1.1.8 Variations in coastal processes, landforms and landscapes

Changes in seconds:

• High energy storm events

  • A storm event or tsunami causes an increase in wave energy, resulting in increases in erosions and transportation, which can cause:

    • Removal of large amounts of beach sediment, changing the profile or removing it all together

    • Destruction or breaching of sand dunes

    • Coastal flooding

• Rapid mass movement

  • Sudden rockfalls, landslides and slumps create changes in cliff-face profiles and retreating cliffs, with the loss of land and possibly buildings

Seasonal changes:

• Changes to the beach profile:

  Summer	Winter
  Fewer storms	More storms
  Less frequent high wind speeds	High winds more frequent
  Lower energy waves	Higher energy waves
  Waves predominantly constructive	Destructive waves more frequent
  Sediment moved onshore, building up the beach, increasing the gradient of the upper beach and forming a berm	Sediment moves offshore, lowering the beach profile, creating a steeper upper beach and a gentler lower beach

Changes over millennia:

• Sea level change:

  Eustatic change	Isostatic change
  A global change in th volume of water in the oceans	A localised change in the relative sea level caused by the upward or downward movement of land masses
  During a glaciation period more water is frozen, resulting in less liquid in the oceans, so sea level falls	During glacial periods the weight of ice causes the land to sink into the crust, making sea levels appear relatively higher
  Global warming of the climate increases melting of continental ice sheets, adding water to the oceans and raising sea level	Melting ice removes the weight anf the land very slowly rises, causing a relative fall in sea level (isostatic recovery)
  Warming of the oceans results in the volume of water expanding, creating a rise in sea level

The impact of rising sea levels on landforms:

• Rising sea levels flood lower-lying parts of the coast

• Deltas, spits and beaches disappear underwater or due to increased rates of erosion

• River floodplains and valleys form a broad river estuary known as a ria, for example the kings bridge estuary in Devon

• If the flooded valley is a glaciated U-shaped valley, a fjord is formed

  • The shape of the valley means fjords are very deep, flat bottomed and steep sided, for example Sognefjord in Norway, which is 204km long and 1308m deep

  • Fjords often have a shallower entrance known as a threshold, formed as the glacier had less erosive power when the ice met the sea, or when the glacier deposited a terminal moraine. If the sea level ride does not cover the threshold, a small rocky island called a skerry will be created. Many of the islands off the coast of Norway are skerries, linked to 1190 fjords along the coast

The impact of falling sea levels on landforms:

• Beaches are no longer affected by waves and are left stranded above the new sea level, forming raised beaches

• The former cliff line and landforms are left stranded as relict cliffs, which are no no longer undercut and over time become degraded cliffs due to sub-aerial processes, and covered in vegetation

• The wave-cut platform appears raised above the new sea level to form a marine terrace, which can be used for aggriculture

• These features can be found along the western coast of Scotland, where the rate of isostatic recovery is around 2mm a year