Sources of Energy in Coastal Environments- slides

• Coastal environments


  Created by 3 main types of processes: weathering, erosion, mass movement
• Weathering


  The breaking down or dissolving of rocks and minerals on Earth's surface creating regolith (loose material) that remains in situ until it is removed by erosional processes
• Types of weathering


  • Mechanical
  • Biological
  • Chemical
• Erosion


  The wearing away of the earth's surface by the mechanical action of processes of glaciers, wind, rivers, marine waves and wind
• Mass movement


  The movement of material downhill under the influence of gravity; may also be assisted by rainfall
• Sources of energy in coastal environments

  • Wind
  • Waves
  • Currents
  • Tides
• Wind


  A primary source of energy for some processes as well as being a type of erosion and transport in itself
• Wind


  • Spatial variations depend on strength and duration
  • Higher uninterrupted wind speeds = greater wave energy
  • Coastline affected by local weather patterns but this only influences short term changes
  • Coastline most affected by prevailing wind direction

  
• Fetch


  The distance of open water over which a wind can blow uninterrupted by major land obstacles
• Longer fetch = greater magnitude (size) of waves
• Waves are created by the transfer of energy from the wind blowing over the sea surface (known as frictional drag)

  
• Factors affecting wave energy

  • Strength of the wind
  • Length of time it is blowing
  • The fetch

  
• Wind erosion


  Wind can pick up sediment e.g. sand from the coast and use it to erode other features (abrasion)
• Waves


  The main agent in charge of shaping the coast
• Wave components


  • Crest
  • Wavelength
  • Trough
  • Wave height

  
• Wave breaking


  1. Base of wave slows down due to friction with seabed

  2. Crest carries on moving at same pace

  3. Crests start to jam up, shortening wavelength

  4. Waves get higher and eventually become top heavy and topple, breaking on the shore

  
• Swash


  The rush of water up the beach after a wave breaks
• Backwash


  The action of water receding back down the beach towards the sea
• Constructive waves


  • Low wave height
  • Long wavelength
  • Low frequency 6 to 8/min
  • Swash more powerful than backwash, more materials carried up and deposited on coast than removed

  
• Destructive waves


  • High wave height
  • Steep form
  • High frequency 10 to 14/min
  • Backwash stronger than swash, more sediment removed than added

  
• Most beaches subjected to alternating cycle of constructive and destructive waves
• Wave refraction


  Waves travel faster in deeper water, so if approaching coast at angle the side nearer coast in shallower water loses more energy to friction and slows down, causing wave to change direction

  
• Refraction around a headland can result in erosional formations on each side of the headland
• Longshore currents (littoral drift)


  Occur when waves do not hit the coast 'head on' but approach at an angle, resulting in a flow of water (current) along the shoreline that moves sediments along the beach

  
• Rip currents


  Strong currents moving away from the shoreline, develop when seawater is piled up along the coastline by incoming waves

  
• Upwelling


  Movement of cold water from the deep oceans to the surface, creating nutrient rich cold ocean currents
• Tides


  The periodic rise and fall of the sea level, caused by the gravitational pull of the sun and moon

  
• Causes of tides


  1. Sun and moon in line = Spring Tides

  2. Sun and moon at 90 degrees = Neap Tides

  3. Affected by seabed morphology, proximity of land masses, Coriolis effect

  
• Tidal range


  Difference in height of sea water at high and low tide, determines upper and lower limits of erosion and deposition, and amount of time littoral zone exposed to weathering

  
• Classification of tidal ranges

  • Microtidal (less than 2m)
  • Mesotidal (2 to 4m)
  • Macrotidal (more than 4m)

  
• Tidal/storm surges


  Formed when meteorological conditions give rise to strong winds which produce higher water levels than at high tide
• For every millibar the pressure drops the sea level rises by 1cm
• Strong winds drive water towards the coast and pile it up against the coast
• Storm surges are caused when deep depressions track east from the Atlantic, passing close to the north of Scotland
• The effect is enhanced by the strong northerly winds experienced on the rear flank of the depression as it continues eastwards
• High tides especially Spring Tides intensify the effect of storm surges