Earth Science, 12e

1. Earth Science, 12e Glaciers, Deserts, and WindChapter 6

2. Glaciers: a part of two basic cycles in the Earth system • Glaciers are a part of both the hydrologic cycle and rock cycle • Glacier – a thick mass of ice that forms over land from the compaction and recrystallization of snow and shows evidence of past or present flow

3. Glaciers: a part of two basic cycles in the Earth system • Types of glaciers • Valley, or alpine glaciers – form in mountainous areas • Ice sheets, or continental glaciers • Large scale • e.g., Over Greenland and Antarctica • Other types • Ice caps and piedmont glaciers

4. Currently ice sheets cover Greenland and Antarctica Figure 6.2

5. Glaciers: a part of two basic cycles in the Earth system • Movement of glacial ice • Types of glacial movements • Plastic flow • Slipping along the ground • Zone of fracture • Uppermost 50 meters • Crevasses form in brittle ice

6. Glaciers: a part of two basic cycles in the Earth system • Movement of glacial ice • Zone of accumulation – the area where a glacier forms • Zone of wastage – the area where there is a net loss due to melting

7. The glacial budget Figure 6.7

8. Glaciers: a part of two basic cycles in the Earth system • Glaciers erode by • Plucking – lifting of rock blocks • Abrasion • Rock flour (pulverized rock) • Striations (grooves in the bedrock)

9. Glaciers: a part of two basic cycles in the Earth system • Landforms created by glacial erosion • Glacial trough • Hanging valley • Cirque • Arête • Horn • Fiord

10. Erosional landforms created by alpine glaciers Figure 6.10 C

11. The Matterhorn in the Swiss Alps Figure 6.12

12. Glaciers: a part of two basic cycles in the Earth system • Glacial deposits • Glacial drift • All sediments of glacial origin • Types of glacial drift • Till – material that is deposited directly by ice • Stratified drift – sediment deposited by meltwater

13. Glacial till is typically unstratified and unsorted Figure 6.13

14. Close-up view of the boulder in the previous slide

15. Glaciers: a part of two basic cycles in the Earth system • Glacial deposits • Depositional features • Moraines– layers or ridges of till • Types of moraines • Lateral • Medial • End • Ground

16. Glaciers: a part of two basic cycles in the Earth system • Glacial deposits • Depositional features • Outwash plain, or valley train • Kettles • Drumlins • Eskers • Kames

17. Glacial depositional features Figure 6.18

18. Kettle lakes Figure 6.18

19. Glaciers: a part of two basic cycles in the Earth system • Glaciers of the past • Ice Age • Began 2 to 3 million years ago • Division of geological time is called the Pleistocene epoch • Ice covered 30% of Earth’s land area

20. Maximum extent of ice during the Ice Age Figure 6.22

21. Glaciers: a part of two basic cycles in the Earth system • Glaciers of the past • Indirect effects of Ice Age glaciers • Migration of animals and plants • Rebounding upward of the crust • Worldwide change in sea level • Climatic changes

22. Glaciers: a part of two basic cycles in the Earth system • Causes of glaciation • Successful theory must account for • Cooling of Earth, as well as • Short-term climatic changes • Proposed possible causes • Plate tectonics • Continents were arranged differently • Changes in oceanic circulation

23. Glaciers: a part of two basic cycles in the Earth system • Causes of glaciation • Proposed possible causes • Variations in Earth’s orbit • Milankovitch hypothesis • Shape (eccentricity) of Earth’s orbit varies • Angle of Earth’s axis (obliquity) changes • Axis wobbles (precession) • Changes in climate over the past several hundred thousand years are closely associated with variations in Earth’s orbit

24. Deserts • Geologic processes in arid climates • Weathering • Not as effective as in humid regions • Mechanical weathering forms unaltered rock and mineral fragments • Some chemical weathering does occur • Clay forms • Thin soil forms

25. Deserts • Geologic processes in arid climates • Role of water in arid climates • Streams are dry most of the time • Desert streams are said to be ephemeral • Flow only during periods of rainfall • Different names are used for desert streams including wash, arroyo, wadi, donga, and nullah

26. Deserts • Geologic processes in arid climates • Role of water in arid climates • Desert rainfall • Rain often occurs as heavy showers • Causes flash floods • Poorly integrated drainage • Most erosional work in a desert is done by running water

27. A dry stream channel in the desert Figure 6.28 A

28. The same stream channel following heavy rainfall Figure 6.28 B

29. Deserts • Basin and Range: the evolution of a desert landscape • Uplifted crustal blocks • Interior drainage into basins produces • Alluvial fans and bajadas • Playas and playa lakes

30. Deserts • Basin and Range: the evolution of a desert landscape • Erosion of mountain mass causes local relief to continually diminish • Eventually mountains are reduced to a few large bedrock knobs called inselbergs projecting above a sediment-filled basin

31. Landscape evolution in a mountainous desert – early Figure 6.29 A

32. Landscape evolution in a mountainous desert – middle Figure 6.29 B

33. Landscape evolution in a mountainous desert – late Figure 6.29 C

34. Deserts • Wind erosion • Deflation • Lifting of loose material • Produces • Blowouts • Desert pavement • Abrasion

35. Formation of desert pavement Figure 6.34

36. Deserts • Types of wind deposits • Loess • Deposits of windblown silt • Extensive blanket deposits • Primary sources are deserts and glacial stratified drift

37. Deserts • Types of wind deposits • Sand dunes • Mounds and ridges of sand formed from the wind’s bed load • Characteristic features • Slip face – the leeward slope of the dune • Cross beds – sloping layers of sand in the dune

38. Formation of sand dunes Figure 6.37

39. Deserts • Types of wind deposits • Sand dunes • Types of sand dunes • Barchan dunes • Transverse dunes • Longitudinal dunes • Parabolic dunes • Star dunes

40. Sand dune types Figure 6.38

41. Sand dunes in the western United States