booklet three

• high energy coasts

  • strong prevailing winds create high energy waves
  • rate of erosion greater than rate of deposition
  • headlands, wave cut platforms, cliffs

  eg. Cornish coast
• what are the tides and what causes them?

  what are tides and what causes them?

  • the periodic rise and fall in sea level
  • caused by gravitational pull of sun and moon, moon has a greater influence as it is closer to earth
• spring tide

  • as moon orbits earth, high tide follows it
  • twice a lunar month, when earth, moon and sun are in straight line, the tide-raising force is strongest
  • produces the highest monthly tidal range or spring tide
• neap tide

  • twice a moth, moon and sun positioned at 90 degrees (perpendicular) to each other in relation to earth
  • this gives lowest monthly tidal range or neap tides
  • at this time high and low tides are between 10-30% lower than average
• how tides and waves influence coastal processes

  • the TIDAL RANGE affects the length of time that the littoral zone is exposed to subaerial weathering
  • the SPEED of incoming and outgoing tides has important scouring effect on coastline as strong currents can be generated

  CONSTRUCTIVE WAVES:DESTRUCTIVE WAVES:

  • small range results in deposition being concentrated on a narrow zone of the shore
  • with large range, zone of deposition is more dispersed
  • small tidal range means as waves break on shoreline, the wave energy is concentrated
  • large range means energy is more dispersed as tide ebbs and flows
• the shape of coast influences the tidal range

  the River Severn - a funnelled coast:

  • as tide advances its concentrated in the ever-narrowing space
  • causes height to rise rapidly producing a tidal bore
  • along River Severn this is referred to as the Severn Bore and is a wave of up to 1m in height, travelling at 30km an hour
• storm surges

  • occurs in intense low-level pressure systems from depressions and hurricanes
  • when water rises, it can lead to extreme flooding as strong winds push the water towards the shore
  • can creat vast amounts of damage on short amounts of time
• tidal ranges

  micro tidal ranges:meso tidal ranges:macro tidal ranges:

  • under 2 metres
  • 2 - 4 metres
  • over 4 metres
• pattern of tidal ranges

  • most places are meso or micro tidal ranges
  • you find macro tidal ranges on all continents, they are found on approx 10% of the earths surface
  • can find macro tides in SW Iceland, East China and on the UK coast
• The Bay of Fundy, Nova Scotia

  • highest tidal range in the world
  • 14 metre tidal range
  • natural oscillation corresponds with the times, creating huge amounts of energy for erosin
  • bay naturally funnels in and is shallow, adding to large tidal range
• low pressure

  • air rising creates winds
  • winds create waves
  • rain and winds, storms
• high pressure

  • air descends and cools
  • forms dry conditions
• longshore drift

  • waves pick up sediment and carry it to shore on the swash (along the coast)
  • backwash carries it back out to sea - directly down beach due to gravity
  • process repeats, transporting material along coast
  • quite an effective process, especially in formation of spits
• tidal currents

  • ebb currents are tidal currents that move away from the land
  • flow currents move towards the land

  should always be in equilibrium
• rip currents

  • a strong flow of water running from beach back to open ocean
  • can be more than 45 metres wide, most are less than 9 metres
  • can move at 8km an hour
  • can form in gap between sandbars
  • these underwater obstacles block waves from washing directly back to sea
  • feeder waves then run along shore until it finds an opening around the obstacle
  • the rip current rushes to the opening
• why do rip currents have limited impacts on the coast?

  they are localised and constantly shifting
• upwelling

  • movement of cold water from deep in ocean toward the surface
  • more dense cold water replaces warmer surface water
  • these currents form pattern of global ocean circulation currents
  • clockwise in northern hemisphere and anticlockwise in Southern Hemisphere
  • operate offshore so don't impact our coastlines