Glacial Processes (DP IB Geography)

Glacial Erosion

• Glaciers create distinct landforms through weathering, erosion, transportation and deposition

• Freeze-thaw weathering happens when rocks contain cracks and temperatures regularly dip below the freezing point

• Any water in the cracks will freeze as the temperature drops, which will expand as it freezes, exerting pressure on the crack

• Repeated freezing and thawing of water will eventually break the rock apart

• After glaciers break down the rock through freeze-thaw action, erosion continues the process by plucking and abrasion

• Plucking:

  • As a glacier moves through a valley, pressure is exerted on the sides and bottom of the valley

  • This generates friction and heat, causing the edges of the glacier to melt a bit

  • This meltwater freezes around rocks and stones under the glacier

  • As the glacier moves forward, it 'plucks' this ice, pulling the rock away 

• Abrasion:

  • Abrasion occurs as bits of rocks, stones and boulders stuck in the ice, grind against the rock below the glacier, wearing it away and leaving scratch marks called striations across the rock

• It is the weight of the ice in a glacier which forces it to advance downhill, eroding the landscape as moves

• Ice advances in a circular motion called rotational slip, which hollows and deepens the landscape

Glacial Transportation

• Glaciers move under gravity very slowly

• Glaciers transport material such as clay, rock, and sand in the body, base and surface of the glacier over long distances

• The front of a glacier is called the 'snout' and acts as a bulldozer pushing loose rocks and debris downhill by the sheer force of the moving ice

• Rotational slip is the circular motion of the ice in a hollow 

• Due to the weight of the ice, friction at the base of the glacier melts the ice and the glacier will move on a film of meltwater

• Any material carried or moved by the glacier is called glacial till

Glacial Deposition

• During the warmer summer months, glaciers begin to melt, and glacial till is deposited on the valley floor or sides of a moving glacier

• Till is unsorted, irregular debris ranging from clay to boulders of any size and shape 

• Meltwater will also flow out of the glacier's snout forming meltwater rivers

• These rivers carry large amounts of glacial till, which will undergo further erosion through attrition to become outwash 

• This finer till is sorted and when the energy of the river reduces, the outwash is deposited in layers further down the valley on the outwash plain