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Glacial Erosion and Deposition Erosion • Glaciers have the capacity to carry huge rocks and piles of debris over large distances • They grind out parallel scratches in the bedrock – Small scratches are called grooves and larger ones are called striations • As valley glaciers erode the land over which they move, they carve out various U-shaped valleys and mountain landforms: Cirques, Aretes and Horns Deposition • Glacial deposits are unsorted, unlayered deposits of various types • Particles carried by a glacier tend to have an angular to round shape and a rough texture • Much of the debris is left behind in ridges called moraines – Terminal moraines mark the farthest advance of a glacier Moraines Glacial Sediment • Till is the unsorted rock material directly deposited by glacial ice Glacial Sediment Erratic – a large rock deposited by a glacier Glacial Sediment • Drumlins – canoe shaped hills of unsorted sediments that form as a glacier moves over the land • They indicate the direction of glacial movement Outwash Plains • Beyond the terminal moraine, meltwater runs and carries sediments of gravel, sand, silt and clay • These are deposited in sorted layers as they are being deposited by running water as a result of the melting glacier (not by the ice directly) Outwash plain in front of Thompson Glacier, Axel Heiberg Island, Canadian Arctic When the glacier melts/retreats: • Gouges out land that becomes filled with meltwater forming lakes (Finger Lakes) • Scoops out shallow basins that fill with water called kettle lakes Formation of Kettle Lake Kettle Lakes Toe of a valley glacier: • Glacier Review