Glaciers and Ice Ages

1. Glaciers and Ice Ages By: Caitlin McNeal Pete Buscemi Pat Carriglio (Group 10)

2. Sec. 13.1-Formation of Glaciers • Definition of Glacier: - massive, long lasting, moving mass of compacted snow and ice. • Glaciers form in two environments. Alpine glaciers form at all latitudes on high, snowy mountains. Continental ice sheets form at all elevations in the cold polar regions.

3. Alpine glaciers form in summits were winter snowfall is deep and summers are short and cool. The growth of an alpine glacier depends on both temperature and precipitation. Alpine Glaciers

4. Continental Glaciers form in areas that have winters that are so long and cold and summers are short and cool in polar regions that glaciers cover most of the land regardless of its elevation. The Antarctic Ice Sheet covers about 13 million square kilometers, an area almost 1.5 times the size of the U.S. It blankets entire mountain ranges and the mountains that rise above its surface. Continental Glaciers

5. 13.2 – Glacial Movement • Glaciers move by two mechanisms: 1. Basal Slip and 2. Plastic Flow • BS= glacier sliding over bedrock. • PF= ice flows as a viscous fluid.

6. The Mass Balance of a Glacier • The higher level part of the glacier is called the zone of accumulation. • The lower level part of a glacier is called the zone of ablation. • The snow line is the boundary between permanent snow and seasonal snow. • Glaciers tend to grow and shrink based on location and temperatures.

7. Icebergs • Icebergs: giant chunks of ice that break off of glaciers. • The largest icebergs in the world are those that break away from the Antarctic ice shelf. • The tallest icebergs break away from tidewater glaciers in Greenland.

8. Glacial Erosion Glaciers erode and transport huge quantities of rocks and sediment. Glacial Striations- Rocks embedded in the ice scrape across bedrock, cutting deep, parallel grooves and scratches.

9. Erosional Landforms created by Alpine Glaciers • A glacier is not confined to a narrow stream bed but instead fills its entire valley. • As a result, it scours the sides of the valley as well as the bottom, carving a broad, rounded, U-shaped valley.

10. Erosional Landforms created by Alpine Glaciers cont….. • A Cirque is a steep cliff that drops off into a horse-shoe-shape into the mountain side. • A cirque forms by snow accumulates and glacier form, the ice flows down the mountain side. As time goes on, the glacier carries rocks to the lower part of the valleys.

11. Erosional Landforms created by Alpine Glaciers cont….. • Tarn- a small lake formed by a glacier melting at the base of the cirque. • Pasternoster Lakes- A series of lakes which are commonly connected by rapids and waterfalls.

12. Glacial Deposits • Drift- All rocks or sediment transported and deposited by a glacier. • Drift is divided into two categories 1. Till – Deposited directly by glacial ice 2. Stratified drift – first carried by glaciers and then transported and deposited by a stream.

13. Moraines • Moraine – a mound or ridge of till • End Moraine – sediment accumulates at the terminus to form a ridge • Dirty, old ice forms at the bottom and clean snow lies higher up.

14. Drumlins • Drumlins- Elongate hills, that cover parts of the northern United States • Typically, 1-2 kilometers long and about 15-50 meters high.

15. “Snowball Earth” • “At least twice, possibly as many as five times, between 750 and 580 million years ago, massive ice sheets completely covered all continents, even at the equator, entombing the entire globe in a one kilometer thick shell of ice.”

16. Evidence For “Snowball Earth” • Tillite • hard, solid rock that is in every other respect resembles the Pleistocene tills • deposited so long ago that it has been cemented into hard rock • at least two thick layers of tillite between 750 and 580 million years old on almost every continent • Some continents lay at the equator when tillite was formed

17. Evidence Against “Snowball Earth” • Contrasts with Pleistocene Ice Age completely frozen polar seas and ice on 1/3 of the continents • Carbon dioxide in the atmosphere was too high to permit radical global cooling, like Snowball Earth’s theory presents

18. Why didn’t the Earth stay frozen forever? • Carbon dioxide in the atmosphere would have melted the ice • Eventual Greenhouse Effect because of volcanoes on sea floor • Last thaw occurred about 580 million years ago, about the same time multicellular life bloomed • “ecologic habitats ready to be colonized • Newly warmed Earth • Plants and animals multiplied • Abundant sources of food

19. Disappearing Glaciers • Most glacier loss in the 1990’s, the warmest decade in history • Due to an increase in atmospheric carbon dioxide • First sign of human-caused global warming • Alpine glaciers reflect this in a highly visible way • Glacier National Park in Montana glaciers have shrunk by about a third as a group since 1850 (many glaciers have disappeared completely!) • In about thirty years, there could be ZERO glaciers in Glacier National Park, if they continue disappearing at this pace

20. A bit about global warming… • Global climate changes do not occur uniformly around the world • North Pole regions are warming faster than the average for the Earth as a whole • Ice Shelves • Thick masses of ice that are floating in the ocean, but are connected to glaciers on land • Located mostly around Antarctica • Respond to temperature change (i.e. global warming) more sensitively than glaciers

21. http://www.arjen.com/travel/kenya_tanzania/20030926_118.jpg • Mt Kenya, Kenya: lost 92% of it’s mass in the last 100 years. • Caucasus Mountains, Russia: 50% less since the early 1900’s. • Duosuogang Peak, China: shrunk by some 60% since 1970’s.

22. Sources http://www.arjen.com/travel/kenya_tanzania/20030926_118.jpg