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The Work of Waves and Wind

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Delta and Volcano Coasts. DELTA - deposit by rivers entering the sea ... Volcano coasts develop in volcanic deposits. Low cliffs form in fresh lava. Coral reefs ... – PowerPoint PPT presentation

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Title: The Work of Waves and Wind


1
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

2
COASTAL LANDFORMS
wave length
crest
trough
wave height
particles in waves follow a circular pattern
3
At the shoreline
  • Water becomes shallow, wave height increases
    because wave length decreases
  • Waves become steeper, then collapse (breakers)

4
  • Surf - sequence of breaking waves
  • Swash - water sliding up beach
  • Backwash - water flowing back down beach to sea

5
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

6
Wave refraction
Bay
7
  • Waves arriving at bays are slow (deposition)
  • At headlands, faster (erosion)

8
  • A sequence of features is produced as headlands
    are degraded
  • Sea cliffs
  • Waves erode base -undercutting

the cliff retreats
9
  • Also produces sea caves
  • As cliffs retreat produces a wave-cut platform

10
  • Headlands may be eroded back leaving a remnant
    (stack)

stack
11
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
12
Coastal deposition
  • Result of longshore drift and a lot of sediment
  • produces extensions of deposit from the
    shoreline

13
spit curved extension
  • May grow across a bay (baymouth bar)
  • May link an island to the main land (tombolo)

14
  • 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
15
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
16
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
17
Types of Coastline
Submergence and emergence changes coastlines
Pocket beaches
18
Emergent coast
  • Uplifted land surface
  • Coastal landforms are found above present sea
    level

a wave-cut platform when elevated - uplifted
marine terrace
19
Submergent coast
  • Rise in sea level
  • Submergent coast
  • Landforms under water
  • A ria coastline is an example of submergence

20
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

21
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

22
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

23
Coral reefs
  • Corals build up calcium deposits to produce reefs
  • To grow, corals need
  • Clear, warm, shallow water
  • Wave action

Corbis Digital Stock
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)

25
AEOLIAN (Eolian) LANDSCAPES
  • Wind erosion, transport and deposition
  • Occurs in dry regions, with little vegetation
    such as deserts and coastal landscapes

26
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


27
DEFLATION HOLLOWS Removal of fine particles by
wind leaves hollows behind (DEFLATION
HOLLOWS) Also leaves a surface of closely packed
stones (DESERT PAVEMENT)
28
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
29
1.) SURFACE CREEP - material is rolled along the
surface - accounts for 20 of wind transport
30
2.) SALTATION - The asymmetrical bouncing of
sand grains - Accounts for 80 of wind
transport - Cause of shifting sand dunes
31
Aggradational land forms SAND SEAS (ERGS)
only 25 of the world's deserts surface may be
covered in RIPPLES
32
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
33
The formation of dunes depends on - amount of
sand - speed and direction of wind -
occurrence of vegetation
Corbis Digital Stock
34
wind direction
BACKSLOPE
SLIPFACE
crest
angle of repose
movement of sand
35
TYPES OF SAND DUNE 1.) BARCHAN - most common
type - crescent-shaped
backslope
slip face
Wind direction
36
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
37
  • 3.) TRANSVERSE DUNES
  • low sand ridge at right angles to the wind
    direction
  • may form because of large amounts of sand

wind
38
  • 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
39
LOESS
  • Finely textured sediment wind-blown long
    distances
  • Wind-blown glacial debris formed large deposits
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