托福 TPO 听力笔记（六）：Lecture 4
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：Lecture 4”
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Geology
Last time, we started to talk about the glaciers, and how these masses less
forms from crystallized snow, and some of you were amazed at how huge
some of the these glaciers are. 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. But how
they flow, and why they flow needs some explaining. Now, the first type of the
glaciers flow is called: basal slip.
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. So, this process shouldn’t be too hard to imagine. (13)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. And you
probably know that the under pressure, the melting temperature of water as
the ice I mean, is reduced. So, ice at the basis of glacier melts, even though it’s
below zero degree thaws. And this results in thin layer of water between the
glacier and ground. This layer of water reduces friction is... is like a lubricant.
And it allows the glacier to slat or slip over the bedrock.
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Ok, now the next type movement we will talk about is called: deformation. You
already known that the ice brittle(易碎的), if you heated with hammer, it will shatterly
glass. But ice also plastic, you can change the shapes without breaking. 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. Think deformation a very slow oozing. Depending
on the stresses on the glacier, the ice crystal was in the re-organized. And
during this re-organization the ice crystal re-allied 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 the factors that affects the
amounts of deformation that takes place or the speed of the glaciers
movement for example. Deformation is more likely to occur the thicker the ices,
because at the gravity of the weight its ice. (14.D)And temperature also plays part
here, in that XX does not moves easily. As the ice that is close to the mounting
points,(14.A)in fact, it is not to different from… the weight oil is, thicker at the lower
temperature. So, if you had a glacier in the slightly warmer region, it will flow
faster than the glacier in the cooler region.
Ok, um… Now, let’s touch briefly on extension and compression. 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. And I might not include right now, if there won’t in your textbooks. But,
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basically, the upper parts of the glacier have less pressure on them. So, they
don’t deform easily, they tend to be more brittle. And crevasses can form in this
upper layer of glacier. When the glacier comes into contact with bedrock walls
or the otherwise under some kinds of stresses, but can deform quickly enough.
So, the ice would expand or constrict, and that can cause XXX 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. Now, as you probably know, glaciers generally move really
slowly. (15)But sometimes, they experience surges, and during these surges, in
some places, they can move its speeds as high as 7000 meters per year. 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.
12. What is the lecture mainly about?
� Explanations of how glaciers move
� Landscape changes caused by glacial movement
� Climate changes that influence glacial movement
� Causes of glacial formation
13. 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(排序题)
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Answer choices
A. Friction between the glacier and bedrock is reduced.
B. A liquid layer forms at the base of the glacier.
C. The glacier begins to slide
D. Pressure is increased on the ice
答案：CBDA
14. What factors are involved in the amount of deformation(变形) a glacier undergoes?
Click on 2 answers
� The thickness of glacial ice
� The hardness of glacial ice
� The amount of water beneath the glacial ice
� The temperature of the glacial ice
15. What does the professor say about the speed of glaciers?
� It affects the amount of glacial ice that forms
� It can be fast enough for movement to be noticeable
� It is reduced by cracks in the ice
� It is unusually high in colder regions
16. what does the professor explain when he says this()
� A characteristic of ice that is related to glacial movement
� How scientists first discovered that glaciers could move
� That factors like temperature can affect the strength of ice
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� Why deformation is the most common type of glacial movement
17. What does the professor imply about compression and extension?
� He believes it accounts for a great deal of glacial movement
� He thinks it is a slower type of a glacial movement than basal slip
� He is not convinced that it is a type of glacial movement
� He does not agree that it causes fissures in glaciers.
来源：小马过河
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