EARTH SCIENCE, 10E
EDWARD J. TARBUCK &
FREDERICK K. LUTGENS
GLACIERS, DESERTS,
AND WIND
CHAPTER 5
EARTH SCIENCE, 10E
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
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
CURRENTLY
CONTINENTAL ICE
SHEETS COVER
GREENLAND AND
ANTARCTICA
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
BASAL SLIDING AND INTERNAL PLASTIC FLOW
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
THE GLACIAL BUDGET
GLACIERS: A PART OF TWO BASIC CYCLES IN THE EARTH SYSTEM
Glaciers erosion
•Plucking – lifting of rock blocks
•Abrasion
Rock flour (pulverized rock)
Striations (grooves in the bedrock)
GLACIERS: A PART OF TWO BASIC CYCLES IN THE EARTH SYSTEM
Landforms created by glacial erosion
•Glacial trough
•Hanging valley
•Cirque
•Arête
•Horn
•Fiord
•Tarn
LANDFORMS CREATED BY ALPINE GLACIERS
THE MATTERHORN IN THE SWISS ALPS
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
GLACIAL TILL IS TYPICALLY UNSTRATIFIED AND UNSORTED
CLOSE-UP VIEW OF THE BOULDER IN THE PREVIOUS SLIDE
GLACIERS: A PART OF TWO BASIC CYCLES IN THE EARTH SYSTEM
Glacial Deposition
•Depositional features
Moraines – layers or ridges of till
Types of moraines
•Lateral
•Medial
•End
•Ground
GLACIERS: A PART OF TWO BASIC CYCLES IN THE EARTH SYSTEM
Glacial deposits
•Depositional features
Outwash plain, or valley train
Kettles
Drumlins
Eskers
Kames
GLACIAL DEPOSITIONAL FEATURES
A DRUMLIN IN UPSTATE NEW YORK
KETTLE LAKES
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
MAXIMUM EXTENT OF ICE DURING THE ICE AGE
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
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
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
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
 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
 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
IN THE DESERT
THE SAME STREAM CHANNEL FOLLOWING HEAVY
RAINFALL
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
 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 MOUNTAINOUS
DESERT – EARLY STAGE
LANDSCAPE EVOLUTION IN A MOUNTAINOUS
DESERT – MIDDLE STAGE
LANDSCAPE EVOLUTION IN A MOUNTAINOUS
DESERT – LATE STAGE
INSELBERGS IN
SOUTHERN CALIFORNIA
DESERTS
 Wind erosion
• Deflation
 Lifting of loose material
 Produces
•Blowouts
•Desert pavement
• Abrasion
FORMATION OF A DESERT BLOWOUT
FORMATION OF DESERT PAVEMENT
DESERTS
 Types of wind deposits
• Loess
 Deposits of windblown silt
 Extensive blanket deposits
 Primary sources are deserts and glacial stratified drift
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 DUNES
DESERTS
 Types of wind deposits
• Sand dunes
 Types of sand dunes
•Barchan dunes
•Transverse dunes
•Longitudinal dunes
•Parabolic dunes
•Star dunes
SAND DUNE TYPES
SAND DUNES IN THE
WESTERN UNITED STATES