Coastal Landforms

Document Sample
Coastal Landforms Powered By Docstoc
					Coastal Landforms

Erosional and depositional
    Defining the Coastal Area / Zone
• The coastline is the line where the land and sea
•   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.
Defining the Coastal Area / Zone
Features Produced by Wave or
Marine Erosion

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

• 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
Rates of Cliff Recession

• Variation based on the
• Structure of the rock
• The Aspect
• The vegetation
• Man’s impact
• Protect ional features
•   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)
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
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
Rampanalgas- Mean Low tide
Wave-cut platform at mean high
Caves, arches and stacks
• Caves – a natural underground hollow formed by
• 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.

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

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

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

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

• 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.
• 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.
Sand Dunes
       THE END
Prepared by: Ms . Fouchong

Shared By: