Coasts

• A spit is a narrow coastal landform that is elongated and extends into a body of water.
• Waves are marine processes that erode, transport, and deposit material
• Waves are formed by winds blowing over the surface of the sea
• Swash: Water rushing up the beach carrying shingles and sand
• Backwash: Water flowing back towards the sea dragging shingles and sand back out
• The energy of the swash and backwash determines the type of wave
• Constructive waves are beach builders with a long wavelength, low-frequency rate, and a shallow wave gradient
• In constructive waves, the swash is stronger than the backwash, depositing material onto the beach
• Destructive waves erode the beach with a short wavelength, high-frequency rate, and a steep wave gradient
• In destructive waves, the backwash is stronger than the swash, dragging material out to sea
• Factors affecting the rate of coastal erosion:

  • Large fetch of waves
  • Strong winds blowing for a long time creating destructive waves
  • Areas with no beach to buffer waves
  • Soft cliff material
  • Cliffs with many joints
  • Headlands where waves converge (wave refraction)
• Oceanic waves important terms:

  • Wave Height (H): vertical distance between crest and trough
  • Wavelength (L): horizontal distance between successive crests or troughs
  • Wave Period (T): time interval between the passage of successive crests
• Coastal erosion processes:

  • Hydraulic action: waves hitting a coastline, trapping air into cracks and joints, causing cliff splintering
  • Abrasion/Corrasion: sand and small pebbles wearing away shorelines and headlands
  • Attrition: waves causing rocks to knock into each other, becoming smaller pebbles, then sand
  • Solution: weak acidic chemicals in seawater reacting with rock chemicals, eroding the rock
• Sea Cliff Formation:

  • Waves erode a notch at the base of the cliff through hydraulic action, abrasion, and compressed air
  • When the notch is large enough, the overhanging rock collapses, forming a sea cliff
  • The cliff continues to retreat, creating a wave-cut platform visible at low tide
• Headlands and Bays:

  • Formed where soft rock erodes more quickly than hard rock (differential erosion)
  • Soft rock forms a bay, while hard rock forms a headland
• Sea Cave, Arch, Stack, and Stump Formation:

  • Strong waves erode cracks and weaknesses in the cliff base, forming a sea cave
  • Over time, a sea arch may form if the cave erodes through the headland
  • If the arch collapses, a sea stack remains, which may further erode into a sea stump
• Sea stack and Stump:

  • If a sea stack collapses into the sea over time, all that remains is a small stump of rock, known as a sea stump
• Blowhole:

  • A blowhole is a passage that goes through the roof of a cave to the land surface above
  • Formed when waves compress air that breaks a hole through the roof of the cave
• Coastal Erosion:

  • Different processes of coastal erosion can be described
• Features of Sea Deposition - Beach:

  • A beach is a gently sloping area of sand, shingle, or stones found between the high and low tide levels
  • Formed by the swash and backwash movements of the waves
• Features of Sea Deposition - Beach Formation:

  1. When waves break, they lose energy and drop the load. The swash carries this up the shore and deposits it.

  2. Backwash is weaker than swash, so it is unable to carry all of the deposited material back out.

  3. The heaviest material is deposited first. The finer material is carried closer to the shoreline.

  4. Over time, this material builds up to form a beach.

  5. In times of storm, the waves are stronger and can carry heavier material further up the shoreline to the high-tide mark, creating a storm beach
• Features of Sea Deposition - Sand Spit Formation:

  1. Longshore drift loses energy when interrupted by a sheltered bay.

  2. The material carried by longshore drift is then deposited.

  3. These deposits build up over time to gradually form a spit.

  4. The spit extends across the bay, and as it increases in size, vegetation grows on it
• Features of Sea Deposition - Sand Bar:

  • A sand bar is a narrow ridge of sand or shingle that seals off the mouth of a bay
  • A spit can grow in size until it completely seals off a bay, creating a lagoon behind it
• Features of Sea Deposition - Tombolo:

  • A tombolo is a narrow ridge of sand or shingle that joins an offshore island to the mainland
  • A spit can grow in length until it reaches a nearby island, forming a tombolo
• Longshore drift occurs when waves break at an angle to the coastline, causing sediment to be transported along the beach parallel to the shoreline.
• A coast with beaches and sand dunes has gently sloping shorelines consisting of sand and gravel accumulated by wind and wave action. Dunes can vary in height and shape.
• Wave action is the most common type of coastal erosion caused by waves breaking on the shoreline.
• Coastal erosion can lead to loss of land, damage to infrastructure, and changes in ecosystems.
• The rate of erosion depends on factors such as wave power (height and frequency), tidal range, and exposure to prevailing winds.
• Cliff retreat refers to the gradual movement of a cliff away from the sea due to erosion. It happens because the base of the cliff is being worn away faster than new rock is formed at the top.
• The formation of cliffs involves erosion caused by weathering, which breaks down rocks into smaller pieces. This process weakens the rock structure and makes it more susceptible to erosion by water and ice.
• The direction of longshore drift depends on the prevailing wind direction and the shape of the coastline.
• Spits can be formed from sand, gravel, or shingle depending on the availability of these materials along the coastline.
• Hard engineering solutions involve building structures like groynes, revetments, and sea walls to protect against coastal erosion.
• Soft engineering solutions aim to work with natural processes rather than against them, using techniques like beach nourishment, managed realignment, and salt marsh creation.
• Longshore drift occurs when waves approach the shore at an angle rather than directly perpendicular to the coastline.
• Sand spits are formed when sediment carried by waves accumulates along the shoreline, forming a narrow strip of land that extends out into the sea.
• Soft engineering solutions aim to reduce the impact of human activities on natural processes and promote sustainable management practices.
• Coastal defences are built to prevent flooding and erosion along the coastline.
• Beach management strategies include beach replenishment (adding sediment), beach stabilization (using vegetation), and beach renaturalization (restoring natural processes).