GLACIATION

• Glaciation


  Periods when the Earth was a lot colder than today, with snow and ice building up over long periods of time
• The last ice age began

  2.38 million years ago
• Ice age


  Periods with both warmer and colder periods, with the colder periods called glaciations
• During the last glaciation, a large ice sheet 3km deep moved across northern Europe and covered most of Ireland
• The current warm period began, when the ice sheet covering Ireland began to melt


  About 12,000 years ago
• Valley glaciers


  • Smaller rivers of ice that moved downhill due to gravity, eroding the landscape and transporting sediment
• Greenland and Antarctica are still covered with ice sheets, and valley glaciers can be found in the Alps and the Himalayas today
• Glacial erosion


  The processes of plucking and abrasion that erode the landscape
• Plucking


  The pulling of rock from the ground by the weight and friction of the glacier
• Abrasion


  The grinding of rocks against the landscape by the glacier, leaving scratches called striations
• Meltwater erosion


  Erosion caused by the huge volumes of water flowing off glaciers, sometimes bursting forward and eroding the landscape
• Glacial transportation


  Glaciers transport unsorted, loose rock in long ridges called moraines
• Types of moraines


  • Lateral moraines
  • Medial moraines
  • Ground moraines
  • Terminal moraines
• Lateral moraines


  Ridges of sediment deposited on the sides of a glacier
• Medial moraines


  Ridges of sediment formed when two glaciers meet and their lateral moraines join together
• Ground moraines


  Material plucked from the valley floor by the glacier and deposited at the base
• Terminal moraines


  Ridges of weathered material deposited at the furthest point the glacier travelled
• Glacial deposition


  Sediment deposited directly by the melting ice or indirectly by meltwater
• Glaciers erode the landscape by plucking rocks from the ground, transporting them as moraines, and eventually depositing them
• Valley glacier


  A smaller river of ice that moves downhill due to gravity
• Cirques and arêtes


  • Coumshingaun in Co. Waterford
  • Upper and Lower Lough Bray in Co. Wicklow
• Cirque


  A large armchair-shaped hollow containing a lake, formed by erosion
• Arête


  A steep, knife-edged ridge formed between two cirques or hanging valleys
• 1. shaped valley


  A glaciated valley with steep sides and a wide, flat floor, formed by erosion
• Pyramidal peak


  A steep-sided mountain formed when a number of cirque glaciers form around a mountaintop
• Hanging valley


  A smaller valley that hangs above the level of the main valley, formed when a smaller tributary glacier joins a larger glacier
• Fjord


  A drowned U-shaped valley found on the coast, formed in the same way as a U-shaped valley but flooded by rising sea levels
• Drumlin


  An oval-shaped hill made of boulder clay, a feature of glacial deposition
• Esker


  A long, narrow ridge of sorted gravel and sand, formed from glacial meltwater deposits
• The drumlin belt stretches from Co. Down to Co. Mayo, and drowned drumlins can be seen in Clew Bay, Co. Mayo
• The Esker Riada runs between Dublin and Galway, with most of it covered in forestry
• Co. Mayo
• Figure 12.12 An 05 map showing a wa of drowned drun in Clew Bay, Co. Mayo
• Figure 12.13 An aerial photograph of Clew Day
• Eskers


  Long, narrow ridge of sorted gravel and sand, up to 30m in height, formed from glaciation processes
• Esker formation


  1. Tunnels form under glacier

  2. Tunnel becomes choked with sediment

  3. Meltwater stops flowing

  4. Larger particles deposited first, followed by smaller particles (sorting)

  5. As glacier retreats, narrow winding ridge of sediment emerges
• Erratics


  Boulders of one rock type deposited in an area with a different rock type, can be deposited by glacier or meltwater
• Outwash plain


  Flat area of gravel and sand found in lowland areas, formed when meltwater from a glacier deposits sediment as it loses energy
• As glaciers melted, they deposited the sediment they were carrying. Eskers, drumlins and outwash plains are common landforms of glacial deposition
• Glaciated landscapes are an important resource. People have been attracted to them for centuries as ways of making a living or for tourism