Learning Objectives:
Glaciers A thick mass of ice
that forms over land from the compaction and recrystallization of snow and shows evidence
of past or present flow
Types of Glaciers
Valley or alpine glaciers
Ice sheets or continental
Ice caps
Piedmont glaciers
Types of Glaciers
Valley, or alpine glaciers - form in mountainous areas
Ice sheets, or continental
Large scale
e.g., Over Greenland
Other types
Ice caps
Piedmont glaciers
Movement of glacial ice
Types of glacial movements
Flow
Slipping along the ground
Zone of fracture
Uppermost 50 meters
Crevasses from in brittle ice
Zone of accumulation - the area where a glacier forms
Zone of wastage - the area where there is a net loss due to melting
Glaciers erode by
Plucking - lifting of rock blocks
Abrasion
Rock flour (pulverized rock)
Striations (grooves in the bedrock)
Erosional features of valley glaciers
Glacial trough
Hanging valley
Cirque
Arete
Horn
Fiord
Glacial deposits
Glacial drift
All sediments of glacial origin
Types of glacial drift
Till
Material that is deposited directly by the ice
Glacial erratics (boulders embedded in till)
Striated drift
Deposited by meltwater
Sediment is sorted
Depositional features
Moraines
Layers or ridges of till
Types
Lateral
Medial
End
Ground
Outwash plain, or valley train
Kettles
Drumlins
Eskers
Kames
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
Indirect effects of Ice Age glaciers
Migration of animals and plants
Rebounding upward of the crust
Worldwide change in sea level
Climate changes
Causes of glaciation
Successful theory must account for
Cooling of Earth, as well as
Short-term climatic change
Proposed possible causes
Plate tectonics
Continents were arranged differently
Changes in oceanic circulation
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
Geological 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
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
Wash
Arroyo
Wadi, donga, or nullah
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
Evolution of a desert landscape
Uplifted crustal blocks
Interior drainage into basins produces
Alluvial fans and bajadas
Playas and playa lakes
Winds erosion
By deflation
Lifting of loose material
Produces
Blowouts
Desert pavement
By abrasion
Types of wind deposits
Loess
Deposits of windblown silt
Extensive blanket deposits
Primary sources are
Deserts
Glacial stratified drift
Sand dunes
Mounds and ridges of sand formed from the wind’s bed load
Characteristics features
Slip face-the leeward slope of the dune
Cross beds-sloping layers of sand in the dune
Types of sand dunes
Barchan dunes
Transverse dunes
Longitudinal dunes
Parabolic dunes
Star dunes
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