waves and beach morphology (2.B4A)

Question 1

beach sediment profile

Answer 1

the pattern of distribution of different sized or shaped deposited material.

Question 2

beach morphology

Answer 2

the shape of the beach

Question 3

how waves form

Answer 3

kinetic energy from prevailing winds creates friction against the waves causing energy to transfer into the sea creating a circular orbit of water.
!THE WATER ITSELF DOES NOT MOVE!
It is the energy that drives forward and moves forward forming beginning of a wave

Question 4

why do waves break?

Answer 4

• water becomes shallower
• waves encounter friction from sea bed slowing base of wave down
• closer to the shoreline, circular orbit changes to an elliptical shape: the crest moves faster than the base of the wave
• wavelength and velocity both decrease forcing the wave higher
• eventually, a critical point is reached: crest outruns the trough/ base and the wave topples= a breaking wave
• the water rushes up the beach as swash and can be further disrupted through backwash as it returns to the sea.

Question 5

constructive waves

Answer 5

are created offshore leading to a gradual increase in friction: gradually steepening wave front.

• low frequency (6-8 per minute)
• shallow gradient waves, long wavelength
• strong swash and weak backwash
• most common in summer
• strong swash constantly deposits material on the beach in an area called the berm which builds up the beach and is made up usually of shingle: steeper profile
• this leads to a sorting of material in the foreshore zone, with larger, heavier shingle (pebble-sized sediment) at the back of the beach, and sand drawn back closer to the sea.
• AND since the backwash flows down the beach and loses energy, sediment is further sorted as coarser sands are deposited in the middle of the beach and only fine sands are carried to the area of beach closest to the sea.

Question 6

destructive waves

Answer 6

are created as a result of locally generated waves and increased frequency results in steep circular plunger waves

• high frequency (10- 14 per minute)
• high energy, short wavelength
• weak swash, strong backwash
• most common in winter: berms built up in summer are eroded by plunging waves creating a GENTLE profile
• the strong backwash transports large, pebble-sized sediment which is dragged down beach and deposited to form wide ridge of material below low tide mark: the start of an offshore bar/ zone
• friction may be sufficient to cause backwash to down some sediment on middle or lower beach, with deposited sediment size decreasing towards sea.
• storm beaches can also form: result of destructive waves flinging material at the very back of the beach profile where the backwash does not reach: sediment here is made up of much larger angular rocks.

Question 7

daily variation

Answer 7

• storm events during summer will produce destructive waves that reshape beach profile in a few hours.
• destructive waves change to constructive ones as the wind drops.
• daily tides (though do not have as much effect as monthly tides)

Question 8

monthly variation

Answer 8

• tide height varies over course of lunar month, with highest high tide occurring twice a month at spring tide (sun, moon and earth all aligned therefore gravitational pull= strongest) and two very low high tides (neap tides)​ (sun and moon at right angles, weakest pull)

changes that occur as a result:

• as month progresses from spring down to neap tide, successively lower high tides may produce a series of berms at lower and lower points down the beach.
• once neap tide passes and move towards next spring tide, berms successively destroyed as material pushed further up beach by rising swash reach.

Question 9

seasonal variation

Answer 9

• destructive, high-energy waves dominate in the winter, lowering angle of beach profile and spreading shingle over the whole beach. offshore ridges/bars formed by destructive wave erosion and subsequent deposition of sand and shingle offshore.
• in summer, constructive, low-energy waves dominate, steepening beach angle and sorting particles by size, with larger shingle particles towards back of beach. ​​In summer, constructive waves build berm ridges, typically of gravel/shingle at high tide mark
• low channels and runnels between berms

Question 10

decadal variation

Answer 10

• climate change is expected to produce more extreme weather events in the UK

as a result:

• winter profiles may be present for longer time over course of year
• more frequent and more powerful destructive waves may reduce beach size, allowing high tides to reach further inland and increasing rate of coastal erosion in what was backshore zone.