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Pro:Last time, we started to talk about the glaciers,
教授:上次我们谈到了冰川，
and how these masses less forms from crystallized snow, and some of you were amazed at how huge some of the these glaciers are.
以及大型的冰川如何从结晶雪形成，而且你们很多人都为一些大型的冰川所震惊。
Now, even though it may be difficult to understand how a huge mass less can move or flow, in another word for it, it's really known that the secret that the glaciers flow, because of gravity.
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，而冰川其实是靠地心力来漂浮的已经不再是一个秘密。
But how they flow, and why they flow needs some explaining.
但是冰川怎样浮动，为什么会浮动却仍然需要解释一下。
Now, the first type of the glaciers flow is called: basal slip.
那么，第一种漂浮的冰川叫做基面滑移。
Basal slip or its sliding as it's often called, basically refers to the slipping or sliding of glacier across bedrock, actually across the 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。
So, this process shouldn't be too hard to imagine.
因此这个过程应该就不难理解了。
What happens is that the ice of the base of the glacier is under gradual depression-the depression coming from the weights of the overlaying ice.
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。
And you probably know that the under pressure, the melting temperature of water as the ice I mean, is reduced.
那么你们可能知道，冰块在压力下熔解温度就会降低。
So, ice at the basis of glacier melts, even though it's below zero degree thaws.
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。
And this results in thin layer of water between the glacier and ground.
这就是地面和冰川之前那层水存在的原因。
This layer of water reduces friction is like a lubricant.
这层水能减少摩擦，就像润滑剂一样。
And it allows the glacier to slat or slip over the bedrock.
这就给冰川在基岩上滑动创造了环境。
Ok, now the next type movement we will talk about is called: deformation.
好的，下一种滑动我们称之为变形。
You already known that the ice brittle, if you heated with hammer, it will shatterly 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。
But ice also plastic, you can change the shapes without breaking.
但是冰同样也有塑料的特性，你无需打碎它也能重新塑形。
If you leave, for example, a bar of ice supported only at one end, they end, they unsupported end will deform under its own way due-kind of flatten out one in to get stored it deformed it.
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，使冰块变得平稳。
Think deformation a very slow oozing.
变形是一种缓慢的过程，
Depending on the stresses on the glacier, the ice crystal was in the re-organized.
取决于冰川的压力，冰晶需要重新组织构架。
And during this re-organization the ice crystal re-allied in a way that allows them to slide pass each other.
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 so the glacier oozes downhill without any ice actually melting.
因此冰川往下坡移动时是没有冰块融化的。
Now, there are a couple of the factors that affects the amounts of deformation that takes place or the speed of the glaciers movement for example.
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。
Deformation is more likely to occur the thicker the ices, because at the gravity of the weight its ice.
比如,由于重力因素，变形更容易发生在厚冰层的区域。
And temperature also plays part here, in that does not moves easily.
而且温度也起到了一定的作用，因为冰川不会轻易的移动。
As the ice that is close to the mounting points, in fact, it is not to different from… the weight oil is, thicker at the lower temperature.
事实上，冰块与增长点很接近，和油不一样，温度越低冰层越厚。
So, if you had a glacier in the slightly warmer region, it will flow faster than the glacier in the 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。
Ok, um… Now, let's touch briefly on extension and compression.
好了。现在我们简单的提及一下拉张与挤压。
You textbook includes this as type as a particular type of glacier movement, but you will see that these are … cause many textbooks that omitted as type of movement as included.
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。
And I might not include right now, if there won't in your textbooks.
既然你们的书上没有涉及，我也就不多讲了。
But, basically, the upper parts of the glacier have less pressure on them.
但是，基本上来讲，就是冰川上层的压力小，
So, they don't deform easily, they tend to be more brittle.
因此它们不会很容易重新塑形，而是很脆，
And crevasses can form in this upper layer of glacier.
那么裂缝就会在此部分产生。
When the glacier comes into contact with bedrock walls or the otherwise under some kinds of stresses, but can deform quickly enough.
当冰川涉及到基岩墙或者承受其它压力的时候，就很容易变形。
So, the ice would expand or constrict, and that can cause be crack to form in the surface of the layer of ice, and that brittle the surface ice moving, is sometimes considered a type of glacier movement depending on which source you can thaw to.
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。
Now, as you probably know, glaciers generally move really slowly.
现在，你们也许已经知道了，冰川一般移动起来很慢。
But sometimes, they experience surges, and during these surges, in some places, they can move its speeds as high as 7000 meters per year.
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。
Now, a speed like that are pretty unusual, 100 of times faster than the regular movement of glaciers, but you can actually see glacier move during these surges, though it is rare.
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，尽管并不常见，你还可以看见冰川的移动。
