erosion
TRANSCRIPT
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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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wave length
wave height
crest
trough
particles in waves follow a circular pattern
COASTAL LANDFORMS
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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
Headland
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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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• May grow across a bay (baymouth bar)
• May link an island to the main land (tombolo)
spit = curved extension
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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 Earth’s 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 formsSAND SEAS (ERGS)
= only 25% of the world's desertssurface may be covered in RIPPLES
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SAND DUNESare 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
movement of sandangle of repose
crest
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TYPES OF SAND DUNE1.) BARCHAN- most common type- crescent-shaped
Wind direction
backslope
slip face
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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
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