Chapter 13: Glacial Processes, Patterns and Associated Landforms
description
Transcript of Chapter 13: Glacial Processes, Patterns and Associated Landforms
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
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
Chapter 13: Glacial Processes, Patterns and Associated Landforms
Types of glaciers
1. Valley glaciers: form in mountainous locations and move down valleys
2. Continental ice sheets/glaciers: enormous areas of glacial ice and snow
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
Chapter 13: Glacial Processes, Patterns and Associated Landforms
Processes of glacial erosion
Glaciers erode the landscape they travel over in two ways:
1. Plucking
2. Abrasion
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
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
Chapter 13: Glacial Processes, Patterns and Associated Landforms
Processes of glacial transportation
1. 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
2. Internal flow• Ice crystals react to pressure and gravity
• Melting and refreezing
• Ice changes internally over time without completely melting or breaking
Chapter 13: Glacial Processes, Patterns and Associated Landforms
Factors affecting the rate of glacial erosion
• Thickness of ice
• Topography
• Geology
• Gradient
• Accumulation and ablation
Chapter 13: Glacial Processes, Patterns and Associated Landforms
Landforms of glacial erosion
1. Cirque
• Birthplace of a glacier
• Depression in a mountain
• Three steep sides
• Also called a corrie or coom
2. Arête
• Narrow ridge
• Formed when two cirques formed side-by-side or back-to-back
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
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
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
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
Chapter 13: Glacial Processes, Patterns and Associated Landforms
Examples of landforms of glacial deposition
• Moraines
• Drumlins
• Erratics
Chapter 13: Glacial Processes, Patterns and Associated Landforms
Examples of landforms of fluvio-glacial
deposition
• Eskers
• Outwash plains
• Kames and kettleholes
Chapter 13: Glacial Processes, Patterns and Associated Landforms
Landforms of glacial deposition
1. Moraine
• Deposited debris
• Various sizes ranging from large boulders to fine rock flour
• Material may be angular or rounded in shape
Chapter 13: Glacial Processes, Patterns and Associated Landforms
Five types of moraine
I. Lateral moraine
II. Medial moraine
III. End/terminal moraine
IV. Ground moraine
V. Englacial moraine
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
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
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
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
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