Glacial Processes

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Water gets into cracks in rocks

Freezes when temp. reaches below 0°C

Puts pressure on surrounding rock as it expands

When water melts, pressure = released

Repeated freezing & thawing widens cracks

Jagged pieces of rocks break off

http://www.youtube.com/watch?v=jFU6j8qD-84 (Embed)

Snow fills existing hollows on the hillside

Over many years, it turns to ice

When the hollow is full, the ice moves downhill as a corrie glacier

Freeze-thaw and plucking make backwall steep

Moraine dragged along the base of corrie glacier makes hollow deeper by abrasion

A lip gets left because erosion is less here. Also sometimes moraine is deposited

After the ice age, melt water was trapped by the lip making a small lake or tarn

Plucking

Rocks stick and freeze to the bottom or sides of a glacier

Plucked away from bedrock

Deposited

Leaves behind jagged rocks

Abrasion

Moraine embedded into glacier rubs against floors and sides of valley as it moves

Leaves behind smooth surface like sandpaper

Glacier wears away sides & floor of the valley

Causes valley to deepen, widen & straighten

When ice melts, a U-shaped valley with steep sides & flat floor is left

Narrow floors

Steep-sided

Straight wide flat floors with truncated spurs

Interlocking spurs are eroded away to leave cliff-like truncated spurs

Glaciers perched up on valley sides as hanging valleys

During the ice age many river valleys were filled with snow which turned to ice and moved down the slope as glaciers

Freeze-thaw weathering supplied the glacier with sharp rock fragments

Ice plucking & abrasion eroded the valley side & floor leaving a flat bottomed & steep sided valley known as glacial trough

Glacier scraped away interlocking spurs of the river valley leaving truncated spurs

Tributary valleys were left hanging above the main valley

After the ice melted, glacial troughs often filled with lakes called ribbon lakes because they are long & thin

Freeze-Thaw Weathering

Corrie

Erosion

U-Shaped Valley

Truncated Spurs & Hanging Valleys