coasts

• The coast is considered an open system that receives inputs from outside the system and transfers outputs away from the coast into other systems
• Coasts can be considered closed systems in some circumstances, such as during scientific research and coastline management planning
• The coastal system impacts and is impacted by processes in the five oceans and smaller seas
• Coasts can be split into sediment cells bordered by prominent headlands where sediment movement is almost contained and acts in dynamic equilibrium
• Dynamic equilibrium in a sediment cell refers to the balance in a natural system despite being in a constant state of change
• Inputs to the coastal system include marine (waves, tides, salt spray), atmosphere (sun, air pressure, wind speed and direction), and human activities (pollution, recreation, settlement, defences)
• Outputs from the coastal system include ocean currents, rip tides, sediment transfer, and evaporation
• Stores/sinks of sediment in the coastal system include beaches, sand dunes, spits, bars and tombolos, headlands and bays, nearshore sediment, cliffs, wave-cut notches, wave-cut platforms, caves, arches, stacks, stumps, salt marshes, tidal flats, and offshore bands and bars
• Processes that link inputs, outputs, and stores in the coastal system include wind-blown sand, mass-movement processes, longshore drift, weathering, erosion (hydraulic action, corrosion, attrition, abrasion), transportation (bedload, in suspension, traction, in solution), and deposition (gravity settling, flocculation)
• Energy sources driving transfers and flows in the coastal system include wind, gravitational, and flowing water
• The coastal system has negative feedback loops that lessen changes within the system and positive feedback loops that exaggerate changes, taking the system away from dynamic equilibrium
• Sediment sources to the coastal system include rivers, cliff erosion, wind, glaciers, offshore erosion, storm surges, tsunami waves, and longshore drift
• Sediment budgets assess gains and losses of sediment within a sediment cell, aiming to maintain dynamic equilibrium
• The littoral zone is the area between cliffs or dunes on the coast and the offshore area beyond the influence of waves, constantly changing due to short-term factors like tides and storm surges and long-term factors like sea level changes and human intervention
• The primary source of energy at the coast is from waves formed offshore, generated by wind, tectonic activity, or underwater landslides
• Factors affecting wave energy include strength of the wind, duration of the wind, and size of the fetch
• Wave types include constructive waves that deposit material and create depositional landforms, and destructive waves that remove depositional landforms through erosion
• The presence of constructive waves leads to steeper beach profiles favoring the formation of destructive waves, creating a dynamic equilibrium in beach profiles
• Dynamic equilibrium of a profile:

  • Profile is more gentle in summer and steeper during the winter months when destructive waves are more common
  • External factors like wind strength and direction can disrupt dynamic equilibrium
• Tides:

  • Gravity is a key source of energy in coastal environments
  • Tides occur due to gravitational pull of the sun or moon, leading to changes in water levels
  • Tidal range is the difference in height between tides, largest in channels like river estuaries
  • High and low tides are impacted by the positioning of the moon and sun
  • Spring tide occurs when sun and moon are in alignment, creating largest tidal range
  • Neap tide occurs when sun and moon are perpendicular, creating smallest tidal range
• Rip currents:

  • Powerful underwater currents near shoreline caused by plunging waves
  • Backwash forced under surface due to resistance from breaking waves, creating rip current
  • Riptides occur when ocean tide pulls water through small areas like bays or lagoons
  • Rip currents are an energy source in coastal environments, leading to sediment outputs
• High-energy and Low-energy Coastlines:

  • High-energy coastlines have powerful waves, rocky headlands, and frequent destructive waves
  • Low-energy coastlines have less powerful waves, sandy areas, and constructive waves
  • Different processes and landforms occur in high and low energy environments
• Wave Refraction:

  • Waves turn and lose energy around headlands on uneven coastlines
  • Wave energy focused on headlands, creating erosive features
  • Energy dissipated in bays, leading to formation of features associated with lower energy environments like beaches
• Erosion:

  • Erosion involves removal of sediment from coastline by different types of erosion
  • Main erosion processes: Corrasion, Abrasion, Attrition, Hydraulic Action, Corrosion, Wave Quarrying
  • Factors affecting erosion: Waves, Beaches, Subaerial Processes, Rock Type, Rock Faults, Rock Lithology
• Processes of Transportation and Deposition:

  • Transportation processes: Traction, Saltation, Suspension, Solution
  • Longshore Drift moves sediment along beach and between sediment cells
  • Deposition occurs when sediment becomes too heavy for water to carry, or when wave loses energy
• Weathering and Mass Movement Processes:

  • Weathering is breakdown of rocks over time, leading to transfer of material into littoral zone
  • Mechanical Weathering: Freeze-thaw, Salt Crystallisation, Wetting and Drying
• Chemical weathering involves the breakdown of rocks through chemical reactions
• Carbonation:

  • Rainwater absorbs CO2 from the air to create a weak carbonic acid
  • Carbonic acid reacts with calcium carbonate in rocks to form calcium bicarbonate, which can be easily dissolved
  • Acid rain reacts with limestone to form calcium bicarbonate, which is then easily dissolved allowing erosion
• Oxidation:

  • Minerals become oxidised when exposed to the air through cracks and fissures
  • Oxidation increases the volume of the mineral, contributing to mechanical weathering and causing the rock to crumble
  • Common oxidation within rocks is iron minerals becoming iron oxide, turning the rock rusty orange after exposure to the air
• Solution:

  • Rock minerals such as rock salt can be dissolved
• Biological weathering involves the breakdown of rocks by organic activity
• Plant Roots:

  • Roots of plants growing into the cracks of rocks exert pressure, eventually splitting the rocks
• Birds:

  • Some birds such as Puffins dig burrows into cliffs weakening them and making erosion more likely
• Rock Boring:

  • Many species of clams secrete chemicals that dissolve rocks
  • Piddocks may burrow into the rock face
• Seaweed Acids:

  • Some seaweeds contain pockets of sulphuric acid, which can dissolve some of the rock’s minerals when hit against a rock or cliff face (e.g. Kelp)
• Decaying Vegetation:

  • Water flowing through decaying vegetation and then over coastal areas becomes acidic, causing chemical weathering
• Mass movement is the movement of material down a slope under the influence of gravity
• Mass movement can be categorised into four main areas: creeps, flows, slides, and falls
• Factors influencing the type of mass movement include cliff/slope angle, rock type, rock structure, vegetation, saturation of ground, and presence of weathering
• Different types of mass movement include:

  • Soil Creep: slowest but most continuous form of mass movement involving the movement of soil particles downhill
  • Solifluction: occurs mainly in tundra areas where the land is frozen, forming solifluction lobes
  • Mudflows: increase in water content of soil reduces friction, leading to earth and mud flowing over underlying bedrock
  • Rockfall: occurs on sloped cliffs when exposed to mechanical weathering, leading to scree building up at the base of the slope