Waves and Tides – Key ideas by hcj

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									                               Waves and Tides – Key ideas

Waves
1. What are waves? – link to:
http://www.mos.org/oceans/motion/wind.html

    A wave is a way in which energy travels from one place to another
    The highest point the waves reaches is called the crest.
    The lowest point is called the trough.
    The distance from one crest to the next is the wave length.
    The number of waves that pass a given point in one second is the wave's frequency.




 When wind blows over the ocean's surface, it creates waves. Their size depends on how far,
     how fast and how long the wind blows.

    In the open sea, waves make floating boats bob up and down instead of pushing them along.
     This is because the waves travel through water, the do not take the water with them.
     As a wave arrives it lifts water particles. These travel forward, then down and back so that each
     particle completes a circle.
     Circling movements of particles near the surface set off smaller circling movements below
     them.




    Using the diagram above and page 24–describe how the wave looks as it reaches
    the coastline.




2. Classifying waves

    Destructive - plunging breakers
    Constructive – spilling breakers
    What is the effect of different waves on a coastline? (mention swash and
    backwash)




3. The strength of waves

 Fetch, wind direction and strength are the main factors in determining the height and
     energy of breaking waves


      Long fetch =


      Which winds blow with the greatest frequency and strength?

        What type of winds do we get in the UK?




4. Wave refraction
 As waves approach the shore the water depth alters their angle of approach.
 The new concentrations of energy affect erosion
 Often headlands have concentrated energy


5. Currents
    Rip currents are fast moving areas of backwash channelled into beach runnels or
     depressions.
    They increase erosion locally by concentrating currents of water into narrow channels
     which are then scoured deeper –
    These channels can interrupt incoming breakers.
    They can be dangerous to swimmers
Tides

6. http://www.mos.org/oceans/motion/tides.html

   Tide-generating forces are a result of the gravitational attraction between the Earth,
    sun, and moon.

   The pull results in 2 large bulges in the oceans in line with the moon and sun
   The bulges move around the earth as it rotates giving two high tides per day
   Spring and Neap tides occur once a month




 Tidal range varies significantly – Mediterranean = small, Bristol channel = large
 A high tidal range leads to a broad zone of wave attack on cliff faces - wave cut
  platforms can result
 Phenomena such as the Severn bore can occur

 Tides affect the physical and economic geography of coasts, and have a profound
    effect on ecosystems

7. Storm surges

 A combination of conditions such as high tide, strong winds, long fetch, pressure
  changes can cause a storm surge
 If the area it hits is low lying and populated it can have devastating effects

 Make a case study of the North sea storm surge of 1953

								
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