Coastal Landscapes

• A coastline is where the land meets the sea. Coastlines are shaped by a number of different coastal processes. Coastal processes are a sequence of events taking place along the coast.
• There are two types of waves:

  Destructive waves

  Constructive waves
• Height and strength of waves are influenced by several factors:

  Wind speed

  Wind duration (how long the wind blows for)

  Fetch (distance over water that the wind blows in a single direction)
• Destructive waves are responsible for erosion
• Constructive waves are responsible for deposition
• Destructive waves:

  
• Constructive waves:

  
• Physical processes- Erosion

  • Abrasion- Sand and pebbles carried within waves are thrown against the cliff face. These particles break off more rocks, which, in turn are thrown against the cliff by the breaking waves.
• Physical processes- Erosion

  • Hydraulic action-Pressure of the water being thrown against the cliff by the wave. Also includes the compression of air in cracks; as the water gets into the cracks in the rock face, it compresses the air in the cracks, this puts even more pressure on the cracks and pieces of rock break off.
• Physical processes- Erosion

  • Solution- A chemical reaction between certain rock types and the salt and other acids in seawater.
• Physical processes- Erosion

  • Attrition- Wearing away of rocks that are in the sea. As the boulders in the sea continually roll around, they chip away at each other until smooth pebbles or sand are formed.
• Weathering is also responsible for shaping coastlines. Weathering is the breaking down of rocks. There are 3 main types of weathering.
• Weathering:

  • Mechanical (physical)- Occurs when rocks are broken down by physical factors in the environment e.g. wind, water, temperature change.
• Weathering:

  • Chemical- Rainwater contains weak acids that can react with certain rock types.
• Weathering:

  • Biological- The action of plants and animals on the land. Seeds that fall into cracks in rocks will grow when moisture is present. The roots of the plant forcw their way in, and, in time can break up rocks. Burrowing animals, such as rabbits can also be responsible for the further break-up of rocks. This is due to the way they tunnel; through the upper layers of the soil.
• Mass movement is when material moves down a slope due to the pull of gravity. On coastlines, slumping and sliding occur. This can cause coasts to retreat rapidly.
• Physical processes- Mass movements:

  Slides- Material shifts in a straight line (sliding)

  Slumps- Material shifts with a rotation (slumping)
• Waves also transport eroded material along the coast. There are many ways material is transported: traction, saltation, suspension, solution and longshore drift.
• Longshore drift is a type of transportation responsible for moving a lot of material down the coastline.
• Longshore drift process; The direction of the waves hitting the coastline is determined by the prevailing wind. If the wind is blowing at an angle to the beach, the waves (swash) will approach the beach at this angle, transporting the sand and pebbles with them. As the returning wave (backwash) is being pulled by gravity, it will take the shortest route back down the beach, and it also takes the pebbles with it. It always goes back down the beach in a straight line at 90 degrees to the coast. In this way, material is moved along the beach until it meets an obstruction.
• Geology influences coastal recession, the process in which erosion and weathering causes cliffs to recede inland.
• The speed at which a cliff is eroded or recedes is called the rate of cliff recession.
• Hard rocks, like granite, are more resistant, so it takes longer for them to e eroded and weathered by physical processes. This creates steep cliffs.
• Softer rocks, like clay and chalk, are less resistant, which means they are eroded more quickly creating gently sloping cliffs.
• Joints and faults are cracks and weaknesses in the rock. rocks with lots of joints and faults erode faster.
• Joints are small, natural cracks, found in many rocks.
• Faults are larger cracks caused in the past by tectonic movements.
• The more joints and faults there are in a cliff, the weaker the cliff will be. Hydraulic action attacks faults and joints, causing erosion.
• Coastlines where the geology alternates between bands of hard rock and soft rock are called discordant coastlines. They lie at right angles to the sea.
• A concordant coastline has the same type of rock along it's length, parallel to the coastline.
• Bays and headlands form along the coast, where there are alternating bands of hard and soft rock.

  The sea erodes the soft rock faster than the hard rock, forming a bay.

  The hard rock forms a headland sticking out into the sea.
• Weather in the UK varies with seasons (seasonality). Temperatures are coldest in winter, warm through spring, hottest in summer. then cool through autumn.
• Impact on coastal erosion/retreat:

  • Weather- Differences in temperature have an impact on processes along the coast. For example, mild temperatures increases the rate of salt weathering (seawater in cracks --> when water evaporates salt crystals form --> expand and put pressure --> causing break-up) because water evaporates more quickly. This can alter the landscape e.g. weathering looses material which leads to mass movement. The differences between day and night temperatures can cause freeze-thaw weathering on cliff faces.
• Impact on coastal erosion/retreat:

  • Storms- strong wind creates high energy destructive waves which increase erosion of cliffs and cause coastal recession. Intense rainfall can cause cliffs to become saturated, making mass movement more likely.
• Impact on coastal erosion/retreat:

  Prevailing wind- Determine the direction of longshore drift, affecting where deposition happens Also affect whether a coastline is exposed to storms. More exposed coasts are more vulnerable to erosion and coastal retreat.
• Impact on coastal erosion/retreat:

  Seasonality- Differences between day and night temperatures can cause freeze-thaw weathering. Storm waves are powerful agents of erosion. Prevailing winds can have a long fetch; the longer the fetch, the stronger the wind and the more powerful the wave, and the faster the rate of erosion.
• Strong winds and storms create high energy, destructive waves leading to erosion.
• Global warming leads to higher sea-levels because a warmer climate causes seawater to expand and also causes the ice sheets and glaciers to melt, leading to increased sea levels as a result.
• The likely effects of sea level rise on the UK are: cliffs that are currently being undercut and collapsing will continue to retreat. Areas of soft coastline may experience more erosion and retreat due stronger and more frequent storms.
• A storm surge is a large-scale increase in sea level (up to 3 metres around the UK) as gale-force winds drive water towards the coastline.