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Glaciers, Deserts, and Wind Chapter 6
Earth Science, 12e Glaciers, Deserts, and Wind Chapter 6
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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
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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
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Currently ice sheets cover Greenland and Antarctica
Figure 6.2
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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
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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
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The glacial budget Figure 6.7
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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)
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Glaciers: a part of two basic cycles in the Earth system
Landforms created by glacial erosion Glacial trough Hanging valley Cirque Arête Horn Fiord
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Erosional landforms created by alpine glaciers
Figure 6.10 C
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The Matterhorn in the Swiss Alps
Figure 6.12
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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
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Glacial till is typically unstratified and unsorted
Figure 6.13
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Close-up view of the boulder in the previous slide
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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
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Glaciers: a part of two basic cycles in the Earth system
Glacial deposits Depositional features Outwash plain, or valley train Kettles Drumlins Eskers Kames
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Glacial depositional features
Figure 6.18
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Kettle lakes Figure 6.18
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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
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Maximum extent of ice during the Ice Age
Figure 6.22
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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
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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
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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
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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
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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
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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
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A dry stream channel in the desert
Figure 6.28 A
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The same stream channel following heavy rainfall
Figure 6.28 B
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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
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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
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Landscape evolution in a mountainous desert – early
Figure 6.29 A
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Landscape evolution in a mountainous desert – middle
Figure 6.29 B
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Landscape evolution in a mountainous desert – late
Figure 6.29 C
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Deserts Wind erosion Deflation Abrasion Lifting of loose material
Produces Blowouts Desert pavement Abrasion
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Formation of desert pavement
Figure 6.34
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Deserts Types of wind deposits Loess Deposits of windblown silt
Extensive blanket deposits Primary sources are deserts and glacial stratified drift
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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
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Formation of sand dunes
Figure 6.37
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Deserts Types of wind deposits Sand dunes Types of sand dunes
Barchan dunes Transverse dunes Longitudinal dunes Parabolic dunes Star dunes
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Sand dune types Figure 6.38
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Sand dunes in the western United States
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