During the ice ages, glaciers covered much of the land. Today glaciers are located in 15 states and all over the world from the Alps in Europe, to the mountains of Chile. These slow moving rivers of ice are powerful enough to reshape the land. By melting and refreezing, they pick up and retain rocks and other debris within the ice. As the glaciers move, the debris can leave scratch marks on the landscape.
To learn about glaciers we first watched two exciting documentaries from the How the Earth Was Made series.
How the Earth Was Made - Iceland
The geography of Iceland is very unique. Volcanic activity rages underneath massive glaciers. The intensive heat melts the ice and results in massive floods. The floods carry huge boulders downward, while the glacier movement carves the landscape.
How the Earth Works - Yosemite
Yosemite was formed through volcanic and glacial activity. Although most glacier valleys have U-shaped bottoms, the Yosemite valley was V-shaped. Despite this opposing evidence, the naturalist John Muir was convinced glaciers played a role in the history of Yosemite. He saw evidence of glacier created scratches on rocks in the valley which were familiar to him from his time spent in the glaciers of Europe. The moraines present in the valley were further indications of glacial activity.
His theories were proven many years later. After the glaciers receded, the valley was filled with a lake. Sediment from the lake filled in the valley which was later carved into a V-shape by river activity.
After learning a bit about glaciers we tried several activities from How the Earth Works (How It Works).
There are two basic ways in which glaciers move. In basal slip, the bottom of the glacier picks up bits of debris as it passes over the land. In plastic deformation, the bottom layer of ice deforms due to the intense amount of weight above.
Moraine and Valley Formation
A moraine is a pile of debris located at the end of a glacier. As a glacier moves, the rocks, boulders, trees and other matter are pushed along in front much like a snow plow. When the glacier melts, the debris pile remains as evidence of glacial activity.
As it melted, a valley was formed below the glacier.
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