coasts Flashcards
wave length
horizontal distance between crests
crest
top of a wave
trough
bottom of a wave
wave height
the vertical distance to the crest
wave frequency
number of waves breaking per minute
fetch
distance the wave has travelled uniturrupted over open water
swash
the water moving up the beach by energy from the wind
backwash
the wave moving back down the beach under the influence of gravity
characteristics of a constructive wave
long wave length
low frequency
low wave (under 1m)
wave front gently sloping
gains little height then breaks and slpis onto the beach
low energy
strong swash
weak backwash
characteristics of a destructive wave
high energy
steep wave front
wave height over 1m
gains height
restricted swash
strong backwash
plunges onto the beach so doesnt travel far
reasons why some waves are stronger than others
-how long the wind has been blowing (more energy transfered)
-speed of the wind, strong winds result in stronger waves as more energy is tranferred
-fetch as the longer the fetch the larger the possibility of large waves
what is weathering
breaking down of rocks by the action of the weather, can be physical or chemical
what is mechanical weathering
disintergration of rocks and is associated with extremes of temp and water. the rock is broken down without its chemical composition changing
what are the 2 main types of mechanical weathering
freeze thaw and salt weathering
what is freeze thaw
occours when it rains in places where it is very cold. When it rains in the day water gathers in cracks in the cliff. At night when temps drop the water freezes and expands by 9%. This freezing and thawing repeats making cracks bigger putting pressure on surrouding rocks. this causes rocks to break off from the cliff
what is salt weathering
when salt spray gets into cracks in cliffs, the water evaporates leaving behind salt which crystalises putting pressure on the surrounding rocks and weathering the structure
what is chemical weathering
Happens when a chemical reaction causes the rock to decompose/break up
rainwater mixes with carbon dioxide in the air the rain water then becomes a weak carbonic acid this acid then attacks the alkaline rocks especially chalk on limestone. The Rock is slowly dissolved by the acid and weakened over time
How does Mass movement happen
Mass movement is the downslope movement of rock soil or mud under the influence of gravity heavy rainfall usually triggers this
What is Rock fall
Fragments of rock breakaway from the cliff face due to weathering EG freeze thaw
what is slide (mass movement)
blocks of rock slide downhill
what is a slump (mass movement)
saturated soil slumped along a curved surface
What is DEPOSITion
Deposition is where the waves break and leave behind material they were transporting deposition results in more sediments staying on the beach then is taken away by the backwash
What is erosion
Erosion is the wearing wave rocks and on the coastline by the action of water or the wind this material is then transported
Why does deposition happen
Coastal deposition takes place in areas where the flow of water slows down waves loose energy and are no longer able to transport material
Where does deposition happen
Deposition happens along sheltered bays and where water is protected by Headlands spits or bars as sediment can no long be carried or moved this explains why beaches are found in Bays and mud flats and salt washes are often found in sheltered estuaries behind spits
What is traction
The largest material boulders are rolled along the Ocean Floor
What is saltation
(transportation)
Pebbles or Stones bounce Along The Ocean Floor
What is suspension
Suspension is smaller particles (sand) are held in the flow of water
what is long shore drift
long short drift is a process in which transported material is moved across the coastline. the direction is determined by the prevailing wind
Process of longshore drift
The prevailing wind blows waves into the coast at an angle. The swash bring sediment up the beach at the same angle as the prevailing wind. the backwash goes down the beach at a right angle due to gravity. this process continues moving sediment along the beach in a zigzag motion
What is a concordant coastline
A concordant coastline occurs when layers of different rock types are folded into ridges running parallel to the coast the outer Hard Rock provides a protective barrier to the soft rocks sometimes the hard rock is punctured allowing sea behind creating coves
What is a discordant coastline
A discordant coastline occurs where bands of different Rock types run perpendicular to the coast the differing resistance to erosion leads the formation of headlines and bays these can only form at discordant coastlines where you have alternating layers of soft and hard rock
What is wave refraction
The Wave Crest is in deep water but it doesn’t reflect the shape of the Land as the Wave Crest approaches a discordant coastline it takes shape of the coastline the part of the Wave Crest due to break on the Headland experiences shallow water and frictional drag slowing down the lower part of the wave on the side of the headline the fast parts of the wave bend to water the head and keeping the line of the crest intact and concentrating more energy on the Headland increasing the rate of erosion
What is a wavecut platform
A wave Cut platform is a wide gently sloping surface found a bit Cliff base and extends into the sea it is often in places where Cliffs are made from more resistant rocks
Explain the creation of a wave cut platform
A version is concentrated between the higher and low tide level continued erosion causes the rocks to break away and collect the base of the cliff this material is then removed by destructive waves the cliff now has a wave cut notch. the section of the cliff the notches is unsupported eventually notch is enlarge until it breaks away the rock on top and falls onto the beach creating a new cliff.
sandy beach characteristics
constructive waves
Shallow or flat
long beaches
sometimes has sand dunes
Where do sandy beaches form
In sheltered bays where swash is stronger than backwash
Characteristics of pebble beaches
Steep
destructive waves
short beaches
Where do pebble beaches form
On an exposed beach with a large fetch stronger backwash and Swash
Beach profile
Shows the gradient of a beach from the back of the beach to the sea a sandy beach generally has a gently profile compared to a pebble beach
What is the near shore of a beach
The breaker zone where waves break
What is the backshore of a beach
An area that is not usually affected by waves so the sun is normally dry
what is the fore shore of a beach
The intertidal zone repeatedly covered then uncovered by changing tides
What is the offshore of a beach
The part of a beach that is fairly far out to see so the waves do not break
What is the berm of a beach
A terrace on the beach that is formed in the back Shore formed by constructive waves transporting material onto the beach
What is an embryo Dune
A new formed sand dune close to the sea these dunes form around debris on the beach and sand dunes are transported by wind
what is a fore dune
Jeans that have become more stabilised our slightly taller than embryo dunes marram grass is a dominant species
What is a yellow Dune
Jeans with high organic matter due to other plants decomposing meaning plants such as lichens and thistles may start to colonize
What is grey dune
These dunes are described as Gray due to the litchens that grow there as well as the organic matter mixed with sand
What is dune Slack
A trough or a low point in a line of dunes formed as sediment is removed from the Leeward base of one Dune and burn up the windward side of the next the slack may be eroded and reached the water table it’s the access to freshwater allows ponds with Reeds and other water-loving plants to form
What is a mature Dune
The oldest and most established tunes with much less high conditions as it is more sheltered and greater access to Freshwater small trees may even grow her
What are the conditions needed for a sand Dune to form
a large flat beach
A large supply of sand
time for the Sand dry so a large title range needed
a prevailing onshore wind
What is suspension( in the transportation of sand)
When the sand is picked up and carried by the wind only 1% of sand is moved by this process
What is creep( in the transportation of sand)
When sand grains collide with each other and push each other along 4% of transportation is by this process
What is saltation( in the transportation of sand)
When grains of sand bounced on the beach as they have picked up and dropped by the wind in 95% of sand is moved this way
How are spits formed
(have to explain & known longshore drift)
Spitz operated by deposition they are formed when the prevailing wind blows an angle to the coastline resulting in longshore drift and the coastline changes Direction example of a spit is spurn heal
Formation of a bar or Tom bolo
(have to explain & known longshore drift and formation of a spit)
When is spit grows across a bay and joins two headlines together this forms a bar ,when a spit connects an island to a mainland it’s a tombolo
What is hard engineering
Involved using expensive artificial structures to try and control natural processes
What is a seawall
Concrete structures please at the further cliff or the top of the beach Curve to reflect the energy of a wave
What are groynes
Wooden or rock features that built angles to the coast and our place about 50 meters apart they stop sediment being transported by longshore drift
What is rock armour or rip rap
Large boulders place at the foot of a cliff which absorb the energy of a wave as water enters gaps between the builders pressure is released and it reduces the waves energy
What are gabions
Mesh cages for with rocks and pebbles they are placed at the back of sandy beaches to make a wall like structure
What is soft engineering
Doesn’t involve building artificial structures but takes a more sustainable and natural approach to managing coasts
What is beach nourishment
Broad term for the replacement of a lost beach sediment
what is Beach repro filing
The artificial reshaping of a beach using existing beach material after winter storms buddhas is move shingle back up the beach
What is dune regeneration
The artificial creation of sand dunes or restoration of existing ones sand dunes acts as a physical barrier between the sea and the land they absorb wave energy and water
What is managed retreat
This is Libera and controlled process of allowancy to flood low line coastal areas
