ice.

比如,由于重力因素,变形更容易发生在厚冰层的区域。

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

而且温度也起到了一定的作用,冰川的移动并不像靠近融点的冰那么容易。

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

事实上,它和石油方式没有太大的区别,温度越底冰层越厚。

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

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。

第6段

1 .OK, um, now I'd like to touch briefly on extension and compression.

好了。现在我们简单的提及一下拉张与挤压。

2 .Your textbook includes this as types—as a particular type—of glacier movement.

你们的教科书上把这种类型列为冰川移动的特殊类型。

3 .But you'll see that there are as many textbooks that omitted it as a type of movement as include it.

但是你们会看见……许多教科书把这部分省略掉了,和一种类型的运动包括它一样。

4 .And I might not include it right now if it weren't in your textbook.

如果不是在你们的课本里,我就不会讲了。

5 .But um, basically, the upper parts of glaciers have less pressure on them, so they don’t deform as easily, they tend to be more brittle.

但是,基本上来讲,就是冰川上层的压力小,因此它们不会很容易重新塑形,而是很脆。

6 .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.

裂缝会在冰川的上层形成,当冰川接触到基岩墙或者在某种压力下,但不能很快地变形时。

7 .So the ice would expand or constrict, and that can cause big fissures, big cracks to form in the surface layers of the ice.

因此,生成裂缝的冰就会拉张或挤压,这就导致在冰的表层形成巨大的裂缝。

8 .And that brittle surface ice moving,is sometimes considered a type of glacier movement,depending on which source you are consulting.

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,有时候不被看做是冰川的移动类型,取决于你咨询的来源。

第7段

1 .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 7,000 meters per year.

现在,虽然你们知道了,冰川一般移动起来很慢。但是有时候,它们也会移动很快,它们会经历突进,在突进过程中,有些地方的冰川移动速度甚至可以达到每年7000 米。

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

那么这种速度往往是不寻常的,是冰川常规移动速度的数百倍,但是你可以看见冰川在突进过程中的移动,尽管并不常见。