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Glacial Erosion. 1. Rocks frozen into glacier ice. Ice. 2. Glacier moves. Valley Floor. 3. Rocks scrape along the valley floor and erode it. This type of erosion is called abrasion. Glacial Erosion. 1. Ice freezes around bits of rock.

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slide1

Glacial Erosion

1. Rocks frozen into glacier ice.

Ice

2. Glacier moves

Valley Floor

3. Rocks scrape along the valley floor and erode it.

This type of erosion is called abrasion.

glacial erosion
Glacial Erosion

1. Ice freezes around bits of rock

3. Bits of rock are taken from the rock face with the ice

Ice

2. The Glacier moves

Rock

This type of erosion is called plucking

formation of a corrie
Formation of a Corrie

How to answer the question:

‘Explain how a corrie was formed.’

  • Mention what the shape was like before
  • Mention what the shape is like afterwards
  • Mention how the shape was changed
before glaciation
Before Glaciation
  • Snow falls in a hollow high in the mountains
  • The snow compresses into ice
during glaciation
During Glaciation
  • The ice moves downhill as a glacier
  • At ‘A’ freeze thaw weathering makes the backwall steeper and jagged

A

B

  • At ‘B’ plucking makes the backwall steeper and jagged

C

  • At ‘C’ abrasion deepens and smoothes the hollow

For full credit marks mention how abrasion, plucking & freeze thaw work

after glaciation
After Glaciation
  • The corrie has steep sides and steep back wall
  • The hollow is deeper
  • The lip is emphasised by moraine deposited by the glacier
  • Often water fills the corrie known as a tarn
slide7

formation of an arete

  • Two Glaciers erode back to back into a mountain by plucking as they move downhill.
  • This forms 2 corries.
  • Plucking makes the ridge narrower and this is called an Arete.
  • Freeze-thaw weathering makes the Arete sharper
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Where glaciers start in a hollow they move downhill and erode by plucking and abrasion to form corries.

  • Three or more corries form back to back or side by side
  • Where the corrie sidewalls meet they form ridges which become narrower by plucking.
  • These are called Aretes. Three Arêtes meet to form a pyramidal peak
  • The peak becomes sharper by freeze-thaw weathering

formation of a pyramidal peak

slide9

Formation of U-shaped valley

Before glaciation a v-shaped valley

During the ice age a glacier moves down the valley.

Rocks trapped in the bottom of the ice act like sandpaper wearing away the valley by abrasion.

The glacier deepens, straightens and widens the valley by abrasion.

After the ice melts a U-Shaped valley remains

After Glaciation there is sometimes a mis-fit stream or ribbon lake in the bottom of the valley

slide10

hanging valley

  • Erosion in the main glacier is far greater making a deeper valley.
  • Erosion in the tributary glaciers is less making a shallower valley.
  • The shallower valleys are left ‘hanging’ above the deeper main valley.
  • 4. Waterfalls often fall over the edge at the end of the hanging valley into the main valley.
  • 5. At the base of a waterfall alluvial fans are sometimes found as a result of deposition

Map View

Tributary valley

Main valley

Cross Section

Main valley

Tributary valley

ribbon lakes
Ribbon Lakes
  • Glaciers move down a former v-shaped valley and erode the valley by abrasion and plucking turning the valley into a u-shape.
  • Some ribbon lakes form when the glacier meets softer rock.
  • The glacier erodes more deeply at these points.
  • After the glacier has melted the deeper parts fill with water to form ribbon lakes

Ribbon Lake

Hard Rock

Hard Rock

Hard Rock

Hard Rock

Soft Rock

Soft Rock

Side view of valley before Glaciation

Side view of valley after Glaciation

how till is formed
How Till is formed
  • The temperature rises due to climate change at the end of the ice age or the temperature rises as the glacier reaches lower land.
  • The glacier begins to melt. The snout moves back up the valley.
  • The melting ice cannot hold the rocks, gravel and sand that have been trapped in it.
  • All this material is deposited as the glacier continues to melt.
  • The moraine is all mixed up with different sizes of material.
  • Where the glacier has been it leaves behind moraine on the floor of the valley called ground moraine, till or boulder clay.

Terminal Moraine

Drumlins

Melting Glacier

Till

Outwash Plain

how drumlins are formed
How Drumlins are formed
  • The temperature rises due to climate change at the end of the ice age.
  • The glacier begins to melt. The snout moves back up the valley.
  • The melting ice cannot hold the rocks, gravel and sand that have been trapped in it.
  • All this material is deposited as the glacier continues to melt.
  • The moraine is all mixed up with different sizes of material.
  • A large rock is deposited and traps more moraine around it forming a drumlin
  • The glacier continues to move when it is melting and makes the drumlin smooth

Terminal Moraine

Drumlins

Melting Glacier

Till

Outwash Plain

how terminal moraine is formed
How Terminal Moraine is formed
  • The glacier pushes the moraine in front of it like a bulldozer
  • The temperature rises due to climate change at the end of the ice age.
  • The glacier begins to melt. The snout moves back up the valley.
  • The melting ice cannot hold the rocks, gravel and sand that have been trapped in it.
  • All this material is deposited as the glacier continues to melt.
  • The moraine is all mixed up with different sizes of material
  • The furthest point the glacier reached is marked by a ridge of material running across the valley called terminal moraine

Terminal Moraine

Terminal Moraine

Drumlins

Melting Glacier

Melting Glacier

Till

Till

Outwash Plain

Outwash Plain

how the outwash plain is formed
How the outwash plain is formed
  • The temperature rises due to climate change at the end of the ice age.
  • The glacier begins to melt. The snout moves back up the valley and melt-water streams carry material down the valley.
  • The outwash plain is in front of where the glacier has been and is deposited by melt-water.
  • The outwash plain is made from sorted sands and gravels.
  • Gravels are deposited in the spring when there is more melting. Sands are deposited in the autumn when there is less melting

Drumlins

Melting Glacier

Till

Outwash Plain

Terminal Moraine

how an esker is formed
How an esker is formed
  • The temperature rises due to climate change at the end of the ice age.
  • The glacier begins to melt.
  • Tunnels form in the melting ice
  • Meltwater streams flow in the tunnels
  • Deposits are laid down along the course of where the stream has been.
  • The snout moves back up the valley
  • Long, winding ridges of sorted material known as eskers are left where these streams have been
  • Gravels are deposited in the spring when there is more melting. Sands are deposited in the autumn when there is less melting
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