earth science, 12e glaciers, deserts, and wind chapter 6
TRANSCRIPT
Earth Science, Earth Science, 12e12e
Glaciers, Deserts, Glaciers, Deserts, and Windand WindChapter 6Chapter 6
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system 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
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system 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
Currently ice sheets cover Currently ice sheets cover Greenland and AntarcticaGreenland and Antarctica
Figure 6.2
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system 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
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system 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
The glacial budgetThe glacial budget
Figure 6.7
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system cycles in the Earth system
Glaciers erode by • Plucking – lifting of rock blocks • Abrasion
• Rock flour (pulverized rock) • Striations (grooves in the bedrock)
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system cycles in the Earth system
Landforms created by glacial erosion • Glacial trough • Hanging valley • Cirque • Arête• Horn• Fiord
Erosional landforms created Erosional landforms created
by alpine glaciersby alpine glaciers
Figure 6.10 C
The Matterhorn in The Matterhorn in the Swiss Alpsthe Swiss Alps
Figure 6.12
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system 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
Glacial till is typically Glacial till is typically unstratified and unsortedunstratified and unsorted
Figure 6.13
Close-up view of the boulder Close-up view of the boulder in the previous slidein the previous slide
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system cycles in the Earth system
Glacial deposits • Depositional features
• Moraines – layers or ridges of till• Types of moraines
• Lateral• Medial• End• Ground
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system cycles in the Earth system
Glacial deposits • Depositional features
• Outwash plain, or valley train • Kettles• Drumlins• Eskers• Kames
Glacial depositional Glacial depositional featuresfeatures
Figure 6.18
Kettle lakesKettle lakes
Figure 6.18
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system 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
Maximum extent of ice Maximum extent of ice during the Ice Ageduring the Ice Age
Figure 6.22
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system 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
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system 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
Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system 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
Deserts 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
Deserts 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
Deserts 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
A dry stream channel A dry stream channel in the desertin the desert
Figure 6.28 A
The same stream channel The same stream channel following heavy rainfallfollowing heavy rainfall
Figure 6.28 B
Deserts 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
Deserts 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
Landscape evolution in a Landscape evolution in a mountainous desert – early mountainous desert – early
Figure 6.29 A
Landscape evolution in a Landscape evolution in a mountainous desert – middle mountainous desert – middle
Figure 6.29 B
Landscape evolution in a Landscape evolution in a mountainous desert – latemountainous desert – late
Figure 6.29 C
Deserts Deserts
Wind erosion • Deflation
• Lifting of loose material • Produces
• Blowouts• Desert pavement
• Abrasion
Formation of Formation of desert pavementdesert pavement
Figure 6.34
Deserts Deserts
Types of wind deposits • Loess
• Deposits of windblown silt • Extensive blanket deposits • Primary sources are deserts and glacial stratified
drift
Deserts 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
Formation of sand dunesFormation of sand dunes
Figure 6.37
Deserts Deserts
Types of wind deposits • Sand dunes
• Types of sand dunes • Barchan dunes• Transverse dunes• Longitudinal dunes • Parabolic dunes• Star dunes
Sand dune typesSand dune types
Figure 6.38
Sand dunes in the Sand dunes in the western United Stateswestern United States