Coastal Landforms

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Coastal Landforms

• Erosional and depositional landforms

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Defining the Coastal Area / Zone

• The coastline is the line where the land and sea
  meet.
• The coast is a zone or strip of land extending
  from the coastline, which borders the sea to
  where the land rises inland. Its limit is marked
  by the level of high tide.
• The shore is the zone which lies between mean
  high low water mark and high water mark and
  constitutes both the backshore and foreshore.
• Backshore is the zone between mean high tide
  level and the coastline.
• Foreshore is the lower zone of the beach lying
  between the low and high water level.

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Defining the Coastal Area / Zone
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Features Produced by Wave or Marine Erosion

• Cliffs
• Headlands and bays
• Waves, arches and stacks
• Wave-cut platforms
• Blow Holes or Gloups and Goes

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Cliffs

• Most fundamental and ubiquitous feature of rock
  coastlines. Variations based on differences in
• Lithology
• Jointing
• Structure
• Degree of exposure
• Erosional History
• The dip of the rock
• Wave action
• Sub-aerial erosion

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Dead or a(Live)

• Classification into Live or Active cliffs, those
  which are experiencing wave erosion , or
  experiencing sub aerial activity, gullying, soil
  creep or slumping. They often have free-faces
• Dead cliffs are isolated from the sea by sand,
  shingle, sand-marsh deposits, and rock marsh

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Cliff Development

1. Removal of a wedge-shaped mass of rock, ( a
   notch) largely by the mechanical action of
   breaking waves, often utilizing some weakness
2. Once this has been initiated, basal attack,
   weathering and slumping, gullying and
   mass-movement wear down the headland
3. The cliff increases in height and the wave-cut
   platform is extended

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Cliff Development

• 4 As the wave cut platform develops, the process
  slows down as the shallower water over the
  platform slows down, and the basal attack is less
  intense.

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Headland and Bays

• Where there are alternating beds of hard and soft
  rocks, the hard rocks offer a greater resistant
  to erosion . They eventually stands out as
  headlands, that is, as promontories with steep
  cliff sides projecting out into sea.
• The softer rocks are easily eroded as they are
  less resistant to marine erosion. In due course
  an indentation or cure in the land, called a bay
  is formed. Bays are separated by headlands.

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Cliffs, Headland and Bays
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Processes

• Several other processes are found in and on
  cliffs, these include
• Sub-aerial processes ( Weathering and Mass
  movement) e.g. slumping, sliding, soil-creep,
  freeze-thaw, carbonation, salt-crystallization,
  biological weathering

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Rates of Cliff Recession

• Variation based on the
• Structure of the rock
• The Aspect
• The vegetation
• Mans impact
• Protect ional features

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Notches

• These are grooves that are eroded into cliffs
• Between mean high tide and low tide
• Extremely important in cliff development
• Develop in areas of weakness
• Variations include smooth rounded rocks in
  limestone and chalk ( chemical action)

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Wave Cut Platforms

• Tremendous variation
• Some are temporary, some permanent.
• Some are covered with sand and shingle, others
  have channels, trenches and hollows
• In hard rock the platforms are poorly developed
  whereas in soft homogenous rock there are broad,
  even surfaces with minor furrows

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Wave-cut platforms

• Formed by wave abrasion, and solution
• Delicate balance based on the resistance of the
  rock
• Weak rock will collapse
• Strong rock resistance will be minimal

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Rampanalgas- Mean Low tide
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Wave-cut platform at mean high tide
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Caves, arches and stacks

• Caves a natural underground hollow formed by
  erosion
• Arches formed by the wearing away of narrow
  headland, generally by the formation of two
  back-to back caves which eventually join. These
  are temporary and eventually collapse
• Stacks- Tall isolated pillars of rock that are
  free standing in the sea, alone or in a group.
  They may result from the collapse of an arch and
  are normally residual features formed from a
  former headland
• Stumps rocky platforms offshore that may be
  covered at high tide, but may be uncovered
  throughout the day.

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Arch
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Arch
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Stacks
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Stacks
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Geos

• Long, narrow gorge-like inlets, normally formed
  because of the collapse of a cave

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Features Produced by Marine Deposition

• Beaches
• Spits and Bars
• Tombolos
• Mudflats
• Sand Dunes

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Beaches

• A beach is an accumulation of materials such as
  boulders, pebbles, shingle, sand and mud on a
  sloping or shelving ground. The waves which
  break offshore result in its erosive power
  decreasing . This is caused by the swash and
  backwash which deposits materials on the shore.

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Beaches
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WHAT ARE SPITS?

• Spits are generally linear deposits of beach
  material attached at one end to land and free at
  the other. Where the direction of the coast
  changes, sediment carried by longshore drift may
  form a tongue of sand and other material, which
  is called a spit

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HOW ARE SPITS FORMED?
Spits are formed when a large accumulation of
material forms a narrow strip of land that juts
out into the sea but is still connected to the
mainland.Where a river carries large amounts of
material into a bay, waves moving obliquely will
transport the material in a diagonal direction
along the beach by the process of longshore
drift. An example of a spit is the Cocal spit at
the mouth of the Nariva River on the east coast
of Trinidad

• .

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CONDITIONS NECESSARY TO FORM A SPIT

• There must be a good supply of sand and other
  sediments
• Waves must approach the coast at an angle, so
  that longshore drift moves material along the
  coast
• The sea must be relatively shallow
• The sea is usually fairly calm, with low-energy
  constructive waves

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WHAT ARE TOMBOLOS?

• A linear deposit of sand or stones, formed by
  longshore drift, which joins an island to the
  mainland is called a tombolo.
• An example of a tombolo is the Palisadoes in
  Jamaica

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TOMBOLOS
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MUDFLATS

• Mudflats are lowlying parts of the coast which
  are submerged at high tide and low tide. They are
  normally located behind a bar or sandpit or
  besides estuaries and are comprised of silt or
  clay. In tropical areas mudflats support dense
  tropical mangrove vegetation community often with
  large area of swamp.

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MUDFLATS
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SAND DUNES

• Some sea shores consist of ridges of sand
  deposits by waves and shaped by wind. These are
  termed sand dunes. They are confined to coastal
  areas which are lowlying and are above sea high
  water tidal level.
• The onshore winds blowing across sandy beaches
  constantly renew and shape the sand deposits.
  Vegetation on the coast trap the sand and causes
  it to be stationary .
• Sand dunes are common in Port Royal in Jamaica
  and Sandy Belt in Guyana.

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Sand Dunes
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THE END Prepared by Ms . Fouchong