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The Work of Waves and Wind. Objectives: Explain the characteristics of ocean waves and tides Present coastline features of erosion, transport and deposition Examine the processes of wind erosion and deposition Differentiate different types of dune Describe the wind deposit LOESS.

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the work of waves and wind
The Work of Waves and Wind
  • Objectives:
  • Explain the characteristics of ocean waves and tides
  • Present coastline features of erosion, transport and deposition
  • Examine the processes of wind erosion and deposition
  • Differentiate different types of dune
  • Describe the wind deposit LOESS
slide2

COASTAL LANDFORMS

wave length

crest

trough

wave height

particles in waves follow a circular pattern

at the shoreline
At the shoreline
  • Water becomes shallow, wave height increases because wave length decreases
  • Waves become steeper, then collapse (breakers)
slide4
Surf - sequence of breaking waves
  • Swash - water sliding up beach
  • Backwash - water flowing back down beach to sea
wave refraction
Wave refraction
  • Close to coast, water gets more shallow
  • Waves are slowed down
  • If waves arrive at an angle, one part is slower than the rest
  • Causes waves to bend = wave refraction
slide7
Waves arriving at bays are slow (deposition)
  • At headlands, faster (erosion)
slide8
A sequence of features is produced as headlands are degraded
  • Sea cliffs
  • Waves erode base -undercutting

the cliff retreats

slide9

Also produces sea caves

  • As cliffs retreat produces a wave-cut platform
longshore drift
Longshore drift
  • Waves arrive at a coast at an angle (swash)
  • Backwash returns at 90degrees

Sand is moved along the beach = longshore drift or longshore current

coastal deposition
Coastal deposition
  • Result of longshore drift and a lot of sediment
  • = produces extensions of deposit from the shoreline
slide13

spit = curved extension

  • May grow across a bay (baymouth bar)
  • May link an island to the main land (tombolo)
slide14

TIDES

  • Daily changes in sea levels
  • Tides rise (FLOOD) to produce a HIGH TIDE
  • And fall (EBB) (LOW TIDE)
  • Produced by the gravitational pull that the Sun and Moon exert on the Earth’s surface (including the oceans)

Moon/

Sun

slide15

This side is pulled towards the Sun and/or Moon by gravitational attraction

This side bulges out because of inertia

Therefore, there are two high tides on Earth at any one time

slide16

Every 24 hours 50 minutes any point on the Earth rotates through two bulges

Each location experiences 2 high (FLOOD) tides and 2 low (EBB) tides

types of coastline
Types of Coastline

Submergence and emergence changes coastlines

Pocket beaches

emergent coast
Emergent coast
  • Uplifted land surface
  • Coastal landforms are found above present sea level

a wave-cut platform when elevated - uplifted marineterrace

submergent coast
Submergent coast
  • Rise in sea level
  • Submergent coast
  • Landforms under water
  • A ria coastline is an example of submergence
submergence shorlines
Submergence Shorlines
  • Ria coast - shorline valleys eroded by rivers are submerged
    • has many offshore islands
    • exposure to waves erodes islands and headlands
  • Fiord coast - shoreline valleys created by glaciers are submerged
    • valleys are deep and straight
    • because of the depth, there are few beaches
barrier island coasts
Barrier Island Coasts
  • Occur on low lying coasts with gentle gradients
  • BARRIER ISLANDS - low ridges of sand built by waves
    • behind the islands are lagoons
    • shallow water with tidal deposits
  • TIDAL INLETS - gaps between the islands
delta and volcano coasts
Delta and Volcano Coasts
  • DELTA - deposit by rivers entering the sea
  • Water slows down and spreads out as it enters
  • Channel divides and subdivides to create DISTRIBUTARIES
  • Volcano coasts develop in volcanic deposits
  • Low cliffs form in fresh lava
coral reefs
Coral reefs
  • Corals build up calcium deposits to produce reefs
  • To grow, corals need:
    • Clear, warm, shallow water
    • Wave action

Corbis Digital Stock

coral reefs24
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)
aeolian eolian landscapes

AEOLIAN (Eolian) LANDSCAPES

Wind erosion, transport and deposition

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

wind erosion
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
slide27

DEFLATION HOLLOWS

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

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

slide28

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

slide29

1.) SURFACE CREEP

- material is rolled along the surface

- accounts for 20% of wind transport

slide30

2.) SALTATION

- The asymmetrical bouncing of sand grains

- Accounts for 80% of wind transport

- Cause of shifting sand dunes

slide31

Aggradational land forms

SAND SEAS (ERGS)

= only 25% of the world's deserts

surface may be covered in RIPPLES

slide32

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

slide33

The formation of dunes depends on:

- amount of sand

- speed and direction of wind - occurrence of vegetation

Corbis Digital Stock

slide34

wind direction

BACKSLOPE

SLIPFACE

crest

angle of repose

movement of sand

slide35

TYPES OF SAND DUNE

1.) BARCHAN

- most common type

- crescent-shaped

backslope

slip face

Wind direction

slide36

2.) PARABOLIC DUNES

- crescent-shaped but with the concave side on the windward side

- usually elongated

- may develop in associated with deflation hollows

Wind direction

slide37

3.) TRANSVERSE DUNES

  • low sand ridge at right angles to the wind direction
  • may form because of large amounts of sand

wind

slide38

4.) LONGITUDINAL DUNES

  • low sand ridges parallel to the wind direction
  • may form because of a limited amount of sand
  • also known as seif dunes

wind

loess
LOESS
  • Finely textured sediment wind-blown long distances
  • Wind-blown glacial debris formed large deposits
slide40

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