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Chapter 5 Glaciers, Deserts, and Wind

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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