Earth Science 13 e Tarbuck Lutgens 2012 Pearson
Earth Science, 13 e Tarbuck & Lutgens © 2012 Pearson Education, Inc.
Glaciers, Deserts, and Wind Earth Science, 13 e Chapter 6 Stanley C. Hatfield Southwestern Illinois College © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. Glaciers are a part of both the hydrologic cycle and rock cycle v. 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 © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. Types of glaciers • Valley, or alpine glaciers – form in mountainous areas • Ice sheets, or continental glaciers • Large scale • e. g. , Over Greenland Antarctica • Other types • Ice caps and piedmont glaciers © 2012 Pearson Education, Inc.
Currently ice sheets cover Greenland Antarctica © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. 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 © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. 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 © 2012 Pearson Education, Inc.
The glacial budget © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. Glaciers erode by • Plucking – lifting of rock blocks • Abrasion • Rock flour (pulverized rock) • Striations (grooves in the bedrock) © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. Landforms created by glacial erosion • • • Glacial trough Hanging valley Cirque Arête Horn Fiord © 2012 Pearson Education, Inc.
Erosional landforms created by alpine glaciers © 2012 Pearson Education, Inc.
The Matterhorn in the Swiss Alps © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. 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 © 2012 Pearson Education, Inc.
Glacial till is typically unstratified and unsorted © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. Glacial deposits • Depositional features • Moraines – layers or ridges of till • Types of moraines • • Lateral Medial End Ground © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. Glacial deposits • Depositional features • • • Outwash plain, or valley train Kettles Drumlins Eskers Kames © 2012 Pearson Education, Inc.
Glacial depositional features © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. 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 © 2012 Pearson Education, Inc.
Maximum extent of ice during the Ice Age © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. 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 © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. 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 © 2012 Pearson Education, Inc.
Glaciers: a part of two basic cycles in the Earth system v. 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 © 2012 Pearson Education, Inc.
Deserts v. 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 © 2012 Pearson Education, Inc.
Deserts v. 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 © 2012 Pearson Education, Inc.
Deserts v. 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 © 2012 Pearson Education, Inc.
A dry stream channel in the desert © 2012 Pearson Education, Inc.
The same stream channel following heavy rainfall © 2012 Pearson Education, Inc.
Deserts v. 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 © 2012 Pearson Education, Inc.
Deserts v. 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 © 2012 Pearson Education, Inc.
Landscape evolution in a mountainous desert – early © 2012 Pearson Education, Inc.
Landscape evolution in a mountainous desert – middle © 2012 Pearson Education, Inc.
Landscape evolution in a mountainous desert – late © 2012 Pearson Education, Inc.
Deserts v. Wind erosion • Deflation • Lifting of loose material • Produces • Blowouts • Desert pavement • Abrasion © 2012 Pearson Education, Inc.
Formation of desert pavement © 2012 Pearson Education, Inc.
Deserts v. Types of wind deposits • Loess • Deposits of windblown silt • Extensive blanket deposits • Primary sources are deserts and glacial stratified drift © 2012 Pearson Education, Inc.
Deserts v. 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 © 2012 Pearson Education, Inc.
Formation of sand dunes © 2012 Pearson Education, Inc.
Deserts v. Types of wind deposits • Sand dunes • Types of sand dunes • • • Barchan dunes Transverse dunes Longitudinal dunes Parabolic dunes Star dunes © 2012 Pearson Education, Inc.
Sand dune types © 2012 Pearson Education, Inc.
End of Chapter 6 © 2012 Pearson Education, Inc.
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