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Chapter 6 Lecture
Earth Science
Fourteenth Edition
Glaciers, Deserts,
and Wind
Jennifer Mangan
James Madison University
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Glaciers
• 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
• Types of glaciers
– Valley, or alpine glaciers – form in mountainous areas
– Kennicott Glacier
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Glaciers
• Types of glaciers
– Ice sheets or
continental glaciers
• Large scale
• e.g., Over Greenland
and Antarctica
– Other types
• Ice caps and
piedmont glaciers
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Glacier Movement
• 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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Crevasses
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Glacier Movement
• 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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Glacial Erosion
• Glaciers erode by
– Plucking – lifting of rock blocks
– Abrasion
• Rock flour (pulverized rock)
• Striations (grooves in the bedrock)
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Glacial Erosion
• Landforms created by glacial erosion
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Glacial trough
Hanging valley
Cirque
Arête
Horn
Fiord
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Erosional Landforms Created by Alpine
Glaciers
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The Matterhorn in the Swiss Alps
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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 Deposits
• Depositional features
– Moraines – layers or ridges of till
– Types of moraines
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Lateral
Medial
End
Ground
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End Moraines of the Great Lakes Region
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Glacial Deposits
• Depositional features
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Outwash plain or valley train
Kettles
Drumlins
Eskers
Kames
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Glacial Depositional Features
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Ice Age Glaciers
• 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 percent of Earth’s land area
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Extent of Ice Age Glaciation
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Ice Age Glaciers
• Effects of Ice Age glaciers
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Migration of animals and plants
Rebounding upward of the crust
Worldwide change in sea level
Climatic changes
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Ice Age Sea Level
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Causes of Ice Ages
• 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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Late Paleozoic Ice Age
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Causes of Ice Ages
• 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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Orbital Variations
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Deserts
• Any situation with a water deficiency
• Distribution and causes of dry lands
– Global distribution of air pressure and winds
– Deep interiors of landmasses
– Presence of high mountains
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Global Dry Climate Distribution
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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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Desert Stream Channel
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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 Basin and
Range Region
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Deserts
• Wind erosion
– Deflation
• Lifting of loose material
• Produces
– Blowouts
– Desert pavement
– Abrasion
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Formation of Desert Pavement
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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
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Deserts
• Types of wind deposits
– Sand dunes
• Types of sand dunes
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Barchan dunes
Transverse dunes
Longitudinal dunes
Parabolic dunes
Star dunes
Sand Dune Types
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