Coastal areas section 1

Question 1

Describe wave motion towards shore

Answer 1

• As wave approaches shore, depth of water becomes shallower -> wavelength and velocity decrease -> mode of movement changes dramatically
• Top waves want to move fast but bottom waves need to overcome friction with seabed
• Friction interferes with the circular orbital movement of the water
• Hence, wave height increases and steepens
• Eventually, the circular motion becomes more elliptical as sea floor starts to interfere with it
• Wave - over-steepened, eventually breaks as its crest crashes forward / topples creating surf, where wave height is equal to wave depth

Question 2

How To measure wavelength

Answer 2

Measure wave period
Measure 10 wave crests and troughs
Record time taken for 10 wave crests to pass the ruler
Calculate wave period, T (in seconds), which is the time taken for one complete wave to pass a point
T = (time taken for 10 wave crests to pass a ruler) / 10
Wave length (in m) = 1.56 * T^2

Question 3

Factors determining wave energy

3

Answer 3

Wind velocity
Strong winds exert greater frictional drag, hence bigger waves

Wind duration
The longer the wind, the larger the waves

Length of fetch
distance of open water over which wind blows or the waves travel
Longer fetch generates higher energy waves

Question 4

Spilling breakers

characteristics (2)

Answer 4

Occur on beaches with gentle slopes

Break far from the shore

Question 5

Plunging breakers characteristics (4)

Answer 5

Happen on beaches where the slope is moderately steep
Normally curls over, forming a tunnel until the wave breaks
Exerts considerable force
Surfer waves

Question 6

Surging breakers characteristics (4)

Answer 6

Happens on beaches where the slope is very steep (sudden, powerful, forward / upward movement)
Wave does not actually break because base moves fast
Rolls onto the steep beach
Destructive nature because of the backwash

Question 7

Constructive wave characteristics

Gradient
Energy environment
Wave Height
Wave length
Wave frequency
Swash comparison to backwash
breakers type
Where it occurs
Coastal process

Answer 7

Low gradient
Low energy environment
Low wave height
Long wave length
Wave frequency: low
Swash more powerful than backwash 
Swells and spilling breakers
Occurs on gentle coastal slope and sheltered coast
Deposition

Question 8

Why constructive waves have a stronger swash than backwash

Answer 8

constructive waves gains a little height, breaks and spills on beach. Water spreads a long way to the gently sloping beach, resulting in a strong swash

Question 9

Destructive wave characteristics

Gradient
Energy environment
Wave Height
Wave length
Wave frequency
Swash comparison to backwash
breakers type
Where it occurs
Coastal process

Answer 9

High gradient
High energy environment
High wave height
Short wave length 
Wave frequency: 10-14 per min
Backwash more powerful than swash
Plunging and surging breakers
Occurs on steep coastal slope and open coast
Erosion

Question 10

Describe wave refraction (4) and explain what happens when it converge/diverge on headlands and bays (4)

Answer 10

Process by which waves change direction when they approach a coast
Occurs only when there is friction between water and seabed
Change in wave speed and wavelength (as waves pass from one medium to another)
Waves travel faster on the surface of deep water than they do on shallower water
Waves converge on headlands and diverge on bays
When waves converge - increased wave height and greater erosive energy
When waves diverge - decreased wave height and lower erosive energy
Results: Uneven impact on shoreline

Question 11

Where are headlands formed (4)

Answer 11

Most likely found in areas of alternating resistant and less resistant rock
Less resistant rocks experience more erosion as rocks are more susceptible to erosion -> develop into bays over time -> more resistant rocks stand as outcrops called headlands

Sheltered bays experience low energy breakers, which encourage accumulation of sediments to occur to form beach

Question 12

What happens at headlands

Answer 12

When waves move into shallow water at headland, “feel bottom” and hence velocity decreases
Waves in deeper water continue to move quickly (moving towards bay)
Waves bend near headland -> they wrap in and push together at headland -> wave energy concentrates at headland -> biggest waves and greatest erosion

Question 13

What happnes at bays

Answer 13

Waves keep moving fast towards bay
Waves are lower and less steep than those at headland
Wave energy gets spread out on the deep bay
Energy dissipated nearing shore -> smaller waves -> weaker erosion at bay

Question 14

What does wave erosion refer to

Answer 14

Refers to the breaking down and wearing away of land, resulting in long term removal of beach sediments by wave action, tidal currents, wave currents

Question 15

Hydraulic action (C3E1)

Answer 15

Cause 
  Waves striking against a rock 
  surface trap air in its joints
  This air is compressed by the 
  oncoming waves
  Exerting pressure on the joints
Effect
  These joints weaken and the rocks 
  shatter over time

Question 16

Abrasion (c3e1)

Answer 16

Cause
As waves break, sediments carried by waves such as sand and rocks are hurled against the coast
These loosened sediments knock and scrape against the coastal cliffs
This weakens the surface, resulting in the breaking down of the coast

Effect
Over time, the impact from abrasion is powerful enough to undercut a cliff

Question 17

Attrition (C+E)

Answer 17

When rock particles carried by waves rub or hit against one another, they break down into smaller pieces and become smoother and more rounded over time

Question 18

Solution (C2E1)

Answer 18

Cause
Sea water reacts chemically with water-soluble minerals in coastal rocks and dissolves them
eg. limestone rocks are easily eroded by carbonic acid in solution

Effect
When solution of minerals occurs, rocks are weakened and will eventually disintegrate

Question 19

Formation of a notch, cliff and shore platform (4)

Answer 19

Wave energy at its maximum at the foot of a cliff (wave refraction) results in undercutting of the base of cliff to form a wave-cut notch
Continual undercutting by waves at the base of the cliff will continue -> which increase stress and tension, resulting in enlarged notch
Weight of overhanging cliff causes it to collapse over time, cliff retreats inland, with eroded materials being deposited at its base
Processes repeat and eroded materials are carried away by waves, leaving behind a gently sloping platform at the base of the cliff -> wave-cut platform

Question 20

Chartacteristicsof spit (2)

Answer 20

Long narrow accumulation of sand or shingle

One end joined to the mainland and the other projecting out to sea or extending part way across a river estuary

Question 21

Formation of tombolo (1)

Answer 21

Tombolo is a beach that extends outwards to join an offshore island

Question 22

Formation of bar

Answer 22

Bar develops when a spit forms in a bay where there is no major river flows, may be able to build across the bay to join 2 headlands over time
Bars straighten coastlines and trap water in lagoons on the landward side

Question 23

Essential conditions for spits / tombolos to develop (6)

Answer 23

Essential conditions for spits / tombolos to develop
Presence of rock particles / sediment (enough deposits to rise above the water)
Larger materials
Presence of longshore drift
Coastline bends
Slack water (low energy environment)
Vegetation to take root and stabilise the land

Question 24

Formation of sand dunes (4)

Answer 24

Once sand has been deposited on a beach by waves, it is transported by the prevailing winds
The sand gradually migrates landward
Shallow slopes of sand form, grains move up the slope and are dropped on the steeper lee (“protected”) side of the pile, where the wind velocity is lower
After some time, these dunes will be covered with vegetation (eg. Marram grass) that help to stabilise them and encourage more sand to pile up

Question 25

Formation of spit (8)

Answer 25

Waves breaking obliquely at the shore move materials along the shore in a zig-zag manner by swash and backwash (beach drift) along the seabed parallel to the coast by longshore currents

Spits may be stabilised by vegetation

This combined lateral movement of materials (longshore drift) does not change direction when the coastline bends or when the coast has a bag

Continue to transport materials in the original direction

Due to continuous longshore direct, a narrow accumulation of beach materials that extends from the coast is formed, called a spit

The spit may increase in length over time, as the longshore drift carries more materials than the amount that is washed away

Wave refraction may cause the free end of the spit to curve to form a recurve or hooked spit