Coasts: Retrieval Flashcards
, bnkml/,. n What is Weathering?
Weathering is when rocks are attacked by the weather
Basically “The decomposition of a rock”
What is mechanical weathering?
Mechanical weathering is where the rock is physically forced apart
Describe the process of Freeze-thaw weathering (Frost shattering)
1)Water collects in a crack of a rock.
2)The water freezes and expands (by around 9%) - forcing the crack to widen
3) The expansion and pressure causes the crack to split
–Repeated Freeze-thaw can cause the rock to break up
(Temperatures need to be below freezing)
Describe the characteristics of rock that has recently been through freeze-thaw
Recently weathered rock can be seen at the foot of a chalk or limestone cliff
Is easily identified due to it being angular
What is salt weathering?
-When the salt spray from the sea gets into a crack in a rock.
-The salt spray may evaporate + crystallize, placing pressure on the surrounding rock and weakening the overall rocks structure.
What is chemical weathering?
-Breakdown of rock through its changing chemical composition
Describe carbonation weathering
-When slightly acidic (carbonic) rain or sea water comes into contact with sedimentary rock,, such as limestone or chalk, it causes it to dissolve.
-A chemical reaction occurs between the acidic water and calcium carbonate = calcium bicarbonate ——- this is soluble and carried away in solution.
-Carbonation weathering occurs in warm, wet solutions
What is MASS MOVEMENT?
-Mass Movement is the downhill movement of cliff material under the influence of gravity.
4 Types of Mass Movement
-Rockfall. (Bits of rock fall off the cliff face, usually due to freeze-thaw weathering.)
-Mudflow. (Saturated soil (soil filled with water) flows down a slope.)
-Landslide. (Large blocks of rock slide downhill.)
-Rotational slip. (Saturated soil slumps down a curved surface.)
Large blocks of rock sliding downhill is what type of mass movement?
Landslide
What type of mass movement involves fragments of rock breaking away from the cliff face due to freeze-thaw weathering
Rockfall
What type of mass movement involves saturated soil and weak rock flows down a slope, typically where cliffs are made up of boulder clay?
Mudslide
What is Coastal Erosion?
Coastal Erosion is the wearing away of the land bythe sea
Main Processes of Coastal Erosion?
Corrasion, Abrasion, Hydraulic Action, attrition and corrosion/solution
What is Abrasion?
Abrasion occurs when the pebbles carried by the waves grind along a rock platform much like sandpaper. Over time the rock becomes smooth.
What is Attrition?
Arritrition is when waves cause rocks and pebbles to bump into each other and break up
What is Hydraulic Action?
Hydraulic Action is the sheer power of the waves as they smash against the cliff. Air becomes trapped in the cracks in the rock and causes the rock to break apart
What is Solution?
Solution is where certain type of cliffs (such as limestone and chalk) erode due to the weak acids in the sea
What is Coastal Transportation?
The movement of sediment and beach material through wave action
4 Main Processes of Coastal Transportation
-Solution
-Suspension
-Saltation
-Traction
What is Traction?
Traction is when large pebbles and boulders are rolled among the sea floor
What is Saltation?
Saltation is the coastal erosion process of having beach material be bounced along the seafloor
What is suspension?
Suspension is when beach material is suspended and carried by the waves
What is Solution?
Solution is where material is dissolved and carried by the water
What is Longshore Drift?
Longshore Drift is the movement of material down a coastline due to the angled approach of the waves
Describe Longshore Drift
-Longshore Drift occurs when waves approach the beach at an angle.
-The swash (waves moving up the beach) carries materials up and along the beach.
-The backwash (waves moving back down the beach)
carries material back down the beach at right angles.
-This process slowly moves material along the beach + provides a link between erosion and deposition
-Material transported thru suspension, traction, solution and saltation.
What is coastal Deposition?
-Coastal transportation involves material being transported by the sea being deposited or dropped
Why does Coastal Deposition occur?
-Wave energy reduces resulting in material being deposited
3 conditions that may lead to
3 conditions that may lead to Coastal Deposition occuring:
-Waves enter an area of shallow water
-Waves enter a sheltered area e.g cove or bay
-A river or estuary flows into the sea reducing wave energy
What is a headland?
A headland is a cliff that sticks out into the sea and is surrounded by water on 3 sides
What is a bay?
A bay is an inlet of the sea where the land curves inwards
Which type of coastline do headlands + bays form from?
Discordant bays where bands of soft and hard rock are on a right angle to the coastline
Due to the type of rock, the rock erosion occurs at different rates
Whats a discordant coastline?
-A discordant coastline is where the geology alternates between bands of soft and hard rock
What is a concordant coastline?
-A concordant coastline is where the same rock type runs along the length of the coast
-These coastlines tend to have less bays and headlands
Explain Formation of Headlands + Bays
–Bands of soft rock (such as sand and clay) erode more quickly than those of more resistant rock such as chalk.
-This leaves a section of land jutting out into the sea called a HEADLAND.
- The areas where the soft rock has eroded away,next to the headland, are called bays
Why are sandy beaches likely to form in bays?
-Sandy beaches are often found in bays where waves lose energy, and their capacity to transport material decreases = more material being deposited
What is a wave-cut platform?
A wave cut platform is a wide, gently sloping surface found at the base of the cliff and extends into the sea.
How is a Wave-cut platform formed?
-The sea attacks a weakness in the base of the cliff. E.g a Joint in the chalk
- A wave-cut notch is created by erosional processes such as hydraulic action and abrasion
-As the notch becomes bigger, the cliff becomes unstable and collapses as a result of gravity
- The Cliff retreats inland
-The material from the collapsed cliff is eroded and transported away, leaving a wave-cut platform
-This process REPEATS over time
How is a “Stump” formed?
1) Cracks in the base of the headland are enlarged through hydraulic action - the air becomes compressed, widening the cracks as it escapes
2)Cracks enlarge through weathering processes like salt crystallization
3) Cracks widen and a cave is formed through abrasion and hydraulic action
4)Cave increases in size as refracted waves concentrate their energy on the sides further enlarging the cave
5)Where two caves are aligned the waves may cut through to form an arch. Wave cut notches widen the arch
6)Over time the roof becomes weakened by freeze thaw or salt crystallization . The arch will collapse under its own weight forming a stack
7) Base of stack will be eroded through abrasion and hydraulic action.
8)Eventually, wave cut notches will form and the stack will collapse forming a stump
What case study location?
Old harry:
Stump and arch
3 landforms of coastal deposition:
Beaches, sand dunes, spits + bars
What is a beach?
The beach is the area between the lowest spring tide level and the point reached by the storm waves in the highest tides
Where do sandy beaches typically form?
A sandy beach is usually formed in a sheltered bay where low energy, constructive waves transport material onto the shore
Beach Profile:
-Dunes or storm beach
-Backshore
-Foreshore( covered and uncovered by the tide)
-Nearshore (breaking waves)
-Offshore (waves not breaking)
What are ridges and runnels?
Ridges = Areas of the beach that are raised
Runnels = Dips of water-filled troughs
What is a spit?
A spit is an extended stretch of beach material that sticks out to sea and is joined to the mainland at one end
How is a spit/spurn-head formed?
1) Longshore drift moves material along the coastline in the direction of the wind. Ongoing swash brings material onshore while backwash removes the material in a straight line, perpendicular to the coastline
2) This continues in a zig-zag movement along the coast
3) If the coast changes direction, material will continue to be deposited in the original direction in a shallow sea
4) This build up of material is called a spit
5) A spit needs constant supply of material to prevent being moved by the tides
6) Over time the spit grows + develops a hook if wind direction changes further out
7) Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form
What is a bar?
A bar is a ridge of sand or single that joins two headlands either side of a bay
How is a bar formed?
-A bar is created when there is a gap in the coastline with water in it. This could be a bay or a natural hollow in the coastland.
-Longshore drift occurs and carries material across the front of the bay
-Material is pushed onto the beaches at a 45 degree angle when the swash brings it back across the coastline. The backwash takes it back out towards the sea at a right angle to the coast.
-Throughout this process, material is constantly moved along the coastline
-The deposited material eventually joins up with the other side of the bay and a strip of deposited material blocks off the water in the bay. The newly formed area = a lagoon
What is an off shore bar?
An offshore bar is a raised area of seabed that is found offshore
How is an off-shore bar formed?
-Offshore bars form when sediment is transported on + off a beach
-Destructive waves remove sediment from the beach and form the offshore bar
What is a sand dune?
A sand dune is a small ridge or hill of sand found at the top of a beach, above the reach of the waves
How are sand dunes formed?
-Onshore winds (winds blowing inland from the sea) cause the formation of sand dunes at the back of a beach
-Sand is deposited by the wind around an object such as rock, forming embryo dunes.
-Over time, vegetation such as marram grass stabilize the sand dunes forming foredunes.
-As the vegetation around the foredunes decompose nutrients are released and soil beings to form
-A wider range of plants are then able to colonize the dunes
What is Hard Engineering?
Hard Engineering involves building artificial structures which try to control natural processes
