The Work of Waves and Wind

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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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COASTAL LANDFORMS
wave length
crest
trough
wave height
particles in waves follow a circular pattern
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At the shoreline

• Water becomes shallow, wave height increases
  because wave length decreases
• Waves become steeper, then collapse (breakers)

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• Surf - sequence of breaking waves
• Swash - water sliding up beach
• Backwash - water flowing back down beach to sea

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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

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Wave refraction
Bay
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• Waves arriving at bays are slow (deposition)
• At headlands, faster (erosion)

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• A sequence of features is produced as headlands
  are degraded
• Sea cliffs
• Waves erode base -undercutting

the cliff retreats
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• Also produces sea caves
• As cliffs retreat produces a wave-cut platform

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• Headlands may be eroded back leaving a remnant
  (stack)

stack
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Longshore drift

• Waves arrive at a coast at an angle (swash)
• Backwash returns at 90 degrees

Sand is moved along the beach longshore drift
or longshore current
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Coastal deposition

• Result of longshore drift and a lot of sediment
• produces extensions of deposit from the
  shoreline

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spit curved extension

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

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• 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 Earths surface (including
  the oceans)

Moon/ Sun
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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
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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
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Types of Coastline
Submergence and emergence changes coastlines
Pocket beaches
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Emergent coast

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

a wave-cut platform when elevated - uplifted
marine terrace
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Submergent coast

• Rise in sea level
• Submergent coast
• Landforms under water
• A ria coastline is an example of submergence

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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

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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

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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

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Coral reefs

• Corals build up calcium deposits to produce reefs
• To grow, corals need
• Clear, warm, shallow water
• Wave action

Corbis Digital Stock
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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

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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
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wind direction
BACKSLOPE
SLIPFACE
crest
angle of repose
movement of sand
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TYPES OF SAND DUNE 1.) BARCHAN - most common
type - crescent-shaped
backslope
slip face
Wind direction
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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
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• 3.) TRANSVERSE DUNES
• low sand ridge at right angles to the wind
  direction
• may form because of large amounts of sand

wind
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• 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
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LOESS

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