Coastal Zone Processes and Forms Flashcards
What percentage of the world’s population live within 2km of the coastline?
50%
What does the coastal change exhibit change over?
A range of timescales
What does the coastal zone adjust to?
Wave, tide and current processes
What is the coastal zone an important buffer between?
The marine and terrestrial environments
What 4 things does the coastal zone act as?
Important ecological reserve
Economic resource
Communication corridor
Recreational playground
What are the 4 areas of the coastal zone?
Coastal plain
Shore
Nearshore
Offshore
What is the shore composed of?
Foreshore and backshore
Where do waves break?
In the surf zone
Where does swash and backwash occur?
The shoreline
What are sea waves produced by?
Localised storm activity at sea
How do swell waves form?
Once the waves have left the generation area, they lose height and energy to become swell waves
What is the wave form?
Sinusoidal form
What are 6 definable components of waves?
Wave crest Trough Height Steepness Frequency Period
What does wave height increase with?
Wind speed, duration and fetch distance
What was the largest wave ever recorded?
34m in february 1933 in the Pacific
What type of wave moves fast?
Long waves
What type of wave dissipates a lot of its energy along its journey?
Short waves
What type of wave moves slow?
Short waves
What type of wave doesn’t lose much energy?
Long waves
What waves do coasts facing the open ocean experience?
Long waves that have overwhelmed short waves
What waves are deflected by the Coriolis effect?
Deep water waves
Why can small ripples evolve into full sea waves?
Due to wind duration and frictional drag on the sea surface
What can a ripple increase?
Sea surface area
What is a result of increasing the sea surface area?
Air mass has more frictional drag which increases wave amplitude
What pulls up the ascending limb?
The push of the air mass
What pulls down the descending limb?
The force of gravity
What is the height of the wave proportional to?
The height of the wave is DIRECTLY proportional to the strength and duration of the wind passing over the surface
Why do wave fields occur?
Waves produced at different times and places and vary in magnitude, direction and speed meet together
What happens when two waves meet to form a wave field?
They become superimposed on each other and produce complex wave fields
What are the patterns of wave fields?
Cyclic-surf-beat
What happens with waves on short fetch coastlines?
They arrive at the same time as choppy conditions
Why do waves on short fetch coastlines arrive at the same time as choppy conditions?
They have insufficient time to separate
What happens to the waves on long fetch coastlines?
Long waves dominate and surf beat develops
What does a wave perturb when it approaches the coastline?
A wave perturbs the water depth equal to 1/2 wavelength to the wave base
Where does schoaling occur?
When the wave depth is greater than the water depth
What happens to waves in shallow water?
Frictional drag of bed causes the wave to slow
Wave length decreases but wave height increases
Steepens until unstable and breaks
What is the critical ratio of water depth to wave height when waves are in shallow water?
0.6=1.2
What type of wave travels further coastward before breaking?
Low waves travel further coastward before breaking
What does shoaling cause?
The orbital wave motion to become distorted
Why is the angle of the shore important?
Steep- waves break close to the shoreline
Flat- waves break further offshore
What are the 4 things waves can do when they reach the coastline?
Spill, plunge, surge or collapse
What 3 things does the interaction of the wave with near shore topography cause?
Refraction
Reflection
Diffraction
What are tides?
Waves generated by the gravitational pull of astronomical bodies
What does the gravitational force of the moon cause?
Reduction in the Earth’s centrifugal force which affects the oceanic surface mass
What are the two main features of spring tides?
Greater magnitude tides during new and full moon
Sun and moon pull along the same vector
What are the two main features of neap tides?
Less magnitude tides during half moon phases
Sun and moon pull in opposite direction
Which type of tide (spring or neap) has stronger tides?
Spring tides are stronger
Which type of tide (spring or neap) has a higher tidal range?
Spring
What is the rate of the longshore currents?
0.1-0.2ms-1 to 1ms-1 if wind direction is along shore
Explain longshore currents
Water moves along the beach and gets trapped between breaking waves and beach slope
Why are rip currents dangerous?
They develop a strong circulation cell
How are rip currents formed?
Water forced up the beach forces its way back down the slope against breaking waves along the line of least resilience
What are tidal currents due to?
The rise and fall of the tide
What are swash and backwash mechanisms for?
Movement of sediment up and down the beach
What is longshore drift?
Sediment movement along the beach in swash and backwash at an angle.
What is net erosion?
Longshore drift with no sediment supply from the coast
What is a pocket beach?
A crescent shaped beach
How do pocket beaches form?
Sediment from eroding cliffs is transported by littoral drift along the sides of the bay. This then converges on the head of the bay
What is erosion a function of?
Wave environment, local geology and coastal morphology
List 7 marine processes
Wave quarrying Abrasion Wetting-drying Salt crystallisation Thermal expansion and contraction Biological activity
Give 3 examples of sub aerial processes
Landslides
Rotational slumps
Mudflows
What is coastal retreat?
The cyclical removal of fallen sediment from a cliff base
What are developed as a result of coastal retreat? (5)
Wave cut notches, caves, arches, stacks and blowholes
What complex feedback occurs at coasts?
Between the cliff erosion, platform width and wave energy potential
What are 3 types of cliff and shore platform morphology?
Sloping shore platform
Horizontal shore platform
Plunging cliff
What is an example of a depositional landform?
A beach
What is a beach?
Accumulation of unconsolidated material
Why is dynamic equilibrium maintained at beaches?
Sediment is highly mobile
What is a beach profile a function of?
Coastal processes and sediment type
What are three topographical features found on beach profiles?
Cusps, berms and ripples
What can often be found above high tide?
A coastal dune system
Why are there curved features on beach planforms?
Due to refraction
What 5 things can be found on a beach planform?
Spits Barrier islands Barrier beaches Tombolos Lagoons
What are the 3 models for barrier beach formation?
Emerged-transgressive model
Submerged-transgressive model
Emerged-standstill model
Explain the emerged-transgressive model
Offshore bars formed during last glacial low SL period
Bars develop vertically and sediment accumulates as sea level rises
Explain the submerged-transgressive model
Coastal dunes during the lower sea levels
Become isolation from mainland upon submergence
Explain the emerged-standstill model
Barrier islands formed since post-glacial sea level stabilised 4000 years ago
What evidence is against the emerged standstill model
Many barrier island deposits are older than 4000 years old
What are estuaries?
Coastal embayments from which rivers flow
What can shift the estuaries in tide dominated coasts?
Tidal currents shift inlet channels
Where do estuaries receive sediment from?
The sea and river
When do estuaries form and what is this opposite to?
They form when net sediment movement is landwards and this is opposite to deltas
What are the 3 subdivided spatial facets of tide dominated estuaries?
Upper estuary
Lower estuary
Middle estuary
What dominates the upper estuary in tide dominated coastlines?
Fluvial
What dominates the middle estuary in tide dominated coastlines?
Well mixed
What dominates the lower estuary in tide dominated coastlines?
Tidal
What are the two types of estuary?
Tide dominated
Wave dominated
What is salt-fresh water mixing a result of in estuaries?
Diffusion and advection
What happens to the form of estuaries overtime?
They become more and more similar
On what type of coast can deltas be found?
River dominated coasts
Where do deltas form?
At the mouth of sediment rich fluvial channels
What are the 3 main groups of deltas?
Cuspate
Elongate
Estuarine
What do some deltas resemble?
A bird’s foot with branching distributaries carrying river water and sediment to the ocean
What are short term sea level changes due to?
Tidal
Meteorological
What are longer term changes in sea level due to?
Isostacy and eustacy
Give 3 types of evidence for sea level change
Erosional and depositional landforms
Biological indicators
Archaeological remains and historical records
Give two examples of erosional and depostional landforms that are evidence of sea level change
Tidal flats and wave cut notches
Give an example of a biological indicator of sea level change
Fossils
What does falling sea level cause?
Abandonment of coastal features
What does rising sea level cause? (3)
Drowning of coastal features
Migration of mobile features
Increased erosion
What is the orbit of a wave?
Circular movement of water
What are waves produced by?
Wind
What are waves a source of?
Energy
What type of wave lengths are associated with tsunamis?
Long wave lengths
When do waves start to show?
When the wave base hits the shore
How does the wave shape change when the wave base hits the shore?
Changes from orbital to elliptical
What type of wave fronts do steeper beaches tend to have?
Steeper beaches tend to have smaller wave fronts
What two cycles are tides dominated by?
Lunar and solar
