Chapter 13: Glacial Processes, Patterns and Associated Landforms

1. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Glaciation • Earth once covered with glaciers • Last glaciation ended around 10,000 years ago • Current interglacial period – Holocene • Two major glaciations have affected Ireland: • The Munsterian, 300,000 to 132,000 years ago • The Midlandian, 79,000 to 13,000 years ago

2. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Glaciers • Rivers of ice that move slowly • Move downslope under the influence of gravity and the pressure of own weight • Form where rate of accumulation of snow and ice is greater than rate of melting • Largest reservoir of fresh water on Earth

3. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Types of glaciers • Valley glaciers: form in mountainous locations and move down valleys • Continental ice sheets/glaciers: enormous areas of glacial ice and snow

4. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Causes of an ice age • Change in the Earth’s orbit around the sun • Change in the angle of the Earth’s axis

5. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Processes of glacial erosion Glaciers erode the landscape they travel over in two ways: • Plucking • Abrasion

6. Chapter 13: Glacial Processes, Patterns and Associated Landforms • 1. Plucking Most effective where: • Rock is well jointed • Rock has already been weakened by freeze-thaw action • Bottom of glaciers scrape along valley floors – creates friction causing melting around the base of the glacier • Meltwater refreezes • Freezes around the rocks on the valley floor and these become part of the glacier • Glacier advances • Newly trapped rock is plucked out of the valley floor • New material is then used in process of abrasion

7. Chapter 13: Glacial Processes, Patterns and Associated Landforms • 2. Abrasion • Occurs when the bedrock beneath the glacier is eroded by the debris/material embedded in the sides and bottom of the glacier • ‘Sandpaper effect’ – scrapes the rock over which it is travelling and leaves scratches or grooves in the rock • Striations – show the direction of the ice flow

8. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Processes of glacial transportation • Basal sliding • Friction between the base of the glacier and the valley floor • Meltwater acts as a lubricant • Glacier slides downslope under the influence of gravity • Internal flow • Ice crystals react to pressure and gravity • Melting and refreezing • Ice changes internally over time without completely melting or breaking

9. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Factors affecting the rate of glacial erosion • Thickness of ice • Topography • Geology • Gradient • Accumulation and ablation

10. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Landforms of glacial erosion • Cirque • Birthplace of a glacier • Depression in a mountain • Three steep sides • Also called a corrie or coom • Arête • Narrow ridge • Formed when two cirques formed side-by-side or back-to-back

11. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Landforms of glacial erosion (continued) 3. Pyramidal peak • Formed when three or more cirques are eroded back-to-back or side-to-side around the sides of a mountain • Isolated peak in the centre

12. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Landforms of glacial erosion (continued) 4. U-shaped valley • Glaciers take the easiest route as they move from upland areas down through their valleys • Route is often a pre-existing V-shaped river valley • Glacier moves through this valley, changing the shape from a V-shape to a U-shape • Erode vertically and laterally • Valleys have steep sides and flat floors • Glacier cuts off interlocking spurs of the V-shaped valley leaving truncated spurs

13. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Landforms of glacial erosion (continued) 5. Ribbon lakes • Long, narrow lakes found in glaciated U-shaped valleys • As a glacier advances through its valley it abrades the landscape • Soft rock is abraded faster and easier than the harder resistant rock forming basins • Within the rock basin meltwater and rainwater accumulates forming a ribbon lake 6. Fjords • Drowned U-shaped valleys • Result of melting glaciers

14. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Glacial deposition • Dropping or laying down of sediment that was once transported by a glacier • Lowland areas • Deposited material is called glacial drift • Material deposited directly by ice is called till or boulder clay • Material deposited by glacial meltwater is known as fluvio-glacial deposits

15. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Examples of landforms of glacial deposition • Moraines • Drumlins • Erratics

16. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Examples of landforms of fluvio-glacial deposition • Eskers • Outwash plains • Kames and kettleholes

17. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Landforms of glacial deposition • Moraine • Deposited debris • Various sizes ranging from large boulders to fine rock flour • Material may be angular or rounded in shape

18. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Five types of moraine • Lateral moraine • Medial moraine • End/terminal moraine • Ground moraine • Englacial moraine

19. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Landforms of glacial deposition 2. Drumlins • Oval-shaped hills consisting of boulder clay • Show direction of glacier movement • Occur in swarms or cluster • ‘Basket of eggs’ topography • ‘Drowned drumlins’ – as the ice melted sea levels rose and the drumlins appear as islands in the sea

20. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Landforms of glacial deposition 3. Erratics • Material transported by the glacier and are said to be ‘out of place’ when deposited • Provide information about the direction of the glacier and how far it has travelled – crag and tail • Esker – long winding ridges of stratified sand and gravel that wind its way across lowland areas

21. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Landforms of glacial deposition 4. Outwash plains • Glaciers melt • Release vast amounts of water • Spreads outwards beyond the end/terminal moraine • Carries large volumes of rock and gravels and sands

22. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Landforms of glacial deposition 5. Kames • Piles of sediment consisting of gravels and sand • Deposited along the front of a retreating glacier

23. Chapter 13: Glacial Processes, Patterns and Associated Landforms • Landforms of glacial deposition 6. Kettle holes • Blocks of ice separate from the main glacier • Buried partly in meltwater sediments • Blocks of ice melt leaving depressions or holes • Fill with water – form kettle hole lakes