physical factors - waves Flashcards
where do waves come from?
the frictional drag of the wind moving over the ocean surface, the forward movement of energy NOT water. circular movement of individual water molecules
what happens when a wave enters shallow water?
as the wave enters shallow water the deepest circling molecules have contact with the seabed + friction slows the wave.
* the bottom part of the wave slows faster than the top, so the wave steepens and the crest advances ahead of the trough and topples over and breaks
* at this point = a significant forward movement of water as well as energy
what are storms waves?
- form close to shore
- more energy
- shorter wave period (5 seconds)
- short wavelength
- great height
what are swell waves?
- form out to sea
- formed in open oceans
- can travel huge distances from where generated
- wave period = 20 seconds
what is swash?
moves up the beach in direction of wind, driven by transfer of energy that occurs when wave breaks
what is backwash?
moves back down at right angles to the shore due to gravity
how does backwash work with breaking waves?
as wave breaks speed of water decreases as it travels up the beach due to friction + uphill gradient = loses energy and once no more energy to move forwards = drawn back down as backwash
what are spilling waves?
steep waves breaking onto gently sloping beaches –> spills gently forwards
what are plunging waves?
steep waves breaking onto steep beaches, water plunges VERTICALLY downwards as crest curls over
what are surging waves?
low-angle waves breaking onto steep beaches; wave sides forward may not break
what are constructive waves?
they DEPOSIT sediment strong swash travel long way up the beach, swash loses volume + movement = weak backwash + low sediment movement off the beach
how do constructive waves retain energy?
due to long wavelength, backwash returns to sea before next wave breaks, and next swash movement is uninterrupted and so it retains its energy = so swash energy EXCEEDS backwash energy
features of constructive waves?
- low in height
- long wavelength
- low frequency (6-8 per min)
- usually break as spilling waves
what are destructive waves?
REMOVE sediment, friction from steep beach slows the swash and doesn’t travel far before returning as. backwash = swash energy is LESS than backwash energy
features of destructive waves?
- greater height
- higher frequency (12-14 per min)
- shorter wavelength
- remove sediment = form storm beaches
- break as plunging waves = little forward transfer of energy
factors that affect beach gradient and wave type relationship
- angle of wave approach
- wave steepness
- sediment particle size
how do high energy waves affect beach gradient?
- high energy waves occur in winter months
- remove material from top of beach and transport it to offshore zone = reducing beach gradient
how do low energy waves affect beach gradient?
- low energy waves occur in summer months
- build up beach face = steepening profile
what is fetch?
the distance of the sea, over which the wind has travelled uninterrupted
what is wavelength?
the distance between 2 successive crests
what is wave frequency?
number of waves per minute
what is wave height?
the distance between the crest and trough
what energy do waves posses?
posses POTENTIAL energy as result of its position above the wave trough and KINETIC energy caused by motion of water within the wave
