Transcript CHAPTER 1 THE TECTONIC CYCLE

Glaciation
5th year Geography
Ms Carr
Learning Intention
• Visualise what glaciation is.
• Name and briefly explain the formation of
glacial landforms.
• Recognise the landforms on a diagram, OS
map and Aerial photograph.
Glaciation
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Earth once covered with glaciers
Last glaciation ended around 10,000 years ago
Current interglacial period – Holocene
Two major glaciations have affected Ireland:
i.
ii.
The Munsterian, 300,000 to 132,000 years ago
The Midlandian, 79,000 to 13,000 years ago
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.
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 & 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
Processes of Glacial Erosion
Glaciers erode the landscape they
travel over in two ways:
1.Plucking
2.Abrasion
Textbook page 146
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
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
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
 Material transported by the
glacier is called moraine.
Chapter 13: Glacial Processes, Patterns & Associated Landforms
Factors affecting the rate of glacial erosion
 Thickness of ice
 Topography
 Geology
 Gradient
 Accumulation and ablation
Landforms of Glacial Erosion
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Cirque / Corrie
Arete
Pyramidal Peak
U-Shaped Valley
Ribbon Lake
Fjords
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
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
& Associated Landforms
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
• 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
Fjords
Drowned U-shaped valleys
Result of melting glaciers
OS Map
• Textbook page 149
Pairwork Quick Questions
• Name two processes of glacial erosion.
• What is the name given to material that is
transported by the glacier?
• Name the landform that is said to be the
birthplace of a glacier.
• How is an arete formed?
• Explain the formation of a ribbon lake.
Homework
• Textbook page 159
• Questions 1-4
Landforms of Glacial Deposition
• Moraines
• Drumlins
• Erratics
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 & Associated Landforms
Examples of landforms of fluvio-glacial deposition
 Eskers
 Outwash plains
 Kames and kettle holes
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 & Associated Landforms
Five types of moraine
i.
Lateral moraine
ii. Medial moraine
iii. End/terminal moraine
iv. Ground moraine
v. Englacial moraine
Drumlins
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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
OS Map
• Textbook page 155
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 & Associated Landforms
Examples of landforms of fluvio-glacial deposition
 Eskers
 Outwash plains
 Kames and kettle holes
Eskers
• Long winding ridges of stratified sand and
gravel.
Outwash Plains
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
Kames
 Piles of sediment consisting of gravels and sand
 Deposited along the front of a retreating glacier
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
Landform
Processes
involved
Description
1 other fact
Example
Homework
• Textbook page 160
• Questions 7 - 12
Exam Questions
• Long Q’s;Choice between fluvial / coastal /
mass movement / glacial...
• Long Q’s; OS Map / Aerial Photograph
• Short Q’s; Variety of questions on glacial
landforms.
Exam Questions