Topic 2: Frozen Water

1. Topic 2: Frozen Water Grade 8 Science

2. Distribution of water on earth Groundwater = 0.63% Rivers/Lakes/Ponds = 0.02% Glaciers/Ice sheets = 2.15% Oceans / Seas = 97.02%

3. Distribution of Water:

4. Ice is the second largest deposit of water on earth after ocean. • It covers ~10% of the earth’s land. • Snow can build up so high that the lower levels are compressed into ice. The pressure on the ice eventually causes it to melt and slide down the hill. • A glacier is a moving mass of ice and snow. • An ice cap is a glacier that forms on an extensive area of relatively level land and so it just flows out from the center. • An ice field is an upland area of ice that feeds two or more glaciers.

6. Valley glaciers are glaciers that exist in a mountain range. • Temperature stays low enough year round for them to continue to grow and creep along. • Continental glaciers are huge masses of ice and snow. • So thick they can burry mountain ranges. • Antarctica is covered by continental glaciers that spread out over 932 000km2. • An icefall results from a glacier flowing over a cliff and breaking up. Athabasca Glacier

7. A crevasse is a fissure or crack in the ice. • Glaciers flow downhill spreading out as they go. • They take the shape of the rock they go over and flow away from areas of accumulation.

8. A retreating glacier looks like it is flowing uphill even though it is still actually flowing downhill. • This occurs when the ice melts faster than it is replaced. This causes the glacier to shorten and retreat. • Glaciers can also do the opposite process and be known as advancing glaciers. Athabasca Glacier, Jasper National Park

9. Pack Ice & Icebergs • Pack ice is a sheet of ice rarely more than 5m thick. • It breaks easily. • Formed from freezing seawater. • Icebergs are large chunks of ice that calve (break loose) from continental glaciers and flow into the ocean. • They can be several km long and 100m high. • The tops melt faster from the sun and wind.

10. As they move, glaciers push any loose materials aside. • Eroded sediments pile up along the sides. • Water flows into rock cracks, refreezes and expands splitting the rock and carrying pieces away. This catches the boulders, gravel, and sand.

11. The new material scrapes the bottoms and side causing scars or scratches in the rocks called striations. • Cirques are bowl shaped basins in sides of mountains caused by glacier erosion.

12. Glacial Products • The ridge of till at the end of the glacier is piled up and looks like a big ridge. This is called a moraine. • Outwash is material deposited by the water of a melted glacier. • A winding ridge of sand and gravel can be left behind which is known as an esker. • Meltwater is water formed by the melting of snow and ice. • Can carve a path through a glacier. • meltwater

13. A millwell is the name of the deep track carved through the glacier • Ice fields, glaciers, and year round snow act as natural reservoirs. • They gradually release reserved water in the summer. • They slow the passage of water through the water cycle. • They release water when it is needed most; hot dry weather.

14. Earth has had at least seven ice ages during the last several million years. • Ice ages are periods of major cooling. • The last one started 120 000 years ago and lasted for 109 000 years. • Glaciers covered 28% of the land.

15. Ice Ages • It is hypothesized that ice ages happen because of: 1. A reduction of thermal energy given off by the sun. 2. Increased dust in the atmosphere from volcanic activity reduces the suns energy hitting the earth. 3. Increased mountain formation holds snow that reflects sunlight to reduce earth’s temperature. 4. Movement of tectonic plates prevents ocean currents from mixing hot and cold regions. 5. Change of the earth’s axis or tilt facing the sun.