Glaciated Upland Landscapes & Past Glacial Processes (Edexcel GCSE Geography A)

Past Climate & Impact on Glacial Processes

• The Earth's climate is continuously changing

• There have been colder (glacial) and warmer (interglacial) periods

• In the last one million years, there have been approximately 10 glacial cycles

• In the UK, this led to three main glacial periods

The UK's Ice Age

• Europe's last ice age peaked 20,000 years ago and ended about 11,500 years ago during the Pleistocene

• At this time, 30% of the world's land was covered in ice

• Temperatures remained below 0°C all year round in northern regions, particularly Scotland, allowing a 1 km thick ice sheet to cover most of the country

• During the ice age, areas covered in ice were weathered and eroded to create dramatic mountain scenery

• Today, much of upland Britain is covered in u-shaped valleys along with steep, eroded mountain peaks

• After the ice age at the end of the Pleistocene, temperatures increased

  • Ablation was greater than accumulation so the glaciers retreated

  • Previously covered areas were exposed as deep valleys with sediment deposits

UK's glaciated landscape

What is a glacier?

• Glaciers are large, slow-moving rivers of ice

• Giant glaciers are called ice sheets

• Glacial ice is formed from layer upon layer of falling snow every year

  • The weight of the snow compresses the layers of snow below

  • The air is forced out and ice forms

  • It takes 20 to 30 years for the layers to compress and form glacial ice

• Glaciers will grow in size if the temperature stays below 0°C

Types of glaciers

• An ice sheet is an area of glacial ice covering more than 50,000km²

• A valley glacier is an area of glacial ice contained within a valley

Glaciers as a system

• Glaciers have inputs (snow and avalanches) and outputs (meltwater)

• The zone of accumulation is where the input of snow is greater than the output

• The zone of ablation is where the output of meltwater is greater than the input of snow or where calving occurs

• The glacial budget is the difference between accumulation and ablation

  • When accumulation is greater than ablation, the glacier advances

  • When accumulation is less than ablation, the glacier retreats

Formation of a glacier

Glacial Erosion, Transport & Deposition

Glacial erosion

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

• Plucking:

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

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

  • This meltwater then 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 way

• 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 erosion

Glacial movement

• Glaciers move under gravity very slowly

  • Basal sliding occurs when friction between the glacier and the surface causes a thin layer of ice at the base to melt

    • This thin layer of meltwater acts as a lubricant to help move the glacier downhill

  • Internal flow happens when ice crystals within the glacier slide over each other, changing the shape and size of the glacier

Glacial transport

• 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 with the sheer force of the moving ice

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

Glacier cross-section

Glacial deposition

• During the warmer summer months, glaciers begin to melt and deposit material (till) held in the glacier

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

  • Glacial till is deposited on the valley floor or sides directly by the moving glacier

  • Fluvioglacial till is sediment deposited by streams flowing from the melting glacier

• Deposition can also occur when the glacier passes over an obstruction and the material becomes stuck

• Meltwater rivers carry large amounts of glacial till

  • The till will be further eroded by attrition to become outwash 

  • This finer till is sorted

  • When the energy of the river reduces, the outwash is deposited in layers further down the valley on the outwash plain

Glacial till and outwash