2.1. Wave, marine and sub-aerial processes Flashcards Preview

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Flashcards in 2.1. Wave, marine and sub-aerial processes Deck (39)
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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


Salt weathering

the process by which sodium and magnesium compounds expand in joints and cracks thereby weakening rock structures


Freeze-thaw weathering

The process whereby water freezes, expands and degrades jointed rocks


Biological weathering

carried out by molluscs, sponges and sea urchins that burrow


Solution weathering

the chemical weathering of calcium by acidic water



materials disintegrate when exposed to water


Energy factors affecting the rate of erosion

  • Waves - wave steepness (steep destructive waves have more erosive power) and wave breaking point (where wave break at cliff base that cause maximum erosion)
  • Tides
  • Currents
  • Winds - onshore winds erode fine beach material, offshore winds erode dunes