Coastal Landscape Development

• Cliffs and wave-cut platforms

  When waves break against the foot of a cliff, erosion (hydraulic action and corrosion in particular) tends to be concentrated close to the high-tide line. This creates a wave-cut notch. As the notch gets bigger, the cliff is undercut and the rock above it becomes unstable, eventually collapsing.

  As these erosional processes are repeated, the notch migrates inland and the cliff retreats, leaving behind a gently sloping wave-cut platform, which is usually only completely exposed at low tide.
• Steep cliffs tend to occur where the rock is strong and resistant to erosion, such as most igneous and metamorphic rocks. Sedimentary rocks that are dipping steeply or even vertically tend to produce steep and dramatic cliffs.
• Gentle cliffs usually reflect weak or unconsolidated rocks that are prone to slumping. Rocks that are dipping towards the sea also tend to have low-angle cliffs.
• Horizontal strata produces steep cliffs
• Caves, Blowholes and Arches

  • The erosion of rocks like limestone and chalk tends to exploit any lines of weakness – joints, faults and cracks.
  • When joints and faults are eroded by hydraulic action and abrasion, this can then create caves. If the overlying rock then collapses, a blowhole will develop.
  • If two caves join up, or a single cave is eroded through a headland, an arch is formed. The base is widened and the gap is further enlarged by erosion and weathering
• Stacks and Stumps

  • Eventually, the top of the arch collapses leaving an isolated pillar of rock called a stack. As it continues to be eroded by the sea, the stack collapses to leave a stump, which may only appear above the surface at low tide.
• A beach can be described as a depositional landform extending from approximately the highest high tide to the lowest low tide.
• Beach accretion will take place during a prolonged period of constructive waves driven by storms many hundreds of miles away.
• Swash-aligned beaches tend to form in low-energy environments such as bays that are affected by waves arriving roughly parallel to the shore. . The bayhead beach may consist of either sand or shingle, depending on factors like the nature of the sediment and the power of the waves.
• Drift-aligned beaches form where the waves approach the coast at an angle. Longshore drift moves sediment along the beach, often culminating in the formation of a spit, essentially a sediment sink or store. Sediment may be graded along a drift-aligned beach.
• Beach Zones

  Backshore, foreshore, nearshore, offshore
• Beach profiles are steeper in summer, when waves are more constructive than destructive.
• In winter, destructive waves occur at a higher frequency (11 - 16 per minute). Berms may be eroded by plunging waves and high-energy swash crashing down onto the beach. Strong backwash transports sediment offshore.
• Spits

  Sand or shingle is moved along the coast by longshore drift, but if the coastline suddenly changes direction (e.g. because of a river estuary), sediment begins to build up across the estuary mouth and a spit will form. The end of the spit will also begin to curve round, as wave refraction carries material round into the more sheltered water behind the spit. This is known as a recurved tip
• Tombolo

  A tombolo is a beach (or ridge of sand and shingle) that has formed between a small island and the mainland. Deposition occurs where waves lose their energy and the tombolo begins to build up.
• Offshore Bars

  Submerged (or partly exposed) ridges of sand or coarse sediment created by waves offshore from the coast. Destructive waves erode sand from the beach with their strong backwash and deposit it offshore.
• Barrier beach (bar)

  Where a beach or spit extends across a bay to join two headlands, it forms a barrier beach or bar. These can trap water behind them to form a lagoon. Where a beach becomes separated from the mainland it becomes a barrier island e.g. Lido of Venice
• Conditions requires for a sand dune to form are

  • large quantities of available sand, washed onshore by constructive waves (an offshore sand bar is an ideal source of sand)
  • large tidal range, creating a large exposure of sand that can dry out at low tide
  • dominant onshore winds, that will blow dried sand to the back of the beach.
• Sand Dune Stages

  Embryo dune, fore dune, yellow dune, grey dune, dune slack, mature dune (climax community)
• Soil pH becomes more acidic as sand dunes success
• At river estuaries, most of the sediment accumulating is mud, due to the low velocity, Overtime, mudflats form and can develop into salt marshes.
• Salt marshes develop in three types of environment

  • In sheltered areas where deposition occurs.
  • Where salt and freshwater meet.
  • Where there are no strong tides or currents to prevent deposition and accumulation.
• Salt Marsh Formation (1)

  • Mud is deposited close to the high-tide line, dropping out of the water by a process known as flocculation. This involves the tiny individual particles of clay (mud) sticking together and sinking.
  • Pioneer plants such as eelgrass and cordgrass start to colonise the transition zone between high and low tide. These plants are halophytes and they also help to trap further deposits of mud.
• Salt Marsh Formation (2)

  • Mud level rises above high tide and a lower saltmarsh develops with a wider range of plants that no longer need to be so well adapted to salty conditions.
  • Soil conditions improve and the vegetation succession continues to form a meadow.
  • Mud levels rise and creek systems develop that deepen as the marsh becomes higher, saltwater gets trapped and evaporates, increasing salinity.
  • Eventually, shrubs and trees will colonise the area as the succession reaches its climatic climax as land rises above sea level.
  • e.g. Morecambe salt marsh
• eustatic change – when the sea level itself rises or falls
• isostatic change – when the land rises or falls, relative to the sea.
• Isostatic change occurs locally. During glacial periods, the enormous weight of the ice sheets (which can be several kilometres thick) makes the land sink – isostatic subsidence. As the ice begins to melt at the end of a glacial period, the reduced weight of the ice causes the land to readjust and rise – isostatic recovery.
• Land in the north and west of the UK (which was covered by ice sheets during the last Ice Age) is still rising as a result of isostatic recovery.
• Land in the south and east of the UK (which the ice sheets never covered) is sinking. Rivers pour water and sediment into the Thames Estuary and the English Channel. The weight of this sediment causes the crust to sink and relative sea levels to rise.
• The uplift of mountain ranges and coastal land at destructive and collision plate margins that resulted in a relative fall in sea level in some parts of the world.
• Local tilting of land at destructive margins, for example, some ancient Mediterranean ports have been submerged and others have been stranded above the current sea level.
• A fall in sea level exposes land previously covered by the sea, creating an emergent coastline.
• A rise in sea level floods the coast and creates a submergent coastline.
• Raised beaches (an emergent landform) are common on the west coast of Scotland, where the remains of eroded cliff lines (called relic cliffs) can often be found behind the raised beach, with wavecut notches and caves as evidence of past marine erosion.
• Rias (sheltered winding inlets with irregular shorelines) are one of the most distinctive features associated with a rise in sea level. They form when valleys in a dissected upland area are flooded, but the higher levels remain dry e.g. Kingsbridge estuary in south Devon
• Fjords are formed when deep glacial troughs are flooded by a rise in sea level. They are long and steep-sided, with a U-shaped cross-section and hanging valleys. Unlike rias, fjords are much deeper inland than they are at the coast. The shallower entrance marks where the glacier left the valley e.g. Sogne Fjord in Norway
• Dalmatian coasts are distinctive submergent coastlines that form in a landscape of ridges and valleys running parallel to the coast. When the sea level rises, the valleys flood, although the tops of the ridges remain exposed, forming a series of offshore islands running parallel to the coast.
• The IPCC estimates that by 2100 sea levels could rise by between 30 cm and 1m from current levels.
• Sea level rise is the result primarily of thermal expansion of water, due to heating, and the melting of freshwater ice, such as the Greenland and Antarctic ice sheets and mountain glaciers.
• The first dunes to develop are known as embryo dunes. They are suitable for colonisation by grasses. These are able to grow upwards through the accumulating wind-blown sand, stabilising the surface