What is a glacier? In places where the summers are not warm enough to melt the snow that falls each winter, the snow can accumulate year after year, eventually forming huge sheets of ice called glaciers. When the ice becomes thick enough—about 150 feet—pressure at the bottom becomes so great that this ice deforms and flows plastically.
Lower Sea Level Glaciers “lock up” tremendous amounts of water, keeping it from returning to the sea and thereby causing sea level to fall.
Sculpt the Landscape Massive and slow-moving, glaciers are capable of pushing millions of tons of earth before them as they flow.
Carry Rocks and Boulders As glaciers flow, they pick up rock and sediment by the ton, carrying it sometimes hundreds of miles from its original source.
Deposit Sand and Gravel
Flowing glacial meltwater carries with it huge amounts of sand and gravel previously trapped within the glacier.
Twenty-one thousand years ago, a glacier thousands of miles wide and more than a mile thick in places covered much of the North American continent.
As they grew and spread, these continental ice sheets flowed slowly under their own immense weight, moving anywhere from a few inches to a few feet in a given year -- many hundreds of miles over thousands of years. As they moved, they dramatically altered the landscape beneath and around them. They sculpted the sides of mountains and picked up and carried millions of tons of rock and earth frozen into the ice.
As the ice sheets melted, this material was carried away in rivers of glacial meltwater, depositing tons of earth, sand and gravel in glacial lakes and stream beds. The glaciers also dramatically affected coastlines, lowering the sea level as they trapped huge quantities of the earth’s water on land. As they melted, the glaciers released this water into the oceans, raising sea level, submerging land, and leaving us the familiar coastlines that we know today.
