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Edward J. Tarbuck & Frederick K. Lutgens

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1 Edward J. Tarbuck & Frederick K. Lutgens
Earth Science, 10e Edward J. Tarbuck & Frederick K. Lutgens

2 Glaciers, Deserts, and Wind Chapter 5
Earth Science, 10e Stan Hatfield and Ken Pinzke Southwestern Illinois College

3 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

4 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

5 Currently continental ice sheets cover Greenland and Antarctica

6 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

7 Glaciers move by basal sliding and internal plastic flow

8 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

9 The glacial budget

10 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)

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

12 Erosional landforms created by alpine glaciers

13 The Matterhorn in the Swiss Alps

14 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

15 Glacial till is typically unstratified and unsorted

16 Close-up view of the boulder in the previous slide

17 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

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

19 Glacial depositional features

20 A drumlin in upstate New York

21 Kettle lakes

22 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

23 Maximum extent of ice during the Ice Age

24 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

25 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

26 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

27 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

28 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

29 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

30 A dry stream channel in the desert

31 The same stream channel following heavy rainfall

32 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

33 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

34 Landscape evolution in a mountainous desert – early stage

35 Landscape evolution in a mountainous desert – middle stage

36 Landscape evolution in a mountainous desert – late stage

37 Inselbergs in southern California

38 Deserts Wind erosion Deflation Abrasion Lifting of loose material
Produces Blowouts Desert pavement Abrasion

39 Formation of a desert blowout

40 Formation of desert pavement

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

42 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

43 Formation of sand dunes

44 Deserts Types of wind deposits Sand dunes Types of sand dunes
Barchan dunes Transverse dunes Longitudinal dunes Parabolic dunes Star dunes

45 Sand dune types

46 Sand dunes in the western United States

47 End of Chapter 5


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