WWC - Glaciers Lesson

 

Glaciers

Glaciers are one of the most impressive land altering forces. Glaciers are multi-year accumulations of ice and snow that occur at high latitude and high altitude regions on Earth. Since the snow and ice don't completely melt away every year, additional buildup occurs annually, eventually forming a sheet of ice that is so heavy that it actually deforms (bends) under its own weight. The weight of the ice also causes it to slowly slide downhill, so the majority of glaciers are found in the valleys of mountain ranges.

The weight of the ice forcing the glacier downhill deforms the ice even more, so it literally follows the bends of the valley. Viewed from afar, many glaciers look like frozen rivers. As they move downhill, the front of the glacier (called the terminus) plows into the ground, bulldozing soil, boulders, and rock fragments in front of it. This pile of material builds up as the glacier progresses, forming a moraine (imagine a bulldozer pushing dirt and rocks in front of it to get an idea of what a moraine might resemble).

You might think that the underside of a glacier is smooth, but it is actually embedded with boulders that are frozen in it. As a result of the bulldozing motion of the terminus and the scouring action of the underside, the ground beneath a glacier is wiped clean of loose rock and soil. When a glacier recedes due to melting, nothing but bare rock is left behind.

Glaciers that reach the ocean will push out over the water until the weight of the ice causes huge chunks to break off, forming icebergs. Icebergs are often blue due to the fact that the weight of the ice accumulation actually forces out any bubbles in the frozen water that makes up the glacier (microscopic bubbles trapped in ice give it a white appearance, while ice without bubbles absorbs most colors of light except for blue).

Due to the enormous size of the ice sheets (both in surface area and thickness), glaciers have been major contributors to the creation of geologic landforms. During the last ice age, North America was covered with glaciers - some over a mile thick - that extended south as far as southern Illinois. On the eastern coast the terminus reached the ocean, and the resultant moraine is now known as Long Island, New York. The weight of the ice mass scoured out deep depressions that filled with fresh water when the glacier eventually melted about 14,000 years ago, forming the Great Lakes.

 

 

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