Glacial Processes

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

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