Glaciation in the UK (AQA GCSE Geography)

The UK's ice age

• Europe's last ice age peaked 20,000 years ago and ended about 11,500 years ago
• 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 1km thick ice sheet to cover most of the country
• Ireland, Wales, northern England, Scotland, and the midlands were covered in perpetual ice 
• Much of the country was uninhabitable for humans
• Today, much of upland Britain is covered in u-shaped valleys along with steep, eroded mountain peaks
• During the ice age, areas covered in ice were weathered and eroded to create a dramatic mountain scenery
• After the ice age, those areas were exposed as deep valleys with sediment deposits

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
• 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
• Glaciers shape our landscape

• Glaciers create distinct landforms through weathering, erosion, transportation and deposition
• Freeze-thaw weathering happens when rocks contain cracks and where temperatures regularly dip below the freezing point
• Any water in the cracks will freeze as the temperature drops, which expands 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 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

• 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

• 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

Glacial till                                                                                   Glacial outwash plain