Coastal Landscapes- waves, landforms, trasnport Flashcards
How are waves created
through friction between wind and water surface
-transfers energy from win into water- generating ripples which grow into waves
What is wavelength
horizontal distance from crest to crest
What is wave frequency
number of waves [passing a particular point over given period of time
Name 4 factors affecting wave size
- wind strength
- duration wind blows
- water depth
- wave fetch
Describe the 4 steps that occur when waves approach the coast
- water becomes shallower- circular orbit of water particles change to elliptical shape
- wavelength, velocity decrease, wave height increases
- force pushes wave higher before spilling and breaking on shore
- water rushes up beach as swash and flows back as backwash
Describe constructive waves
- low energy waves
- low wave height
- long wave length
- low wave frequency
-strong swash, weak backwash - strong swash pushes sediment up beach, depositing it as a (berm/ridge of sediment) at top of beach
-depositional
Describe destructive waves
- strong backwash, weak swash
-high wave height
-short wavelength
-high frquency
-erosional
-strong backwash- erodes
beach material and carries it offshore, creating offshore ridge
What is beach morphology
shape of the beach- width, slope, features, such as berms, ridges and runnels. It also includes the type of sediment found at different locations
What is a beach sediment profile
pattern of distribution of different size/ shaped deposited material
How does constructive waves alter beach morphology and sediment profile
- cause movement of sediment up beach- steeping beach profile
- produce berms (ridges of material) at point where swash reaches high tide
- leads to sorting of material- heavier shingle at back of beach, sand closer to sea
How does destructive waves alter beach morphology and sediment profile
- berms eroded by plunging waves, high-energy swash
- strong backwash transports sediment offshore
-
In which seasons are constructive waves dominant
-summer
In which seasons are destructive waves dominant
-winter
Explain daily variations in terms of contructive and destructive waves
-destructive waves change to constructive ones as the wind drops
What are the four different types of wave type that influences beach morphology
- Hydraulic Action
- Corrosion
- Abrasion
- Attrition
How does wave type and wave size influence erosion
- most erosion occurs during winter- when destructive waves are largest and powerful
- hydraulic action, abrasion, powerfully attack differences in rock resistance and weaknesses
- faster when wind is blowing directly onshore
- fastest when tide is high
How does lithology influence erosion
- any rock with weaknesses (joints, faults, bedding planes)
- result in formation of landscapes
- bands of more resistant rock between weaker joints and cracks erode slower
- fastest when rocks forming coastline are weaker
What is hydraulic action
Waves crash against rocks and compress air in the cracks, adding pressure. Repeated compression widens the cracks and causes rocks to shatter
What is corrosion
Water dissolves minerals in the rocks (particularly limestone-> carbonate rock) and washes it away
What is abrasion
Sediment picked up by breaking waves is thrown against the cliff face
The sediment acts like a tool on the cliff – chiselling away at the surface and gradually wearing it down
What is attrition
Eroded particles in the water collide with each other and break into smaller fragments
Name 5 erosional landforms
- blowhole
- retreating cliffs
- cave-arch-stack-stump seqeunce
- wave-cut notch
- wave-cut platform
What is a wave-cut notch
curved indentation (1-2m high) extending along base of cliff
-forms between high tide and low tide -> destructive waves
What is a wave-cut platform
flat rock surface exposed at low tide extending out to sea from base of cliff
How does a wave-cut platform form
- hydraulic action, abrasion at high and low tide mark form wave-cut notch
- notch deepens by further erosion- overlying material collapses (mass movement)
- process repeats, cliff retreats
- rock below low tide level is submerged
What are cliffs and how are they formed
steep slopes that are usually unvegetated
- hydraulic action, abrasion form wave-cut notch
- notch deepens, overlying rock collapses by mass movement due to gravity
- exposed face forms a cliff
How do cave, arches, stacks and stumps form
- rocks have joints, faults, bedding planes
- eroded more rapidly, hydraulic action, abrasion deepens and widens weak point- forming cave
- if 2 caves on either side of headland join up- single cave is eroded- forming arch
- top of arch collapses- leaving isolated pillar- stack
- stack is eroded by sea forming stump
What are the four different processes of sediment transport
Traction: Sediment rolls along, pushed by waves and currents
Saltation: Sediment bounces along, either due to the force of water or wind
Suspension: Sediment is carried in water columns
Solution: Dissolved material is carried in the water as a solution
Name 3 factors that affect sediment transportation
- angle of wave attack
- tides
- currents
- longshore drift
What is longshore drift
movement of sand and shingle along the coast
How does longshore drift affect sediment transportation
- swash transports sediment up beach at angle due to prevailing winds
- backwash transports sediment back down beach 90 degrees to coastline
- sediment particles come to rest along from starting point- lateral movement
- particle move in zig-zag fashion along beach with incoming wave
What depositional landforms are formed as a result of sediment transport deposition
- Beaches
- Spits
- Bars
- Barrier beaches
- Tombolo
- Cuspate Foreland
-Sand dunes
What is a spit
-long, narrow feature made of sand and shingle which extends from land into sea
When do spits form
- sand/ shingle moved along coast by longshore drift
- builds up when coastline chages direction- forming a spit
How are beaches formed
-wave refraction creates low-energy environment which leads to deposition
What is a recurved spit
spit which end is curved landwards- into bay
How are beaches formed
produced by material deposited by constructive waves
-swash has strength to carry material up beach, backwash transports some material back down beach, leaving it deposited
What are barrier beaches
when spit extends across a bay to join 2 headlands
-they trap water behind them forming lagoons
What are tombolos
a beach that has formed between a small island and the mainland
When does deposition occur
when waves no longer have sufficient energy to transport material
-material becomes too heavy
What are cuspate forelands
triangular shaped headlands that extends out from the main coastline
How does current influence sediment transportation
current is the flow of water in a particular direction- can transport sediment in nearshore, offshore zones
How do tides influence sediment transportation
create tidal currents in nearshore, offshore zones which transport sediemnt
Name one reason why depositional landforms are vulnerable to change
- made of unconsolidated material -> during storms -> sediment can be eroded -> transported elsewhere
- dynamic (lose material transported by waves, tides, currents, wind)
What can help stabilise depositional landforms
vegetation- as a result of plant succession
definition of plant succession
changing structure of a plant community over time as an area of initially bare sediment is colonised by plants
How does vegetation stabilise sediment
- roots of plants bind sediment particles together- harder to erode
- when submerged- plants growing in sediment provide protective layer- surface of sediment not exposed
- friction with vegetation slows wind speed- protects sediment from wind erosion
What effects the size of the wave
-Strength of the wind
duration the wind blows for
water depth
wave fetch
What is a sediment cell
a linked system of sources, transfers and sinks of sediment along section of coastline
What are the three types of coastal vegetation that can protect a coastline from erosion
- Coastal sand dunes
- Coastal salt marshes, found in many river estuaries
- Coastal mangrove swamps
What are Halophytes
Plants that can tolerate salt water, either around their roots, being submerged at high tide or salt spray from sea
What are Xerophytes
Plants that can tolerate very dry conditions (coastal sand dunes) -where sandy soil retains very little water due to drainage
What are salt marshes
areas of flat, silty sediments that accumulate around estuaries/ lagoons
Why does a recurved end occur to a spit
Wave refraction and a second dominant wind force material to move in a different direction
What are the three different types of weathering
mechanical
chemical
biological
Describe two types of Mechanical weathering
Freeze Thaw- occurs when water enters crack/ joint in rock
- water freezes and expands 10% exerting a force within cracks, widening and loosening rocks.
- broken rocks are used as tools in marine erosion
Salt Crystallisation- salt water evaporates- leaves salt crystals behind- these grow, cause stresses in rock- cause it to break
Wetting and drying- rocks in clay expand when wet, contract as they dry- causes them to crack and break
Describe the three different types of Chemical weathering
Carbonation- rain water mixed with co2 forms weak carbonic acid, mixes with calcium carbonate (in limestone)- forms calcium bicarbonate
-rock disappears as new minerals dissolve in solution
Hydrolysis- breakdown of minerals to form new clay minerals, due to effect of water and dissolved CO2
Oxidation- addition of oxygen to minerals, produces iron oxides and increases volume contributing to mechanical breakdown
Describe the two different types of Biological weathering
Plant roots
Trees and plant roots growing in cracks and fissures forcing rocks apart
Rock boring on vegetated cliff tops that can contribute to rockfalls
Name the 2 ways deposition can occur
- gravity- when energy of transporting water becomes too low to move sediment- large sediment is deposited, then smaller sediment
- flocculation- when small particles are so small they remain in water- clump together- large enough to sink
What is biological weathering
breakdown or rock in situ by living/ once-living organisms
What is mass movement
downslope movement of material under force of gravity
How does the type of mass movement depend upon lithology
- unconsolidated material- leads to slumping
- consolidated rock- sliding
Name the 3 distinctive landforms mass movement creates
- rotational scars
- talus scree slopes
- terraced cliff profiles
What are human changes that can cause beach profiles to change?
construction of dams blocking sediment supply
global warming creating more storms
coastal management intefering with sediment supply
What is a blowhole
co,bination of 2 features;
-pothole on top of cliff -> created by chemical weathering
-cave formed by marine erosion
-as cave erodes deeper, pothole deepens -> meet -> gap is created for waves to enter travel in and up cliff
What are the 4 processes of sediment transport, and the type of sediment they transport?
traction - pebbles, boulders
saltation - sand sized particles
suspension - silt and clay particles
solution - chemical compounds in solution
What is a swash aligned coast?
Where wave crests approach parallel to the coast, so -> limited longshore drift
What is a drift aligned coast?
where wave crests approach at significant angle -> longshore drift causes sediment to travel far up beach
Name 2 factors which effect transportation of sediment
-swash-aligned - wave crests paralell to coast -> limited LSD
-drift-aligned - wave crests significant angle -> LSD -> sediment far up beach
Desposition is a gradual and continous process
-name 2 forms of desposition
-gravity settling -> when waves energy = v low -> heavy rocks, boulders deposited
-flocculation -> clay particles clump together due to chemical attraction and then sink -> ^ density
How do sand dunes form
when prevailing winds blow sediment to back of beach
