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  • 冰川的侵蚀和沉积

    Lesson Objectives
    ::经验教训目标

    • Describe how continental and valley glaciers form.
      ::描述大陆和河谷冰川是如何形成的。
    • Explain how glaciers cause erosion.
      ::解释冰川如何导致侵蚀。
    • Identify landforms deposited by glaciers.
      ::确定冰川沉积的地形形态。

    Lesson Vocabulary
    ::词汇表课程

    • continental glacier
      ::大陆冰川
    • glacial till
      ::冰川至
    • glacier
      ::冰川冰川
    • moraine
      ::闪光光
    • plucking
      ::采采
    • valley glacier
      ::河谷冰川

    Introduction
    ::导言

    Imagine you are standing in a farm field in central Illinois. The land is so flat you can see for miles and miles. On a clear day, you might see a grain silo 20 miles away. You might think to yourself, it sure is flat around here. If you drive one hundred miles to the south, the landscape changes. In southern Illinois, there are rolling hills. Why do you think this is? What could have caused these features? There are no big rivers that may have eroded and deposited this material. The ground is capable of supporting grass and trees, so wind erosion would not explain it. To answer the question, you need to go back 12,000 years. 
    ::想象一下你站在伊利诺伊州中部的农场里。 这片土地是平坦的, 你可以看到数英里和数英里。 在一个晴朗的日子里, 你可能会看到一个离地球20英里的粮仓。 你可能会想到这里是平坦的。 如果你把100英里开到南边, 地貌就会变化。 在伊利诺伊州南部, 为什么会有滚动的山丘? 为什么会这样呢? 是什么原因导致这些特征? 没有大河可能侵蚀和沉没了这些物质。 地面能够支撑草和树木, 因此风蚀无法解释它。 要回答这个问题, 您需要追溯12000年。

    Around 12,000 years ago, a giant ice sheet covered much of the midwest United States. Springfield, Illinois, was covered by over a mile of ice. It's hard to imagine a mile thick sheet of ice. The massive ice sheet, called a glacier, caused the features on the land you see today. Where did glaciers go? Where can you see them today? 
    ::大约12000年前,一个巨大的冰盖覆盖了美国中西部的大部分地区。伊利诺伊州斯普林菲尔德(Springfield)覆盖了一英里长的冰层。很难想象一英里厚的冰层。巨大的冰层被称为冰川,造成了今天你所看到的这片土地上的特征。冰川去了哪里?今天你在哪里看到它们呢?

    Glaciers  are masses of flowing ice. Today, they cover only about 10 percent of Earth's surface. They are getting smaller and smaller. As the Earth's temperatures have risen, the glaciers retreated. About 12,000 years ago, much of Europe was also covered with glaciers.
    ::冰川是流动冰块的团团。 如今,冰川只覆盖地球表面的10%左右。 它们越来越小。 随着地球温度的上升,冰川开始消退。大约12000年前,欧洲大部分地区也覆盖着冰川。

    Glaciers erode large areas of land. They leave behind features on the surface. These landforms are like clues. They show the direction a glacier flowed. They also tell scientists how far they advanced. Did glaciers leave clues where you live? Would you know what to look for?
    ::冰川侵蚀了大片土地,在地表上留下一些地貌。这些地貌就像线索。它们显示了冰川流动的方向。它们还告诉科学家它们前进了多远。冰川留下的线索是你住的地方吗?你知道要寻找什么吗?

    How Glaciers Form
    ::冰川的形态

    You may be wondering, how can a glacier get so big? Why does it move? These are both good questions. 
    ::你也许在想,冰川怎么会这么大?为什么移动?这两个问题都很好。

    In the winter months, precipitation falls as snow. This solid form of water builds up on the ground as long as the temperatures stay cold enough. As the temperature rises, the snow starts to melt. The frozen water changes state back into a liquid state. Nearer the poles, summer does not last very long. If the summer is long enough and warm enough, all the snow may melt. This is what typically happens now. The earth was a little cooler 12,000 years ago. As a result, during the summer months, that amount of snow did not melt. It may have only been an inch or so of snow that melted. The following winter, snow fell on top of this left-over snow. This next winter's snowfall had a head start. Year after year, the snow that did not melt became thicker and thicker. Inch by inch the snow started to build up. Over many years, layer upon layer of snow compacted and turned to ice. As this ice grew thicker and thicker, it began to spread out. Gravity was pulling it down, so it had no place to go but out. This spreading out at the bottom of the ice sheet is what caused the glaciers to "move," or advance. Starting near the poles, the glaciers were forced southward in all directions. 
    ::冬季, 降水会降为雪。 只要温度足够寒冷, 这种坚固的水形式就会在地面上积聚。 随着温度升高, 雪开始融化。 冷冻的水会将状态变回液态。 更接近极点, 夏天不会持续很久。 如果夏天足够长, 温度足够暖和, 所有的雪都会融化。 这是现在通常发生的情况。 12 000年前, 地球是略微冷一点的 。 因此, 在夏季几个月里, 积雪的数量并没有融化 。 它可能只是雪融化的一寸或几寸雪。 过冬后, 雪会降在雪的顶端。 明年冬天的雪会有一个头部开始。 年复一年, 没有融化的雪会变厚, 夏天的雪会融化。 积雪开始积雪开始累积。 多年来, 积雪层层层层层的层层层层变厚, 开始膨胀, 它开始膨胀。 由于冰层变厚, 冰雪层开始向外拉下, 它没有地方, 但它没有地方, 但它没有地方, 但它会消失。

    There are two different types of glaciers. Continental glaciers are the type that is described above.  There are also valley glaciers. Instead of forming at the far northern or southern reaches of the Earth, they form in cold mountain regions. Each type forms some unique features. These features are caused by erosion and deposition of material. An example of each type is pictured in  Figure   .
    ::冰川有两种不同类型:大陆冰川是上述类型的冰川;还有河谷冰川;冰川不是在地球最北端或最南端形成,而是形成于寒冷的山区;每一种冰川都有独特的特征;这些特征是由物质侵蚀和沉积造成的;每一种冰川的例子见图一。

    • A  continental glacier  is spread out over a huge area. It may cover most of a continent. Today, continental glaciers cover most of Greenland and Antarctica. In the past, they were much larger.
      ::大陆冰川分布在巨大的地区,可能覆盖大部分大陆,如今,大陆冰川覆盖了大部分格陵兰和南极洲,过去大得多。
    • A  valley glacier  is long and narrow. Valley glaciers form in mountains. They flow downhill through mountain river valleys.
      ::山谷冰川是漫长而狭窄的, 山谷冰川在山中形成, 山中下坡流过山河谷。

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    (A) The continent of Antarctica is covered with a continental glacier. (B) A valley glacier in the Canadian Rockies. (C) The surface of a valley glacier.
    :sadA) 南极洲大陆覆盖大陆冰川。 (B) 加拿大落基山脉的河谷冰川。 (C) 河谷冰川表面。

    Erosion by Glaciers
    ::冰川侵蚀

    Like flowing water, flowing ice erodes the land. It also can deposit the material elsewhere. Glaciers cause erosion in two main ways: plucking and abrasion.
    ::像流水一样,流冰侵蚀土地,也可以将物质存放在别处。 冰川以两种主要方式造成侵蚀:采掘和磨损。

    • Plucking  is caused when sediments are picked up by a glacier. They freeze to the bottom of the glacier and are carried away by the flowing ice.
      ::当沉积物被冰川收集起来时,便会造成鼠潮,它们冻到冰川底部,被流动的冰块冲走。
    • Abrasion occurs when glaciers scrape over the Earth's surface. The ice sheet acts like sandpaper. The ice contains sediments and rocks frozen in the ice. The rocks and sediment grind away as the glacier moves. They wear away rock. They may also leave scratches and grooves in them. Scientists use these grooves to learn about the direction the glacier has moved.
      ::当冰川刮过地球表面时,就会出现磨损。冰盖就像砂纸一样。冰层中含有冰层中的沉积物和岩石。冰层中含有冰层中的沉积物和岩石。随着冰川的移动,岩石和沉积物会碎裂。它们会耗尽岩石。它们也会留下划痕和沟槽。科学家们利用这些槽子来了解冰川移动的方向。

    Erosion by Valley Glaciers
    ::山谷冰川侵蚀

    Just like continental glaciers, valley glaciers leave clues. Even 12,000 years later, evidence of valley glaciers can be seen on the landscape. One such feature is the presence of a U-shaped valley. 
    ::就像大陆冰川一样,河谷冰川留下线索。 即使在12 000年后,在地貌上也可以看到河谷冰川的证据。 其中一个特征就是存在一个U形的河谷。

    • Glaciers on mountains flow down river valleys. Fast moving mountain streams carve deep V-shaped valleys. Valley glaciers partially fill the valley. The rock and sediment they pick up scrape on the sides of the valley. The scraping causes the sides of the valley to be eroded. Glaciers carve out a U-shaped valley. 
      ::山上的冰川流向河谷。快速移动的山流将深处的V形山谷切成碎片。峡谷的冰川部分填满了河谷。冰川和沉积物在河谷的两侧刮起刮痕。刮痕使河谷的两侧受到侵蚀。冰川从一个U形山谷中划出一个U形山谷。

    Deposition by Glaciers
    ::冰川沉积

    While glaciers erode the landscape, they also deposit materials. Glaciers deposit their sediment when they melt. They drop and leave behind whatever was once frozen in their ice. It's usually a mixture of particles and rocks. It can be of all sizes, called  glacial till . Water from the melting ice may form lakes or other water features.  Figure    shows some of the landforms. 
    ::当冰川侵蚀地貌时,它们也会沉积物质。冰川在融化时会沉积在沉积中。 它们会落下并留下曾经被冰冻过的东西。 它通常由粒子和岩石混合而成。 它可能具有各种大小, 被称为冰川, 融化后的冰水可能形成湖泊或其他水体特征。 图显示一些陆地形态 。

    • Moraine  is sediment deposited by a glacier. A ground moraine is a thick layer of sediments left behind by a retreating glacier. An end moraine is a low ridge of sediments deposited at the end of the glacier. It marks the greatest distance the glacier advanced. 
      ::甲状腺是冰川沉积的沉积物,地面是冰川退缩留下的厚厚的沉积物层,末面是冰川末端沉积的低沉积物脊,是冰川前方最远的冰川。
    • A drumlin is a long, low hill of sediments deposited by a glacier. Drumlins often occur in groups. These groups are called drumlin fields. The narrow end of each drumlin points in the direction of an advancing glacier.
      ::鼓林是一个由冰川沉积的长低沉积山丘,鼓林通常以群居形式出现,这些群被称为鼓田,每个鼓林点向前进的冰川方向的狭端。
    • An esker is a winding ridge of sand deposited by a stream of meltwater. Such streams flow underneath a retreating glacier.
      ::螺旋桨是融化水流沉积的沙丘,这种流水流在退缩的冰川下流。
    • A kettle lake occurs where a chunk of ice melt as they are left behind as a glacier retreats. When the huge chuck of ice melts it leaves a depression. The meltwater fills it to form a lake.
      ::茶水湖发生于一片冰融化的地方,因为冰在冰川退缩时被抛在后面。当巨大的冰块融化时,它会留下压抑。融水将它填充成湖泊。

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    Take a look at the glacial deposits. How far did the glacier in the diagram advance before it started retreating?
    ::看看冰川的沉积。图中的冰川在开始退缩之前 前进了多远?

    Lesson Summary
    ::经验教训摘要

    • Glaciers are masses of flowing ice.
      ::冰川是流动的冰块
    • Continental glaciers are huge. They may spread out over much of a continent.
      ::大陆冰川是巨大的,它们可能散布在大洲的大部分地区。
    • Valley glaciers are long and narrow. They form in mountains and flow through mountain river valleys.
      ::河谷冰川既长又窄,在山中形成,流经山河谷。
    • Glaciers cause erosion by plucking and abrasion. 
      ::冰川通过采摘和磨损造成侵蚀。
    • Glaciers deposit their sediment when they melt. Landforms deposited by glaciers include drumlins, kettle lakes, and eskers.
      ::冰川在融化时沉积在泥沙中,冰川沉积在地表上,包括鼓林、小溪湖和eskers。

    Lesson Review Questions
    ::经验回顾问题

    Recall
    ::回顾

    1. What is a glacier?
      ::什么是冰川?
    1. Describe how glaciers form.
      ::描述冰川的形成
    1. Identify the two main ways glaciers cause erosion.
      ::确定冰川导致侵蚀的两个主要途径。
    1. Name and describe three unique features eroded by valley glaciers.
      ::名称和描述三个被河谷冰川侵蚀的独特特征。
    1. What is glacial till?
      ::冰雪到底要到哪里去?

    Apply Concepts
    ::应用概念

    1. Create a lesson to teach younger students how a kettle lake forms. Outline your lesson.
      ::创建课程, 向年轻学生传授水壶湖的形态。 概要描述您的教训 。

    Think Critically
    ::仔细仔细思考

    1. Compare and contrast valley and continental glaciers and how they change Earth's surface.
      ::对比和对比山谷和大陆冰川 以及它们如何改变地球表面
    1. Areas once covered by glaciers may have large boulders called erratics, like the one in the photo below. Infer why erratics typically consist of a different type of rock than the bedrock where they are found.
      ::曾经被冰川覆盖的地区可能有大块巨石,称为变异,就像下面照片中的巨石。 推论为什么变异通常由不同类型的岩石组成,而不是发现这些岩石的基岩。

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    Points to Consider
    ::需要考虑的要点

    So far in this chapter, you've read how moving water, air, and ice shape Earth's surface. Water and ice move because of gravity.
    ::到目前为止,在本章中,你读过 水、空气和冰是如何移动的 地球表面。水和冰因重力而移动。

    • Do you think gravity can erode and deposit sediment without the help of water or ice?
      ::你认为引力会侵蚀和沉积沉积物 没有水或冰的帮助?
    • How might gravity alone shape Earth's surface?
      ::光靠引力如何影响地球表面?