2012年04月14日北美考试机经

Glacial Lakes

Throughout the earth’s history the climate has fluctuated and at times the temperatures have been cooler than they are now. This change in temperature can last somewhere between 2 to 10 million years and is referred to as an ice age. There have been at least five major ice ages in the past one billion years, the most recent of which, the Pleistocene Ice Age, began about 2 million years ago. Glaciers did not continually cover the earth during this time; there have been interglacial periods where temperatures warm slightly and the glaciers melt and retreat. Repeated advance and retreat of a glacier scours the bedrock, preparing the way for the formation of lakes. By the time glaciers completely melted around 10,000 years ago, numerous glacial lakes were formed when the water from melted glaciers fill the hole or space formerly created.

【重点词汇】

1.         Fluctuated: sth ~, it changes a lot in an irregular way, 波动；派生n. fluctuation

2.         Be referred to as：被称为

3.         Pleistocene Ice Age：['plaistəusi:n]， from two million to 11 thousand years ago; extensive glaciations of the northern hemisphere; the time of human evolution; 更新世冰河时期

4.         Glacier：an extremely large mass of ice which moves very slowly, often down a mountain valley, 冰川

5.         Interglacial periods：【地质】间冰河时期

6.         Retreat：v. pull back or move away, or backward, 消退

7.         Score：v. make small marks into the surface of, 在…留下记号

8.         Bedrock：the solid rock in the ground which supports all the soil above it, 基岩

【段落主题】

temperature fluctuates; Pleistocene Ice Age; glaciers melt and retreat; glacial lacks were formed; 

It was at the end of this last Ice Age that a finger of the Cordilleran ice sheet（科迪勒拉冰盖） crept southward into the Idaho panhandle（爱达荷走廊）, forming a large ice dam that blocked the mouth of the Clark Fork River, creating a massive lake 2000 feet deep and containing more than 500 cubic miles of water. Glacial Lake Missoula stretched eastward for some 200 miles and contained more water than Lake Erie(伊利湖) and Lake Ontario(安大略湖) combined.

【重点词汇】

1.         Creep: sth~ somewhere, it moves very slowly, 渐渐蔓延

2.         Ice dam：【水文学】冰坝

3.         Massive：very large in size, quantity or extent. 尺寸/数量/规模非常大的

4.         Stretch：something ~ over an area or distance covers or exists in the whole of that are or distance, 延伸

【段落主题】

…crept southward into…; … stretched eastward for …; form a large ice dam;

Periodically, the ice dam would fail and bring about catastrophic consequences. A large flood of ice-filled and dirt-filled water would burst through the dam, shooting out at a rate 10 times the combined flow of all the rivers of the world. This towering mass of water and ice literally shook the ground as it thundered toward the Pacific Ocean, stripping away hundreds of feet of soil and cutting deep canyons into the underlying bedrock. With flood speeds approaching 65 miles per hour, the lake would have drained in as little as 48 hours.

【重点词汇】

1.         Fail: become gradually weaker or less effective, 衰退

2.         Catastrophic：sth causes a sudden terrible disaster, 灾难性的

3.         A large flood of：a large number of sth, 一大批

4.         Towering：sth is very tall and therefore impressive, 高耸的（文学性）

5.         Literally：to emphasize that what you are saying is true, even though it seems exaggerated or surprising, 确实地

6.         Strip：v. to remove everything that covers it, 剥离

7.         Canyon：a long, narrow valley with very steep sides, 峡谷

【段落主题】

Periodically, the ice dam would fail and bring about catastrophic consequences.

Over time the Cordilleran ice sheet continued moving south and blocked the Clark Fork River again and again, recreating Glacial Lake Missoula（密苏拉）. Over approximately 2,500 years, the lake, ice dam and flooding sequence was repeated dozens of times, leaving a lasting mark on the landscape. Grand Coulee（大谷力峡谷）, Dry Falls（干瀑布）, Palouse Falls（帕劳瑟瀑布） were all created by these flood waters, as were the Missoula and Spokane ground-water resources, numerous wetlands and the fertile Willamette Valley【威拉梅特谷（美国西部俄勒冈州）】 and Quincy Basin.（昆西盆地）

【重点词汇】

1.         Lasting: to describe a situation, result or agreement that continues to exist or have an effect for a very long date 持久的

2.         Wetland: 湿地

3.         Dry Falls：位于美国华盛顿州，距西雅图三小时车程，是现存世界上最大瀑布的遗址。

【段落主题】

Recreate; leave a lasting mark on the landscape; …all created by flood waters…

Among the most varied features left by glaciers are ice-contact deposits due to continental glaciations(大陆冰川). These landforms develop along the margin or outwash of the glacier, leaving behind ice deposits. Glacial outwash is generated when streams of melt water flow away from the glacier and deposit sediment to form broad outwash plains called sandurs.（冰水沉积平原）

【重点词汇】

1.         Deposits: an amount of a substance that has been left somewhere as a result of a chemical or geological process, 沉积物，矿床；（deposit sediment）

2.         Landform：any natural feature of the Earth’s surface, such as a hill, a lake or a beach, 地形，地貌

3.         Margin：the ~ of a place or area is the extreme edge of it, 边缘

4.         Outwash：a mass of gravel, sand, etc, carried and deposited by the water derived from melting glaciers, 【地质】冰水沉积，消融，冲蚀

【段落主题】

     Ice-contact deposits due to continental glaciations; to form broad outwash plains;

The floods caused by receding glaciers or the sudden drainage of an ice-dammed lake often rapidly deposit large quantities of sediment onto the sandur surface. During this process, kettle holes are often formed by the melting of a detached mass of glacial ice that has broken off a glacier and became wholly or partly buried, leaving a depression in a glacial outwash drift. In most cases, kettle holes eventually will fill with water from surface or underground rivers or streams and becomes kettle lakes.

【重点词汇】

1.         Recede: sth becomes weaker, smaller or less intense, 减弱

2.         Drainage：the system or process by which water or other liquids are drained from a place, 排水，排水系统

3.         Kettle holes：【地质学】锅穴

4.         Detached：no longer connected or joined, 独立的

5.         Depression：an area which is lower than the parts surrounding, 洼地

6.         Outwash drift：【地质学】冰水漂积

7.         Kettle lake：锅状湖

【段落主题】

Kettle holes/lakes formed due to sediment onto the sandur surface

Generally speaking, kettle lakes are the result of continental glaciations and are found in northern areas of North America and Europe. In contrast to this kind of lake, alpine(高山的，阿尔卑斯山的) glacial lakes, including paternoster lakes and tarns, are formed by alpine glaciations and are mostly found in mountainous areas. Paternoster lakes are a chain of lakes that may develop in a valley with glacial steps, often each step having a lake. They are so named because of their resemblance with the beads on a rosary. Examples of paternoster lakes occur in the Sierra Nevada Mountains(内华达山脉)  in California and Glacier National Park（国家冰川公园） in Montana. A tarn is a lake that forms when water along with additional snowmelt seep down into the depression of a cirque, the bowl or amphitheater-shaped valley head characteristic of all alpine glacial landforms. The head and sidewalls of a cirque may be nearly vertical, while the floor is often carved into a shallow basin. Excellent examples of tarns lakes are found in North Cascades and Rocky Mountain National Parks.

【重点词汇】

Paternoster lakes: 【水文学】串珠湖,念珠湖

Tarns: 【地理】【水文】 冰斗湖，山中小湖

Resemblance：similarity in appearance or external or superficial details, 相似之处

Bead：a small drop of liquid, 水滴

Seep：pass gradually or leak through or as if through small openings, 渗透

Cirque： a steep-walled semicircular basin in a mountain, may contain a lake, 冰坑/盆地谷

Amphitheater-shaped： 圆形冰斗

【段落主题】

Alpine glacial lakes: paternoster lakes and tarns;