1. Chapter 8 Erosional Forces Section 8-2 Glaciers Note Guide

2. How Glaciers Move and Form ► Snow remains on the ground year-round in some areas of the world. ► As snow piles up, the weight increases and it compresses the lower layers into ice. ► The pressure makes the ice plastic like, so the mass begins to flow and move away from its source. ► The pressure makes the ice plastic like, so the mass begins to flow and move away from its source. ► A large mass of ice and snow moving on land under its own weight is a glacier.

3. An Advancing Glacier!

4. A glacier that has retreated!

5. Ice Eroding Rock ► Glaciers are agents of Erosion. ► As glaciers move along the surface of the Earth, they pick up eroded material and deposit it somewhere else. ► When glacial ice melts, water flows into the cracks of rocks. When the water freezes, it expands and fractures the rock. ► The pieces of rock are lifted out by the ice. This process is called plucking.

6. Ice Eroding Rock ► Plucking results in boulders, gravel, and sand being added to the bottom of glaciers. ► Plucked rock fragments and sand at the bottom of a glacier scrape and scour the soil and bedrock on Earth’s surface and erode the ground.  Deep, long, parallel scars called grooves are left behind by rock fragments.  Shallower marks on the bedrock are called striations ► Both of these indicate the direction the glacier moved.

7. Plucking!

8. Striations

9. Ice Depositing Sediment ► When glaciers begin to melt, they deposit sediment on land. ► When a glacier melts and shrinks back, it is said to retreat. ► As it retreats, it leaves a jumble of boulders, sand, silt and clay behind. ► This is called glacial till.

10. Ice Depositing Sediment ► Till is also deposited at the end of a glacier when it is not moving. ► Rocks and soil are moved to the end of the glacier and piles up in a big ridge. ► This ridge is called a moraine.  Moraines are also deposited along the sides of a glacier.

11. Moraine

12. Till

13. Outwash and Till

14. Ice Depositing Sediment ► In a melting glacier, meltwater forms a stream within the ice. ► This river carries sand and gravel and deposits them within its channel. ► When the glacier melts, a winding ridge of sand and gravel is left behind. ► This is called an esker.

15. Esker!

16. 2 Types of Glaciers ► Continental glaciers cover 10% of the Earth, mostly near Antarctica and Greenland. ► The continental glaciers are huge masses of Ice and snow, and are thicker than some Mountain ranges.  In the past, continental glaciers covered as much as 28 % of Earth. The periods of widespread glaciations are known as Ice ages.

17. 2 Types of Glaciers ► Valley glaciers occur today in high mountains where the average temperature is low enough to prevent snow from melting in the summer  Evidence that valley glaciers existed in the mountains includes striations or evidence of plucking from the top of a mountain where the glacier was in contact with solid rock.  Valley glaciers erode curved, bowl- shaped basins, called cirques into the sides of mountains.

18. 2 Types of Glaciers  If two valley glaciers side by side erode a mountain, then a long ridge called an Arête forms between them.  If valley glaciers erode a mountain from several directions, a horn might form.

19. 2 Types of Glaciers ► To tell the difference between valleys that have been eroded by glaciers or those that have been eroded by streams: ► Valleys that have been eroded by glaciers are U -shaped.  Valleys that have been eroded by streams are V - shaped. ► Glaciers are important because they change the Earth’s surface and they have left behind sediments that are important resources.

20. Valley Glacier

21. Valley Glacier Erosion

22. Glacier Coverage!