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Glaciers are the most natural and beautiful ice sculptures on earth. The beginning of a glacier is created when snow falling in sheltered areas of the mountains does not reach melting temperature. As more layers of snow is added year after year, the build up becomes so thick and heavy that the weight presses down on the lower layers compressing them into ice. Continued pressure on these ice layers cause them to twist and flow. It may be hard to imagine something as hard and brittle as ice actually flowing. But even rocks when put under great pressure will take on a flowing consistency.
Once the ice has reached this consistency it then moves downhill toward any available valley and away from the shelter area where it formed. As it moves it grinds the rocks along the valley sides and bottom until it gradually carves out a deep channel. It then continues down this channel until it reaches a lower area where temperatures are higher and eventually melts. The slow movement of a glacier literally inches it forward each year. A glaciers tremendous weight is what makes it so powerful.
Scientist have learned that glaciers move faster near their center than at the edge even though the flowing ice cannot be seen on the surface. The bottom of the glacier where the pressure is the greatest is where the ice flows form. Ice on the surface is brittle and hard. As the ice moves beneath it, the surface ice becomes torn and cracked forming deep cracks called crevasses. Glaciers also form what is called seracs or spiky pinnacles of ice when they turn a corner or flow over a hump. In areas such as the North or South poles that have high latitudes, glaciers are known to cover complete land masses. This has been evident in areas like Antarctica where these ice sheets flow outward to the sea tearing up rocky materials and taking it with the flow.
Ice caps covered most of North America and northern Europe during the last two million years. It retreated and advanced several times with thousands of years between its movement. When the ice caps retreated the weather became even warmer than it is today.