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Lecture Outlines

PowerPoint

Chapter 6

Earth Science 11e

Tarbuck/Lutgens

Earth Science, 11e

Glaciers, Deserts,

and Wind

Chapter 6

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 recrystal-

lization 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

Figure 6.1

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

Glaciers move by 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

Figure 6.6

Glaciers: a part of two basic

cycles in the Earth system

Glaciers erode by

• 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

Erosional landforms created

by alpine glaciers

Figure 6.9 C

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

Figure 6.13

Close-up view of the boulder

in the previous slide

Glaciers: a part of two basic

cycles in the Earth system

Glacial deposits

• 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

Figure 6.18

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

Figure 6.19

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

Figure 6.26 A

The same stream channel

following heavy rainfall

Figure 6.26 B

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

Figure 6.27 A

Landscape evolution in a

mountainous desert – middle stage

Figure 6.27 B

Landscape evolution in a

mountainous desert – late stage

Figure 6.27 C

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

Figure 6.32

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

Figure 6.35

Deserts

Types of wind deposits

• Sand dunes

• Types of sand dunes

• Barchan dunes

• Transverse dunes

• Longitudinal dunes

• Parabolic dunes

• Star dunes

Sand dune types

Figure 6.36

Sand dunes in the

western United States

End of Chapter 6