Coastal Zone Flashcards
What is a coast?
A coast is the boundary or interface between land and the sea.
What is a wave?
A wave is a long body of water, curling into an arch form and breaking on the shore.
How do waves form?
As wind passes over the surface, via friction and pressure, energy is transferred to the topmost layers of the water. These forces create a disturbance that are transported through the sea water and develop into waves. WAVES MOVE NOT THE WATER!
What determines the size or waves?
- Wind speed: greater with powerful storms.
- Wind duration: succession of storms in winter 2013-2014.
- Fetch: distance of open water over which the wind can blow (longer=more powerful).
Why do waves break?
- The sea becomes shallower.
- Friction against seabed slows the BOTTOM of wave.
- Top of wave is not slowed down by friction.
- Close to the shore the wave becomes increasingly elliptical (curved).
- Top of wave is mover much faster than the bottom causing the wave to break.
- Water rushes up beach (swash).
- Water returns down the beach due to gravity (backwash).
What are the properties of constructive waves?
-Lower, limited energy.
-Small height, flat (1m)
-Well spaced apart
-Strong swash (pushes material UP beach).
-Weak backwash
-Gentle slope.
-low frequency
The beach is built up as a result.
What are the properties of destructive waves?
-Higher energy
-Large height and steeper (3-4m)
-Close together (usually interfere)
-Weak swash
-Strong backwash (removes materials)
-Steep slope
-high frequency
The beach is destroyed as a result.
What is mass movement?
The downhill movement of material under the influence of gravity
What is slide?
Blocks of consolidated rock/earth slide downhill along a straight plane e.g. landslide
What is slump?
Slumping of saturated soil and weak rock on a curved surface e.g. rotational slip.
What is rockfall? (MM)
When fragments of rock ofter breakaway from the cliff face, often due to freeze thaw weathering.
What is landslide? (MM)
When material blocks of earth slide downhill along a rupture surface.
What is mudflow? (MM)
The movement of earth that behaves more like liquid because of saturation. Can be very slow (a creep) or very rapid.
What is rotational slip/slump? (MM)
The slumping of unsaturated soil and weak rock e.g. clay along a curved surface. This can be caused by undercutting at the base of a slope.
What is mass movement affected by?
- Human activity
- Amount of precipitation (soil saturated with water).
- Geology (solid rock or loose earth)
- Antecedent (previous) weather conditions (hot, dry, freezing, wet etc.)
What is weathering?
The disintegration or decay of rock ins situ or close to the ground surface.
What are the different types of weathering?
- Physical/Mechanical: disintegration of rock without any chemical change. e.g. freeze thaw weathering.
- Chemical: The decomposition of rocks is caused by a chemical reaction within the rock. e.g. acid rain can dissolve certain ricks and minerals.
- Biological: Involves the actions of fauna or flora e.g. plant roots expanding cracks in rocks or rabbits burrowing into weak rocks such as sand stone.
Describe freeze thaw weathering
- Water permeates into the rock and collects in pores and cracks.
- When the temperature falls below freezing at night the water freezes to form ice it expands by approximately 9% causing pressure in the rock and so the crack enlarge.
- When temperature rises above zero degrees, the ice melts releasing pressure. (The water thaws and contracts).
- After repeated freezing and thawing, the cracks widen and the water can seep deeper into rock. Eventually fragments of rock will fall from the main body of rock as scree.
Where is freeze thaw weathering most common?
Common where temperatures fluctuate repeatedly above and below freezing point.
Freezing occurs mostly at night.
Mid latitude and lots of rain.
Describe chemical weathering
- Rainwater has CO2 dissolved in it, making weak carbonic acid.
- Carbonic acid reacts with rocks that contain calcium carbonate e.g. carboniferous limestone and so the rocks are dissolved by the rainwater.
What are different forms of erosion?
- Hydraulic Power: as the sheer power of waves smash onto a cliff, trapped air is blasted into holes and crash on the rock. Eventually through repetition, the rocks break apart. The explosive force of the trapped air operating in a crack is called cavitation.
- Abrasion: the ‘sand papering’ effect of rocks rubbing against the rock surface often causing it to become smoother.
- Attrition: rock fragments carried by the sea knock against on another causing them to become smaller and more rounded.
- Solution: weak carbonic acid in seawater causes some rocks e.g. chalk and limestone to be dissolved.
- Corrasion: fragments of rock are hurled by the sea at the cliff, the rocks act as erosive tools by scraping and gouging at the rock.
What is a concordant coastline?
Concordant coastlines have the same type of rock along the coastline.
What is a discordant coastline?
Discordant coastlines are coastlines where the geology alternates between bands of hard and soft rock.
How are headlands and bays formed?
- Headlands (steep sides) and bays (gentle slope) are formed where the geology alternates between hard and soft rock at right angles to the coast (discordant coastlines).
- The harder rock is more resistant to erosion and so forms headlands which protrude out to sea.
- In contrast the softer rock is less resistant to erosion and so the waves erode this area more rapidly, forming bays that are set back from the coast.
Describe the formation of a wave cut platform
- At the base of the cliff waves hit between the high and low tide levels, this leads to coastal erosion occurring such as abrasion and hydraulic action, undercutting the cliff and forming a wave cut notch.
- Over hundreds of years the overhanging cliff can no longer support itself and so collapses.
- The sea continues to attack the cliff causing more wave cut notches to be formed.
- After this process is repeated, the cliff line gradually retreats inland, leaving behind a gently sloping rocky surface at the foot of a cliff called a wave cut platform.
- As it is below sea level at high tide it is usually eroded through hydraulic action and abrasion, causing it to be smooth.
Describe the formation of caves, stacks and stumps
- Headlands made of resistant rock may have weakness in them such as cracks which are vulnerable to erosion by hydraulic action and abrasion.
- Overtime this concentrated erosion (hydraulic action n and abrasion) creates a hollowed out feature in the cliff called a cave.
- Two back to back caves may deepen further breaking through the headland due to erosion forming an arch.
- Further erosion at base and weathering processes on its roof cause the arch enlarge and eventually they cause the arch to collapse as it is unstable.
- This leaves an isolated pinnacle of rock sticking out from the sea called a stack.
- The stack is further eroded by the waves leaving behind a stump which is only visible at low tide and covered by water at high tide.
What are the different types of coastal transportation?
- Traction: when heavy or large particles are carried along the seabed.
- Suspension: when lighter particles are carried within the water.
- Saltation: a ‘hopping’ or ‘bouncing’ of particles or pebbles (too heavy to be suspended) along the sea bed by the force of water.
- Solution: the transportation of dissolved chemicals.
What is longshore drift?
The transport of sediment along a stretch of coastline, caused by the waves approaching the beach at the same angle as the prevailing wind.