54 The Great Lakes-Mid

The Great Lakes FOCUS Question How did the Great Lakes form?

五大湖焦点问题五大湖是如何形成的?

The Largest Lakes In the middle of North America lie five lakes, all connected by rivers. These are no ordinary lakes. They're the Great Lakes. Together they hold over 20 percent of Earth's fresh water. If the Great Lakes were spread out evenly, their waters would flood the continental United States 3 meters (9 ft.) deep! Like small seas, the Great Lakes have waves, powerful currents, and even tiny tides. Where did these enormous lakes come from? The formation of the Great Lakes goes back to the most recent ice age. The lakes, and the land around and under them, reveal their incredible history.

最大的湖泊北美中部有五个湖泊，都由河流连接。 这些湖不是普通的湖。 它们就是五大湖。它们加起来拥有地球上超过20%的淡水。 如果五大湖均匀分布，它们的水将淹没美国大陆3米(9英尺)深!像大海一样，五大湖有波浪、强劲的洋流，甚至还有微小的潮汐。 这些巨大的湖泊从何而来? 五大湖的形成要追溯到最近的冰河期。 这些湖泊，以及湖泊周围和湖底的土地，展现了它们不可思议的历史。

The Great Glaciers Across Canada and the northern United States, saber- toothed cats and mammoths once roamed snow-covered lands. This ice age lasted from about 110,000 to 12,000 years ago. It was just one of a series of "cold snaps" that have hit Earth over the past 2.5 million years. Scientists call these cold snaps glacial periods. During the last glacial period, snow accumulated and never melted. Over thousands of years, the snow became tightly packed under its own weight. It formed enormous sheets of ice. These ice sheets spread and grew up to 3 kilometers (1.8 mi.) thick.

在加拿大和美国北部，剑齿虎和猛犸象曾经在冰雪覆盖的土地上漫步。 这个冰河期从11万年前持续到1.2万年前。 这只是过去250万年间袭击地球的一系列“寒流”之一。 科学家称这些寒潮为冰期。 在最后一个冰川期，雪堆积而不融化。 几千年来，雪在自身的重压下变得紧密。 它形成了巨大的冰层。 这些冰原扩张并增长到3公里(1.8英里)厚。

Sculpted by Ice The heavy ice sheets acted like bulldozers as they grew and shifted. They scraped away at the rock and pushed away soil. The land beneath the ice sheets sank down under the heavy weight of the ice. During each glacial period, ice sheets scooped and pushed away more land. By 12,000 years ago, they had carved enormous basins in the middle of North America As Earth slowly warmed up again, the ice sheets melted and water flooded the low-lying basins. This process formed the Great Lakes.

厚重的冰原在生长和移动时就像推土机一样。 他们刮开岩石，推开泥土。 冰原下的土地在冰的重压下下沉。 在每一个冰川时期，冰原都会铲走更多的陆地。 到12000年前，它们在北美中部雕刻出了巨大的盆地。随着地球再次缓慢变暖，冰盖融化，水淹没了低洼的盆地。 这一过程形成了五大湖。

Today's Great Lakes There are five main Great Lakes that flow from one to the next in a single system of fresh water. Lake Superior "Superior" is more than just a name. Lake Superior has the largest surface area of any lake on Earth and contains Earth's third-largest volume of fresh water. That's more water than all the other Great Lakes combined.

今天的五大湖有五个主要的五大湖，它们在一个单一的淡水系统中从一个湖流向另一个湖。 苏必利尔湖"苏必利尔湖"不仅仅是一个名字。 苏必利尔湖是地球上面积最大的湖泊，拥有地球上第三大淡水容量。 这比其他五大湖的水量加起来还要多。

Lake Huron and Lake Michigan Water flows out of Lake Superior and down the St. Mary's River into Lake Huron. Lake Huron is connected to Lake Michigan by the Straits of Mackinac (MA-kuh-naw), which are 8 kilometers (5 mi.) wide. Since water flows back and forth through the straits, some scientists consider Lake Michigan-Huron to be one huge lake. Lake Huron contains the largest island in a body of fresh water on Earth. Manitoulin Island has its own lakes. Some of these lakes even have their own islands! Lake Michigan is only connected to the other lakes through Lake Huron. It is also the only Great Lake entirely within the United States.

休伦湖和密歇根湖湖水从苏必利尔湖流出，沿着圣。 玛丽河流入休伦湖。 休伦湖由麦基诺海峡(MA-kuh-naw)连接到密歇根湖，宽度为8公里(5英里)。 由于水在海峡中来回流动，一些科学家认为密歇根休伦湖是一个巨大的湖。 休伦湖拥有地球上最大的淡水湖岛屿。 马尼图林岛有自己的湖泊。 有些湖泊甚至有自己的岛屿!密歇根湖只通过休伦湖与其他湖泊相连。 它也是唯一一个完全位于美国境内的大湖。