1 . Headlands and Bays form along coastlines where rocks outcrop at 90 o to the coast 2 . Here there are alternate bands of resistant and less resistant rock 3. Where there is soft rock (e.g. clay), erosion is rapid - and bays are formed (indent in coastline) 4. Where there is more resistant rock (e.g. chalk), erosion is much slower - headlands are formed as the harder rock is left sticking out into the sea 5. Exposed headlands then become vulnerable to destructive waves but help to shelter neighbouring bays.
1 . Wave erosion is greatest where waves break at the base of a cliff . 2 . A wave-cut notch is formed at the base of a cliff due to undercutting by wave erosion ( e . g . abrasion / hydraulic action ) 3 . As undercutting continues, the cliff will eventually collapse and retreat . 4 . The gentle sloping rocky platform left behind when the cliff retreats is called a wave-cut platform . This feature is only exposed at low - tide .
The sea attacks the foot of the cliff ( through processes of erosion such as abrasion and hydraulic action ) , eroding areas of weakness ( e . g . joints - cracks in the rock ) 2 . These cracks get larger developing into small caves 3. Further erosion widens and deepens the cave until it is eroded through the headland forming an arch (this process may occur quicker where two caves erode back to back along the same line of weakness) 4. Undercutting of the arch occurs and the roof of the arch is weakened by weathering, eventually collapsing leaving a stack (column of rock isolated from the headland) 5. The stack continues to be eroded and eventually collapses forming a stump (covered at high tide).
Coastal Parn Yr.11
Coastline <ul><li>The coastline marks the meeting point between the land and sea. </li></ul><ul><li>This area is dynamic and constantly changing in nature due to the processes of erosion , transport and deposition that take place. </li></ul><ul><li>The extent of these processes are dependent on the amount of energy available. </li></ul><ul><li>At the coastline the energy source is the wind which transfers its energy to the water creating waves. </li></ul>
Wave <ul><li>Wind creates friction on the waters surface; </li></ul><ul><li>Frictional drag between the wind and the waters surface causes water particles to rotate and energy is transferred forward; </li></ul><ul><li>When the wave reaches shallow water, it slows down due to friction between the base of the wave and the sea bed. The shape of the wave becomes increasingly elliptical; </li></ul><ul><li>The top of the wave continues to move forward as it is unaffected by the friction with the sea bed. It becomes steeper and steeper and eventually breaks; </li></ul><ul><li>Water moves up the beach as the swash; </li></ul><ul><li>Water then returns back down the beach as the backwash. </li></ul>
Types of wave weak swash and strong backwash (beach is scoured and degraded as the strong backwash pulls sand and shingle back down the beach) strong swash and weak backwash (material is moved up the beach by the strong swash) lots of energy less energy steep gentle angle large in height small in height Destructive Wave Constructive Wave
Coastal Erosion Abrasion (corrasion) - when the sea throws rock up to hit the cliff, and break. Hydraulic Pressure - this is where erosion occurs due to the pressures exerted by breaking waves as air trapped in cracks in the cliff is compressed by the water. This compression and sudden release gradually forces the cracks apart. Solution (corrosion) - this is where salt water can act to dissolve some chemicals in the rocks, for example in limestone, calcium carbonate is dissolved, weakening the rock. Attrition - when the sea carries the rock to hit other rocks, making the rock break into small pieces.
Coastal Transport Weathering and erosion at the coast produces large amounts of material which is moved along the coast line and out to sea by the action of waves. <ul><li>Up and down the beach: </li></ul><ul><li>Material is moved up the beach in the swash and back down the beach in the backwash . </li></ul><ul><li>Constructive waves move large amounts of material up the beach as they have a strong swash, whereas destructive waves move large amounts of material down the beach due to their strong backwash. </li></ul>Movement of material along the coastline: LONGSHORE DRIFT The main movement of material at the coast is the movement of material along the coastline by the process of Longshore drift . <ul><li>Amounts of Longshore Drift depend on: </li></ul><ul><li>The strength of the waves </li></ul><ul><li>Size and amount of material available for the movement </li></ul><ul><li>Incline (slope) of the beach </li></ul>
Types of transportation There are four possible types of transport within the water: Solution - material carried dissolved in the water . Suspension - fine material carried suspended within the water itself Saltation - material which is too heavy to be continuously held in suspension is bounced along the sea bed. Traction - the heaviest material is simply rolled along the sea bed.
Coastal Deposition Features Although some material eroded at the coast is washed out to sea, most of the material is transported along the coast by longshore drift. Deposition will occur when the waves are now longer able to transport material due to a loss of energy. This is the case with constructive waves, where material is moved up the beach in the strong swash, but the weak backwash means material is deposited to build up the beach. <ul><li>Deposition commonly occurs : </li></ul><ul><li>where the water is sheltered (e.g. a bay) and the waves lack energy </li></ul><ul><li>where the coast is shallow and the increased friction between the water and the sea bed reduces the energy available for transport. </li></ul>Coastal Deposition Features : Deposition of material results in the formation of a number of distinctive features: beaches; spits; bars and tombolos.
Coastal Deposition Features: Beaches Beaches are the main features of coastal deposition. A beach is defined as the gently sloping area of land between the high and low water marks .
Coastal Deposition Features: Spits What are Spits? Spits are long narrow ridges of shingle and sand extending out into the sea or across a river estuary. <ul><li>Longshore drift moves material along the coastline. </li></ul>3.Over time, the spit grows and develops a hook if wind direction changes further out. 4.Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form. 2.A spit forms when the material is deposited.
Coastal Deposition Features: Bars What are bars and how are they created? A bar is formed where a spit continues to grow across a bay, creating a lagoon behind it . The lagoon, becomes an area of still water and a salt marsh forms in this low energy zone . Over time the lagoon will become infilled by deposition as either rivers flows in to it depositing material, or as waves break over the top of the Bar depositing coastal material
Coastal Deposition Features: Tombolo What are tombolo's and how are they created? Tombolo's are ridges of sand and shingle which join the mainland to an island . Tombolo's are created through the process of longshore drift . Where there is a change in the shape of the land, a spit forms in the shallow / sheltered water . A tombolo is formed where the spit continues to grow until it reaches an island, forming a link with the mainland .
Coastal Management Rapid coastal erosion often poses a threat to the settlement, industry and recreation that has grown up along the coast and we often look to protect the coast from erosion through appropriate management of the coastal system .
<ul><li>Less durable than a sea wall - may need replacing quicker </li></ul><ul><li>Don't give total protection to base of cliff </li></ul><ul><li>Environmentally ugly </li></ul><ul><li>Much cheaper than a sea wall </li></ul><ul><li>Effective at breaking the force of the waves </li></ul> Wooden structures break the force of the waves and trap beach material behind them <ul><li>Environmentally ugly (usually used in large numbers) </li></ul><ul><li>Effective where severe erosion and cheaper than sea walls </li></ul>Cages of boulders built into the cliff face - small rocks help to absorb the wave energy <ul><li>Environmentally ugly </li></ul><ul><li>Can be undermined and removed by waves due to washing away of sand and shingle beneath. </li></ul><ul><li>Relatively Cheap </li></ul><ul><li>Use natural materials / rocks </li></ul>Large boulders on the beach - lesson the force of the waves by absorbing the wave energy within the gaps between the rocks <ul><li>Most expensive </li></ul><ul><li>Deflected waves often scour the base, undermining the wall (may eventually collapse) </li></ul><ul><li>Sea walls reflect rather than absorb wave energy </li></ul><ul><li>Most effective means of preventing erosion </li></ul>Concrete Wall, curved under the side to deflect the power of the waves. Disadvantages Advantages How does it work? Method of Protection
<ul><li>can be expensive to keep transporting large amount of sand - sediment moved by longshore drift so will need frequent replenishment unless used with other defences </li></ul><ul><li>provides natural solution </li></ul><ul><li>provides natural solution </li></ul>Build up the beach by replenishing beach material, particularly at the base of structures to provide a 'natural' solution to absorbing wave energy. <ul><li>Can increase erosion further down coast by stopping longshore drift and starving areas further down coast of sediment. </li></ul><ul><li>Stops longshore drift encouraging the build up of the beach and effectively reducing erosion. </li></ul>Wooden or in some cases steel structures that stop longshore drift and build up / anchor the beach, protecting the base of a cliff Disadvantages Advantages How does it work? Method of Protection