Earth Science, 12e Glaciers, Deserts, and Wind Chapter 6.

Earth Science, Earth Science, 12e12e

Glaciers, Deserts, Glaciers, Deserts, and Windand WindChapter 6Chapter 6

Glaciers: a part of two basic Glaciers: a part of two basic cycles in the Earth system 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


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 ice sheets cover Currently ice sheets cover Greenland and AntarcticaGreenland and Antarctica

Figure 6.2


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


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 budgetThe glacial budget

Figure 6.7


Glaciers erode by • Plucking – lifting of rock blocks • Abrasion

• Rock flour (pulverized rock) • Striations (grooves in the bedrock)


Landforms created by glacial erosion • Glacial trough • Hanging valley • Cirque • Arête• Horn• Fiord

Erosional landforms created Erosional landforms created

by alpine glaciersby alpine glaciers

Figure 6.10 C

The Matterhorn in The Matterhorn in the Swiss Alpsthe Swiss Alps

Figure 6.12


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 Glacial till is typically unstratified and unsortedunstratified and unsorted

Figure 6.13

Close-up view of the boulder Close-up view of the boulder in the previous slidein the previous slide


Glacial deposits • Depositional features

• Moraines – layers or ridges of till• Types of moraines

• Lateral• Medial• End• Ground


Glacial deposits • Depositional features

• Outwash plain, or valley train • Kettles• Drumlins• Eskers• Kames

Glacial depositional Glacial depositional featuresfeatures

Figure 6.18

Kettle lakesKettle lakes

Figure 6.18


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 Maximum extent of ice during the Ice Ageduring the Ice Age

Figure 6.22


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


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


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 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 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 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 A dry stream channel in the desertin the desert

Figure 6.28 A

The same stream channel The same stream channel following heavy rainfallfollowing heavy rainfall

Figure 6.28 B

Deserts 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 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 Landscape evolution in a mountainous desert – early mountainous desert – early

Figure 6.29 A

Landscape evolution in a Landscape evolution in a mountainous desert – middle mountainous desert – middle

Figure 6.29 B

Landscape evolution in a Landscape evolution in a mountainous desert – latemountainous desert – late

Figure 6.29 C

Deserts Deserts

Wind erosion • Deflation

• Lifting of loose material • Produces

• Blowouts• Desert pavement

• Abrasion

Formation of Formation of desert pavementdesert pavement

Figure 6.34

Deserts Deserts

Types of wind deposits • Loess

• Deposits of windblown silt • Extensive blanket deposits • Primary sources are deserts and glacial stratified

drift

Deserts 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 dunesFormation of sand dunes

Figure 6.37

Deserts Deserts

Types of wind deposits • Sand dunes

• Types of sand dunes • Barchan dunes• Transverse dunes• Longitudinal dunes • Parabolic dunes• Star dunes

Sand dune typesSand dune types

Figure 6.38

Sand dunes in the Sand dunes in the western United Stateswestern United States

Earth Science, 12e Glaciers, Deserts, and Wind Chapter 6.

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