4 – Glacial Erosion

glacier – a mass of ice and snow that moves downhill under the influence of gravity. Salmon Glacier in British Columbia, Canada. Kenai Fjord National Park, Alaska, USA.

glacier – a mass of ice and snow that moves downhill under the influence of gravity. There are two types of Glaciers; 1 – Mountain (alpine or valley) glaciers.

2 – Continental (ice sheets)

Glacier movement glaciers always move downhill. advancing glaciers more snow and ice accumulate than is lost by melting. the end of the glacier will move forward.

retreating glaciers more ice and snow melt each year than accumulate. the furthest extent of the glacier (the end) does not extend as far downslope.

Ice Movement the ice within a glacier moves more slowly along the sides of the glacier (friction). View of ice velocity from above glacier (http://www.physicalgeography.net/fundamentals/10ae.html)  View of ice velocity from side of glacier (http://www.physicalgeography.net/fundamentals/10ae.html)

Glacial Erosional Features

Till Unsorted (different sizes) & unstratified (not layered) rock material deposited directly by glacial ice.

Moraine a deposit of till left behind when a glacier retreats.

End moraine, Bylot Island, Canada

Lateral moraine material that piles up along the sides of the glacier.

Medial moraine a pile of material that runs down the middle of the glacier. produced when two glaciers come together and their lateral moraines join.

Striations long parallel scratches left on rocks and bedrock by glacial movement. produced when the glacier drags rock material over the bedrock.

Glacial grooves, Ontario, Canada

U-shaped valley glacial valley - a u-shaped valley formed by glacial erosion.

Hanging valley The U-shaped valley carved out by the main glacier is deeper than the valleys carved out by the tributary glaciers.

Cirque a semicircular basin found at the head of a glacial valley.

Cirque, Torngat Mountains, Newfoundland, Canada

Arete a sharp divide that separates two adjoining cirques. “A knife-like ridge.”

Horn a pyramid-shaped peak formed where three or more cirques meet. Matterhorn, in Switzerland.

Torngat Mountains, Newfoundland, Canada

GLACIAL DEPOSITIONAL FEATURES

Till unsorted and unstratified rock material deposited directly by glacial ice.

Outwash sediments deposited in front of a glacier by streams of meltwater.

End Moraine a moraine that occurs at the ice front - rock pieces brought forward by the glacier’s motion build up as the ice melts.

End moraine, Bylot Island, Canada

Erratic a large boulder that has been transported into an area by a glacier.

Perched erratic boulder, North West Territories, Canada Perched erratic boulder, Newfoundland, Canada

Drumlin a long, smooth, canoe-shaped hill. usually found in groups. shaped by an advancing glacier.

Drumlin field. Manitoba, Canada

Outwash Plain a broad, stratified (layered), gently sloping deposit of sediment. formed beyond the terminal (end) moraine by streams from a melting glacier.

Southwest Alaska 1996

Esker a long, winding ridge. formed when sand and gravel fill meltwater tunnels beneath a glacier.

Kettle (kettle hole) a bowl-like hollow found in deposits of glacial outwash. formed when a large block of ice was left behind when a glacier melted.