A glacier is a huge mass of ice on land or is floating in the sea next to the land. It moves extremely slow. Think of a glacier moving like a river of ice; however, the glacier's movement cannot easily be seen. They appear to be sitting still. As glaciers do move, some of them may merge with other glaciers.
Nearly all the glaciers in the world are found near the North and South Poles, but others exist in the highest mountain ranges such as in the Andes Mountains in South America, the Himalayan Mountains located across the northeastern portion of India, and in the Alps of Western Europe. Other places glaciers can be found include Greenland, Iceland, Canada, Alaska, and even in California as part of the Sierra Nevada mountain range.
The country of Greenland is mostly a giant ice cap, and the ice is about 2 miles thick in some areas. The Bering Glacier in Alaska is the longest in the United States at 125 miles. There have been many land formations that resulted due to the movement of glaciers during the Ice Age, a period in the Earth's history when these massive slowly moving sheets of ice covered much of the Earth's surface. The last ice age on Earth occurred about 11,000 years ago. About 1/3 of the surface was covered in ice.
At the end of this ice age, glaciers were left behind, and the sheets of ice covered rivers and valleys. Over the next 1,000 years, the Earth began to warm, and the remaining glaciers melted leaving lakes and valleys with a mixture of rocks and soil. In higher elevations, some of the ice is left over from the Ice Age.
The formation of glaciers occurs when un-melted snow builds up, compresses, and then turns into solid ice. Imagine yourself making a snowball, packing it tightly together, and then placing it in a freezer. After a short period of time, the ball is now ice, and you might think of it as a mini-glacier. In real life though, the glaciers on the Earth's surface will take hundreds of years to form. Glaciers may sometimes appear blue in color too. This is due to tiny air bubbles being forced out by increasing pressure within the glacier as it forms.
In the regions glaciers form, it is so cold that when a snowflake hits the ground it does not melt but combines with the larger grains of ice. In addition, glaciers cannot form unless the region is above the snowline, which is the lowest elevation where snow can remain throughout the year. Therefore, glaciers form in high-altitude mountains.
There are two main categories of glaciers: Alpine and Continental. Alpine are those that form in the mountain, and continental is masses of ice that are large and continuous, bigger than an alpine glacier. There are subtypes of both categories. The four types of alpine glaciers include cirque, forming on the slope of a mountain; valley, filling a valley between two mountains; Piedmont, when two or more glaciers form usually at the edge of a mountain; and Tidewater, a glacier that meets the sea, and when a piece breaks off, the floating mass of ice is known as an iceberg.
The three types of continental glaciers include ice sheets, the largest of all glaciers located only in Antarctica and Greenland; ice caps, like an ice sheet but only smaller; and an ice field, a smaller version of an ice cap and does not cover the land entirely, some parts of the land pokes through the ice.
Glaciers have shaped the surface of the Earth since the beginning of time. The ice sheets described above are so large and heavy they can bend the continental crust of the earth.
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