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Chapter 6 Lecture Earth Science Fourteenth Edition Glaciers, Deserts, and Wind Jennifer Mangan James Madison University © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. Glaciers • Types of glaciers – Valley, or alpine glaciers – form in mountainous areas – Kennicott Glacier © 2015 Pearson Education, Inc. Glaciers • Types of glaciers – Ice sheets or continental glaciers • Large scale • e.g., Over Greenland and Antarctica – Other types • Ice caps and piedmont glaciers © 2015 Pearson Education, Inc. Glacier Movement • Types of glacial movements – Plastic flow – Slipping along the ground • Zone of fracture – Uppermost 50 meters – Crevasses form in brittle ice © 2015 Pearson Education, Inc. Crevasses © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. Glacial Erosion • Glaciers erode by – Plucking – lifting of rock blocks – Abrasion • Rock flour (pulverized rock) • Striations (grooves in the bedrock) © 2015 Pearson Education, Inc. Glacial Erosion • Landforms created by glacial erosion – – – – – – Glacial trough Hanging valley Cirque Arête Horn Fiord © 2015 Pearson Education, Inc. Erosional Landforms Created by Alpine Glaciers © 2015 Pearson Education, Inc. The Matterhorn in the Swiss Alps © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. Glacial Deposits • Depositional features – Moraines – layers or ridges of till – Types of moraines • • • • Lateral Medial End Ground © 2015 Pearson Education, Inc. End Moraines of the Great Lakes Region © 2015 Pearson Education, Inc. Glacial Deposits • Depositional features – – – – – Outwash plain or valley train Kettles Drumlins Eskers Kames © 2015 Pearson Education, Inc. Glacial Depositional Features © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. Extent of Ice Age Glaciation © 2015 Pearson Education, Inc. Ice Age Glaciers • Effects of Ice Age glaciers – – – – Migration of animals and plants Rebounding upward of the crust Worldwide change in sea level Climatic changes © 2015 Pearson Education, Inc. Ice Age Sea Level © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. Late Paleozoic Ice Age © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. Orbital Variations © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. Global Dry Climate Distribution © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. Desert Stream Channel © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. Landscape Evolution in a Basin and Range Region © 2015 Pearson Education, Inc. Deserts • Wind erosion – Deflation • Lifting of loose material • Produces – Blowouts – Desert pavement – Abrasion © 2015 Pearson Education, Inc. Formation of Desert Pavement © 2015 Pearson Education, Inc. Deserts • Types of wind deposits – Loess • Deposits of windblown silt • Extensive blanket deposits • Primary sources are deserts and glacial stratified drift © 2015 Pearson Education, Inc. 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 © 2015 Pearson Education, Inc. Formation of Sand Dunes © 2015 Pearson Education, Inc. Deserts • Types of wind deposits – Sand dunes • Types of sand dunes – – – – – © 2015 Pearson Education, Inc. Barchan dunes Transverse dunes Longitudinal dunes Parabolic dunes Star dunes Sand Dune Types © 2015 Pearson Education, Inc.