Coastal areas section 1 Flashcards
Describe wave motion towards shore
- 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
How To measure wavelength
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
Factors determining wave energy
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
Spilling breakers
characteristics (2)
Occur on beaches with gentle slopes
Break far from the shore
Plunging breakers characteristics (4)
Happen on beaches where the slope is moderately steep
Normally curls over, forming a tunnel until the wave breaks
Exerts considerable force
Surfer waves
Surging breakers characteristics (4)
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
Constructive wave characteristics
Gradient Energy environment Wave Height Wave length Wave frequency Swash comparison to backwash breakers type Where it occurs Coastal process
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
Why constructive waves have a stronger swash than backwash
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
Destructive wave characteristics
Gradient Energy environment Wave Height Wave length Wave frequency Swash comparison to backwash breakers type Where it occurs Coastal process
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
Describe wave refraction (4) and explain what happens when it converge/diverge on headlands and bays (4)
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
Where are headlands formed (4)
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
What happens at headlands
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
What happnes at bays
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
What does wave erosion refer to
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
Hydraulic action (C3E1)
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
Abrasion (c3e1)
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
Attrition (C+E)
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
Solution (C2E1)
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
Formation of a notch, cliff and shore platform (4)
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
Chartacteristicsof spit (2)
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
Formation of tombolo (1)
Tombolo is a beach that extends outwards to join an offshore island
Formation of bar
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
Essential conditions for spits / tombolos to develop (6)
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
Formation of sand dunes (4)
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
Formation of spit (8)
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
