2.1. Wave, marine and sub-aerial processes Flashcards
Define wave
Waves are oscillation of the water surface
Water does not move forward
Define wave height/amplitude
The distance between the trough and the crest
Indication of wave energy
Define wavelength
The distance between successive crests or troughs
Define wave frequency
The number of waves per minute
Factors affecting the formation and size of a wave
- Wind velocity
- Depth of water
- Fetch - the distance of open water the wave travels over
What are the coastal zones?
- Upper beach/backshore - backed by cliffs or sand dunes
- Foreshore - periodically exposed by tides
- Offshore - covered by water
Define wave orbit
The shape of the wave. Varies between circular and elliptical. The orbit diameter decreases with depth (roughly equal to wavelength
Define wave base
When the orbit diameter decreases to a point there is no further movement related to wind energy
Define swell waves
Waves that are characterised by lower height and longer wavelength
Define wave breaker
Occurs when waves move further onshore, friction slows down the wave advance causing the shortening of wave
What are the 3 main types of breaker?
- Spilling breakers
- Plunging breakers
- Surging breakers
What are spilling breakers?
- are associated with gentle beach gradients and steep waves
- are characterised by gradual peaking of the wave until the crest becomes unstable => gentle pilling forward of the crest
What are plunging breakers?
- tend to occur on steeper beaches than spilling breakers with waves of intermediate steepness
- distinguished by the shore ward face of the wave becoming vertical, curling over and plunging forward
What are surging breakers?
- found on steep beaches with low steepness waves
- the front face and crest of the wave remain relatively smooth
- a large proportion of the wave energy is reflected at the beach
Define swash, backwash
- Swash: forward movement of water up the beach
- Backwash: backward movement of water down the beach
Define constructive waves/swell waves
- Swash is greater than backwash
- Large fetch
- Long wave length
- Low height
- Found on low gradient beaches, low energy waves which deposit materials
- Associated with spilling breakers
Define destructive waves/stom waves
- Backwash is greater than swash
- Short fetch
- Short wave length
- High waves and frequency
- Steeply sloping beaches
- High energy waves which erodes
Define tide
regular movements in the sea’s surface, caused by the gravitational pull of the moon and sun on the oceans
low spring tides occur just after a new moon
high spring tides occur after a full moon
Define tidal range
The difference between high and low tide
3 types of rides coastal areas can be classified into
- Microtidal - <2m
- Mesotidal - 2-4m
- Macrotidal - over 4m
Define storm surges
- changes in the sea level caused by intense low pressure systems and high wind speeds
- for every drop in air pressure of 10mb sea water is raised 10 cm
Define wave refraction
- is the change in speed and distortion of wave
- waves are refracted and energy is concentrated around headlands and more dispersed along beaches located in bays
- headland - converging waves, deeper waters (erosion)
- bay - diverging waves, shallower waters (deposition)
4 types of erosion
- Hydraulic action: water breaks against cliff face, air trapped in cracks and joints => cavitation
- Corrasion/Abrasion: process whereby breaking wave can hurl pebbles and shingle against a coast and thus abrading it
- Attrition
- Solution
Mass movements occur in coasts
- Salt weathering
- Freeze thaw weathering
- Biological weathering
- Solution weathering
- Slaking
