評論
打印
Pro:Last time, we started to talk about the glaciers,
教授:上次我們談到了冰川，
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從結晶雪形成，而且你們很多人都為一些大型的冰川所震驚。
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.
現在，即便了解大型冰川如何移動或漂浮這個現象有些困難，而冰川其實是靠地心力來漂浮的已經不再是一個秘密。
But how they flow, and why they flow needs some explaining.
但是冰川怎樣浮動，為什么會浮動卻仍然需要解釋一下。
Now, the first type of the glaciers flow is called: basal slip.
那么，第一種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，或者也被稱作底部滑動，其實就是指冰川在基巖上的滑動，細致來講應該是在基巖上的一層水上滑動的現象。
So, this process shouldn't be too hard to imagine.
因此這個過程應該就不難理解了。
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.
實際上就是冰川底部的冰塊承受來自上方冰塊漸增的重量壓力。
And you probably know that the under pressure, the melting temperature of water as the ice I mean, is reduced.
那么你們可能知道，冰塊在壓力下熔解溫度就會降低。
So, ice at the basis of glacier melts, even though it's below zero degree thaws.
所以說，冰川底部的冰塊就會融化，即便它的溫度還是在零度以下。
And this results in thin layer of water between the glacier and ground.
這就是地面和冰川之前那層水存在的原因。
This layer of water reduces friction is like a lubricant.
這層水能減少摩擦，就像潤滑劑一樣。
And it allows the glacier to slat or slip over the bedrock.
這就給冰川在基巖上滑動創造了環境。
Ok, now the next type movement we will talk about is called: deformation.
好的，下一種滑動我們稱之為變形。
You already known that the ice brittle, if you heated with hammer, it will shatterly glass.
大家都知道冰塊易碎，倘若你拿錘子敲擊，它會立即如玻璃一樣碎裂。
But ice also plastic, you can change the shapes without breaking.
但是冰同樣也有塑料的特性，你無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，如果你放置一塊只有一面支撐的冰，那么未被支撐的這邊冰將會以自己的方式重新塑形，使冰塊變得平穩。
Think deformation a very slow oozing.
變形是一種緩慢的過程，
Depending on the stresses on the glacier, the ice crystal was in the re-organized.
取決于冰川的壓力，冰晶需要重新組織構架。
And during this re-organization the ice crystal re-allied in a way that allows them to slide pass each other.
在此期間，冰晶會在允許它們相互移動的情況下重新聯合在一起。
And so the glacier oozes downhill without any ice actually melting.
因此冰川往下坡移動時是沒有冰塊融化的。
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.
現在說一下影響冰川變形數量及冰川移動速度的幾個因素。
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，變形更容易發生在厚冰層的區域。
And temperature also plays part here, in that does not moves easily.
而且溫度也起到了一定的作用，因為冰川不會輕易的移動。
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.
事實上，冰塊與增長點很接近，和油不一樣，溫度越低冰層越厚。
So, if you had a glacier in the slightly warmer region, it will flow faster than the glacier in the cooler region.
因此，在稍溫暖地帶的冰川，就會比更冰冷地帶的冰川更容易移動。
Ok, um… Now, let's touch briefly on extension and compression.
好了。現在我們簡單的提及一下拉張與擠壓。
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.
你們的教科書上把這種類型列為冰川移動的特殊類型，但是你們會看見…許多教科書把這部分省略掉了，不認為這是一種冰川移動。
And I might not include right now, if there won't in your textbooks.
既然你們的書上沒有涉及，我也就不多講了。
But, basically, the upper parts of the glacier have less pressure on them.
但是，基本上來講，就是冰川上層的壓力小，
So, they don't deform easily, they tend to be more brittle.
因此它們不會很容易重新塑形，而是很脆，
And crevasses can form in this upper layer of glacier.
那么裂縫就會在此部分產生。
When the glacier comes into contact with bedrock walls or the otherwise under some kinds of stresses, but can deform quickly enough.
當冰川涉及到基巖墻或者承受其它壓力的時候，就很容易變形。
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，冰塊就會拉張或擠壓，這就導致冰塊破裂并重新形成表面的冰層，這些易碎的表面冰層的移動有時候就被看做是一種冰川移動，主要還是看融化源在哪里。
Now, as you probably know, glaciers generally move really slowly.
現在，你們也許已經知道了，冰川一般移動起來很慢。
But sometimes, they experience surges, and during these surges, in some places, they can move its speeds as high as 7000 meters per year.
但是有時候，它們也會移動很快，有些地方的冰川移動速度甚至可以達到每年 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.
那么這種速度往往是不尋常的，是一般冰川移動速度的 100 倍，盡管并不常見，你還可以看見冰川的移動。
