Erosion

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3

To grow, corals need:

Clear, warm, shallow water

Wave action

Corbis Digital Stock

Slide 24

Coral reefs

Fringing reef - directly attached to an island or coast

Barrier reef - lagoon between coast and reef

Atoll reef - circular reef surrounding a lagoon (no land in centre)

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Aeolian (Eolian) landscapes

Wind erosion, transport and deposition

Occurs in dry regions, with little vegetation such as deserts and coastal landscapes

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Wind Erosion

Faster the air flows, more erosion

Erodes more rapidly if wind blows constantly from one direction

2 TYPES OF WIND EROSION

ABRASION and DEFLATION

Slide 27

Deflation hollows

Removal of fine particles by wind leaves hollows behind (DEFLATION HOLLOWS)

Also leaves a surface of closely packed stones (DESERT PAVEMENT)

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Wind transportation

- Very fine material may be carried in suspension in the air

- But larger particles may be moved by 2 methods:

SURFACE CREEP &

SALTATION

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1.) SURFACE CREEP

- material is rolled along the surface

- accounts for 20% of wind transport

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2.) SALTATION

- The asymmetrical bouncing of sand grains

- Accounts for 80% of wind transport

- Cause of shifting sand dunes

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Aggradational land forms

SAND SEAS (ERGS)

= only 25% of the world's deserts

surface may be covered in RIPPLES

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Sand dunes

are ridges of wind deposited sand

- Usually 3 to 15 metres high, but can reach 180 metres

- A continuously changing dune is ACTIVE

Corbis Digital Stock

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The formation of dunes depends on:

- amount of sand

- speed and direction of wind - occurrence of vegetation

Corbis Digital Stock

Slide 34

wind direction

BACKSLOPE

SLIPFACE

movement of sand

angle of repose

crest

Slide 35

Types of sand dune