Glaciers

1. Glaciers

2. How do chunks of ice break off from a glacier? • Changing temperatures may cause ice to cleave from the glacier in large chunks called icebergs.

3. How and why do scientists study glacial ice? • They track glacial movement to determine climate trends • They analyze the composition of the ice to delve into Earth’s history

4. Topic Preview: • What is a glacier? • Glacial Movement and erosion • Glacial Deposits • Ice Ages

5. What Is a Glacier? • Glaciers are huge masses of ice that move under the influence of gravity. • They form from compacted and recrystallized snow.

6. Glaciers comprise about 75% of the Earth’s water. They form in regions that are always covered with snow. The snow line is the lowest elevation at which a permanent layer of snow occurs in the summer. Snow Line: In areas close to the equator, the snow line elevation is high and lowers as we move farther away from the equator.

7. Glacial Formation: • Glaciers form in snow fields when buried snow is compressed and recrystalized to form firn [rough granular ice material] • As firn thickens, its lower layers become more compressed and form solid layers of ice. • The ice flows under the weight of the overlying layers and begins, becoming a glacier.

8. Valley Glaciers: Moves within valley walls. Forms in the valley of a high mountain range and flows downhill. Varies in size from several meters to several hundred meters. Continental Glaciers: Forms inland in polar regions Moves outward in all directions to lower elevations Circular or oval in shape and much thicker than a valley glacier. There are two main types of glaciers:

9. What is a glacier? Let’s review . . . • Much of Earth’s fresh water is frozen in valley glaciers or continental glaciers. • Glaciers form above the snow line from compressed snow called firn. • The snow line elevation is high in areas close to the equator and gets lower in areas farther from the equator.

10. Glacial Movement and Erosion • Glaciers move by the processes of basal slip and plastic flow • Basal Slip: Reduction of friction as a result of melting ice. Occurs along the glacier’s base. • Plastic Flow: Materials in the lower/central portion of the glacier change shape constantly due to the overlying pressure and slip past each other, creating forward movement [Think ‘silly puddy’]

11. Glacial Features: • Crevasses: • Cracks that form across the width of a glacier • Form because ice near the surface is more rigid than ice near the center and snaps under pressure. • Usually no more than 50 meters deep.

12. Ice Front: • The end or forward moving part of the glacier. • Cold seasons trigger an advance • Warm seasons trigger recession.

13. Icebergs: • Calving occurs when the snow line is at or close to sea level and large chunks of the glacier shear off and fall into the sea forming icebergs.

14. Glacial Movement Review . . . • Gravity causes glaciers to move • The glacier’s ice front either advances or retreats, depending on conditions • If a glacier’s ice front is near the sea, icebergs may break off and fall into the sea by calving from the main glacier.

15. As glaciers move, they erode rock materials in ways that alter the landscape. Sediment can be carried either on top, in, or under the glacier. The unsorted material carried in a glacier is called till. Moraines form from the accumulation of glacial till. Glacial Erosion:

16. Striations can show the general direction the glacier was traveling. • Striations form when materials carried along the bottom of a glacier [coarse sand, pebbles, sharp boulders, etc.] leave long, parallel scratches on the rocks they pass over.

17. Valley glaciers erode valley walls and floors to create u-shape glacial valleys and steep, jagged formations. They sharpen mountain peaks by eroding the sides. Valley glaciers form: Cirques: A basin at the head of a valley glacier, can fill with water when the glacier melts. Arete: Sharp ridge between two cirques. Erosion by Valley Glaciers:

18. Mt. Ranier Valley Glacier

19. Erosion by Continental Glaciers: • Continental glaciers grind down mountain peaks and leave them polished and rounded.

20. When glaciers retreat, they deposit materials in characteristic features that alter the landscape. Till: Unsorted material deposited directly by the ice. Outwash: Sorted materials deposited by glacial meltwater. Glacial Deposition:

21. Moraines are deposits of glacial till left along the path of the glacier. • They can be . . . • Lateral [sides] • Medial [middle] • Terminal [end]

22. Drumlins: Long, canoe shaped hills, generally found in groups. Form when glaciers pass over deposits of glacial till like moraines. • [see page 200]

23. Kettle: Bowl-like hollow in an outwash which occurs when large blocks of glacial ice melt. Kettle Lakes form when they fill with water Eskers: Long winding ridges formed when sand and gravel fill meltwater tunnels within glaciers.

24. Kame: Cone-shaped deposit of till formed at the front of a glacier from runoff of the surface. Outwash Plain: Overlapping areas of glacial outwash similar to alluvial fans.

25. Glacial Deposition Review . . . • When glaciers retreat, they leave behind deposits. • Till is unsorted, unstratified material deposited directly by the ice. • Outwash is sorted, stratified material deposited by meltwater. • Examples of glacial deposition are drumlins, eskers, moraines, kames and erratics.

26. Ice Age • An Ice Age is classified as an extensive period of glaciation.

27. Earth has experienced ice ages in its past The most recent ice age occurred about 11,000 years ago and is responsible for the formation of the great lakes in Michigan and Canada. Ice ages occur as a result of changes in The position of the Earth in relation to the sun. CO2 levels in the atmosphere. Positions of Earth’s landmasses. Amount of solar energy reaching the Earth’s surface.

28. What, you wanted more?? TOO BAD!! It’s over. The End!!!!