1. Glaciers
Chapter 8, Section 2

2. How Glaciers Form and Move
What is a glacier?
Large mass of snow and ice that moves on land under its own weight.

3. How Glaciers Form and Move
Formation of Glaciers
Snow stays on the ground year-round.
Increasing weight of newer layers on top compress the bottom layers into ice.
When the force become large enough, the lower layers become plastic-like and begin to move.

4. Ice Eroding Rock Erosion and Deposition
As glaciers move, they erode the land underneath them and carry the material elsewhere.

5. Ice Eroding Rock Plucking
Glacial ice melts and flows into cracks in rocks.
Water in the cracks freezes and expands.
The rock becomes fractured.
Pieces of the rock are lifted out by the moving glacier, resulting in boulders, gravel, and sand being added to the bottom and sides of the glacier.

6. Ice Eroding Rock Transporting
Glaciers can transport large volumes of sediment and rock.

7. Ice Eroding Rock Scouring
As glaciers move, the plucked rock fragments carried in the glacier scrape and scour the soil and bedrock over which the glacier travels.
Grooves
Deep, long, parallel scars on rocks.
Striations
More shallow scars.
Grooves and striations indicate the direction a glacier was traveling.

8. Ice Depositing Sediments
Melting Glaciers
As glaciers melt, they begin to shrink or retreat.
As the glacier retreats, it cannot carry as much sediment so the sediment is deposited.

9. Ice Depositing Sediments
Till
Unsorted mixture of boulders, sand, clay, and silt left behind by a retreating glacier.
Can cover huge areas of land (enough to fill in whole valleys).

10. Ice Depositing Sediments
Moraine Deposits
Till that is deposited at the end and sides of a moving glacier.
Occurs because rocks and soil are moved to the ends of the glacier (like groceries piling up at the end of a conveyor belt).

11. Ice Depositing Sediments
Outwash Deposit
Material that is carried by melting water from the glacier and then deposited in layers beyond the end of the glacier.
Heavier sediments are deposited first and so are closer to the glacier.
Fan-shaped deposits (like at the mouth of a river) can also form.

12. Ice Depositing Sediments
Eskers
Long winding ridge of till.
Forms in a melting glacier when meltwater forms a river within the ice.
The river carries sand and gravel which are deposited within the river channel.

13. Continental Glaciers Continental Glaciers Huge masses of ice and snow.
Can be thicker than some mountain ranges.
Cover only 10% of the Earth.
Mostly located near the poles in Antarctica and Greenland.

14. Continental Glaciers Climate Changes
Extensive glaciers have covered large portions of the Earth many times over the last 2 to 3 million years.
These periods are known as ice ages.
Average air temperature was about 5 degrees Celsius colder than today.
Continental glaciers covered as much as 28% of the surface of the Earth.
The last ice age hit its maximum extent about 18,000 years ago.

15. Valley Glaciers Valley Glaciers
Form in high mountains where snow does not melt in the summer.

16. Valley Glaciers Evidence of Valley Glaciers Striations Plucking
Cirques
Bowl-shaped basins eroded into the side of the mountain by a valley glacier.
Arête
Long ridge eroded between two valley glaciers.
Horn
Sharp peak eroded by many valley glaciers.
U-shaped Valleys
(Streams and rivers form V-shaped valleys.)

18. Importance of Glaciers
Affects of Glaciers
Greatly change the landscape of the Earth.
Leave behind economically important sediments such as sand and gravel deposits