1. Earth Science -
Glaciers & Ice Ages

2. Davidson Glacier near Haines, Alaska

3. Glaciers
Glacier: a large, long-lasting mass of ice, formed on land that moves under the influence of gravity and its own weight
Glaciers form by accumulation and compaction of snow
Packed snow becomes firn
Then refreezes to ice

4. Formation of Glacial Ice from Snow

5. Glaciation Types Alpine Glaciation: found in mountainous regions
Continental Glaciation: exists where a large part of a continent is covered by glacial ice - cover vast areas

6. Types of Glaciers

7. Alpine Glaciers Are confined by surrounding mountains Types:
Cirque Glaciers – erode basins in mountainsides
Valley Glaciers – flow into preexisting stream valleys
Icecaps – form on mountaintops

8. Types of Glaciers– Cirque Glacier
Mount Edith Cavell, Jasper National Park, Canada

9. Types of Glaciers – Valley Glacier
Tongas National Forest, Alaska

10. Types of Glaciers – Icecap and Continental
Sentinal Range, Antarctica

11. A Glacier’s Budget A story of gains and losses
Gain snow in zone of accumulation
Lose ice in zone of ablation
Budget can be:
Positive (growth)
Static (unchanging)
Negative (net melting)

12. A Glacier’s Budget Year round Snow Summer Rain
Note that a glacier is a river. Even if the terminus doesn’t advance, still flows

13. Iceberg Calving – Hubbard Glacier, Wrangell-St
Iceberg Calving – Hubbard Glacier, Wrangell-St. Elias National Park, Alaska

14. Erosion by Glaciers Abrasion Quarrying
Rocks embedded in glacier’s base make linear scratches and grooves in bedrock
Quarrying
Glacier breaks off and removes large blocks of rock

15. Glacial Abrasion in Bedrock
Source: Tom Bean

16. Glacial Erosion – Roche Moutonee
Yosemite NP, California

17. Erosion by Glaciers (cont)
Alpine glaciers erode mountain slopes into horseshoe shaped basins called cirques
Erosion of multiple cirques erodes intervening rock, causing:
Horns: pointy peaks
Aretes: long serrated ridges
Cols: passes through the ridges.

18. Alpine Glacial Erosion

19. Alpine Glacial Erosion
Origin of Hanging Valley

20. Yosemite Falls

21. Valley Glaciers Erode a large quantity of bedrock and sediment
Convert V-shaped stream valleys into U-shaped glacial valleys.

22. U-Shaped Valley in Tracy Wilderness, Southeastern Alaska

23. Seawater Flooded U-Shaped Valleys: Fjords
Bela Bela Fjord, BC

24. Erosion by Continental Glaciation
Erosional Landforms much larger in scale than alpine glaciers
Huge U-shaped troughs, including:
Finger Lakes, Great Lakes, Puget Sound,
and Loch Ness were all once valleys
excavated by glaciers

25. Erosion of Preglacial Lowlands (Finger Lakes)

26. Erosion of Preglacial Lowlands (Great Lakes of North America)
Source: U.S. Dept. of Interior, USGS Eros Date Center

27. Glacial Deposits or Drift
Glacial Till: unsorted, unstratified sediments deposited by melting ice.
May contain glacial erratics
Often accumulate at glacier’s terminus as a Moraine: hills of sediment left by a glacier’s retreat.

28. Advance & Retreat: Moraines

29. Large Granite Erratics

30. Medial Moraines – Kennicott Glacier

31. Effects of Glaciation Change Climate – increased precipitation
Drop in sea-level: alter coastlines
Form continent-wide Dams
Divert streams – Ohio and Missouri rivers

32. Lowered Sea-level - Landbridge

33. Lowered Sea-level exposed continental shelf

34. Giant Ripples of the Missoula Flooding

35. Causes of Ice Ages Plate Tectonics Moves Continents to Poles
Raises mountains above snowline
Orbit Distances, Axis Tilt and Wobble
Moderates solar radiation past 65° N
Croll-Milankovitch Cycles ~ 100,000 years
Low summertime radiation causes glaciers to expand

36. Glacier Distribution 20,000 ya
Approximate Maximum

37. Milankovitch Cycles
100,000 years

38. 41,000 years

39. Earth’s Past Ice Ages PreCambrian Glaciation
750 mya ice flowed from poles to tropics
Late Pennsylvanian & Permian Glaciation
covered South Africa, South America, India, Australia
Pleistocene Glaciation
most recent, ended about 10,000 years ago

40. Pleistocene Glaciation
started 1.6 mya -30 advances and retreats
Latest retreat ended 10,000 years ago
“Little Ice Age” occurred 700 to 150 years ago, paralyzed Europe
Next glaciation period - ???

41. Sustained warming since 1850
Athabaska Glacier, Columbia Icefield, W. Canada

42. End of Glaciers