Coasts Flashcards
Are coasts an open or a closed system
Open system
Inputs
Material or energy moving into the system to the outside. Eg: Precipitation and wind
Output
Material or energy moving from the system to the outside. Eg: Ocean currents, rip tides, sediment transfer and evaporation
Energy
Power or driving force. Eg: Energy associated with flowing water, the effects of gravity on cliffs and moving air
Stores/Components
The individual elements or parts of a system. Eg: beach, sand dunes, nearshore sediment
Flows/transfers
The links between the components. Eg: Wind-blown sand, mass movement processes, longshore drift
Positive feedback
Where a flow/transfer leads to increase or growth. Eg: coastal management leading to an increase in erosion elsewhere
Negative feedback
Where a flow/transfer leads to a decrease or decline
Dynamic equilibrium
This represents a state of balance within a constantly changing system
Wave length
The difference between the two wave crests
Wave crest
The top of the wave
Wave trough
The bottom of the wave
What happens to a wave when it reaches the beach
It starts to create an elliptical wave orbit (the wave motion becomes more like an oval)
Features of a constructive wave (4)
-Low waves with a long wavelength
-Strong swash, weak backswash
-Builds the beach
-Associated with a gentle beach profile but will make the beach steeper over time
Features of a destructive wave (4)
-High waves with short wavelengths
-Weak swash, strong backwash
-Beach loss (destructive)
-Usually associated with a steeper beach profile but will flatten the beach over time
How can constructive and destructive waves be an example of a negative feedback loop?
Constructive waves make a flatter beach steeper, which creates more destructive waves which flatten the beach
Tides
Tides are changes in water levels of seas and oceans caused by the gravitational pull of the moon
Rip currents
Strong localised underwater currents that pull things back out to the sea when things are caught in them
Wave refraction
The distortion of wave fronts as they approach an indented shoreline. This causes wave energy to be concentrated on headlands and dissipated at bays
What are the sources of sediment for a sediment cell (6)
-Rivers
-Cliff erosion
-Longshore drift
-Wind (wind blown sediment)
-Glaciers
-Offshore (sediment being transferred from offshore by waves
Sediment cells
A stretch of coastline, usually bordered by two prominent headlands, where movement of sediment is more or less contained
Sediment budget
The losses and gains of sediment in a sediment cell
Fill in the blank: The sediment budget aims to achieve a state of __________________.
Dynamic equilibrium
Weathering
The breakdown or disintegration of rocks in situ (in place)
What are the three types of weathering
-Mechanical weathering
-Biological weathering
-Chemical weathering
What are the different types of mechanical weathering (3)
-Frost shattering (freeze-thaw)
-Salt crystallisation
-Wetting and drying
Frost shattering (freeze-thaw) weathering
When water enters a crack or joint in the rock and then freezes. This causes the water to expand by 10% which exerts pressure on the rock and forces the crack to widen.
Salt crystallisation
When salt water evaporates, it leaves salt crystals behind, which can grow over time and exert stress on the rock
Wetting and drying
Rocks rich in clay expand when they get wet and contract when they are dry, causing cracks to form
Biological weathering
The break down of rocks by organic activity
How can biological weathering occur (4)
-Thin plant roots grow into cracks in the rocks, and as the roots grow the cracks widen and break
-Water running through decaying vegetation becomes acidic, which leads to chemical weathering
-Birds and animals dig burrows into cliffs
-Marine organisms burrowing into rocks or secreting acid
Chemical weathering
A chemical reaction that allows for rocks to be easily eroded
Three types of chemical weathering
-Carbonation
-Oxidation
-Solution
Carbonation
Rainwater absorbs carbon dioxide from the air to form weak carbonic acid. This reacts with calcium carbonate in rocks (such as limestone and chalk) to form calcium bicarbonate which is easily disolved
Oxidation
The reaction of minerals with oxygen to form a rusty red powder leaving rocks more vulnerable to weathering
Solution
The dissolving of rock minerals
Mass movement
The downhill movement of material under the influence of gravity
What are the 5 types of mass movement
-Soil creep
-Mudflows
-Landslide
-Rockfall
-Landslip or slump
Soil creep
An extremely slow form of movement of individual soil particles down a hill. This usually happens as a response to wetting and freezing
Mudflows
Earth and mud flowing downhill, usually after heavy rainfall and over weak bedrocks such as clay
Landslide
A block of rock moving rapidly downhill, that remains largely intact
Rockfall
The sudden collapse or break away of individual rock fragments at a cliff face
landslip/slump
They are a curved plane of land where permeable rock lies of impermeable rock, causing the permeable rock on top to slip
Name the five types of coastal erosion
-Hydraulic action
-Abrasion
-Corrasion
-Solution
-Wave Quarrying
Hydraulic action
When wave traps and compresses air in cracks in the cliff face and then retreats, it causes the compressed air to expand
Wave quarrying
Waves scooping out materials such as gravel or sand, similar to a digger
Corrasion
When bits of sediment get hurled at a cliff by waves
Abrasion
When sediment is dragged up and down the shoreline, eroding and smoothing rocky surfaces
Solution
Weak acids in salt water dissolve
What are the 4 coastal transportation methods
-Traction
-Saltation
-Solution
-Suspension
Traction
The rolling of sediment along the sea bed
Saltation
Sediment is bounced along the sea bed
Suspension
Sediment is picked up and carried with the flow of the water
Solution
Sediment is dissolved in water
What type of rock is required for steep cliffs
Hard rock
What type of rock creates gentle cliffs
Softer rock
Coastal morphology
The underlying geology, rock type and physical composition of a coastline
What are the 6 characteristics that make up the coastal morphology
-Strata
-Bedding planes
-Joints
-Folds
-Faults
-Dips
Strata (coastal morphology)
Layers of rock
Bedding planes (coastal morphology)
Horizontal, natural breaks in the strata, caused by gaps in time during periods of rock formation
Joints (coastal morphology)
Vertical fractures caused either by contractions as sediments dry out, or by earth movements during uplift
Folds (coastal morphology)
Formed by pressure during tectonic activity, which makes rocks buckle and crumple
Faults (coastal morphology)
Formed when the stress or pressure to which a rock is subjected exceeds it’s internal strength. The faults then slip or move along fault planes
Dip (coastal morphology)
Refers to the angle at which rock strata lie
Geo
An inlet or gully or a narrow deep cleft in the face of a cliff
How do Geos form?
When there is a layer of soft rock that is surrounded by hard rock (on a discordant coastline) then a geo can be formed as the soft rock gets eroded away but the hard rock doesn’t
Discordant coastlines
When you have layers of hard rock and soft rock that are perpendicular to the coastline
Concordant coastlines
When you have layers of hard and soft rock that are parallel to coastline
What is a swash aligned beach
Low energy energy environments (because of wave refraction), where most of the beach is made up from sediment brought in by the waves
What is a drift aligned beach
Where the waves approach the beach at an angle. Longshore drift will move sediment along the beach often forming a spit
How is a spit formed
When longshore drift move sediment along a coastline and there is a sudden change in the coasts direction (The mouth of a river) then the sediment will extend out into the sea making a spit. The end of the spit will then begin to curve back towards the coast
Tombolo
A beach or ride of sand that has formed between a small island and the mainland
Offshore bars
Submerged ridges of sand or coarse sediment created by waves offshore from the coast. They absorb wave energy and reduce the impact of erosion on the coastline
Barrier beaches (bars)
When a beach or a spit extends across a bay to form two headlands it forms a barrier beach or a bar (Slapton Leigh)
What are the 5 stages of sand dunes
-Embryo
-Fore dunes
-Yellow dunes
-Grey dunes
-Dune slack
-Woodland (mature dunes)
Humus
Organic material that forms in soil when plant or animal matter decays
Explain the process of sand dune formation
Embryo dunes develop first as sand and shingle gets built up on a beach. Then the fore dunes are created, and held together with sea rocket and couch grass. Then as the plants die and the humus of the sand dunes increase, yellow dunes are formed and held together by marram grass. The dunes now start to darken and turn into grey dunes with low shrubs and brambles. Then dune slacks are formed where there is a depression that is close to the level of the sea, so water often fill up the hole. The behind it you have the mature dunes r woodland with gorse bushes and oak and pine trees.
What happens to the soil PH of sand dunes
Embryo - 8.5
Yellow dunes - 7.5
Grey dunes - 6.5
Woodlands (mature dunes) - 4.5
What happens to the % humus in sand dunes
Fore dunes - 1%
Yellow dunes - 2.5%
Grey dunes - 10%
Woodland (mature dunes) - 40%+
Saltmarshes
Areas of flat,silty sediment that accumulate around estuaries and lagoons
The three conditions for salt marshes
-In sheltered areas where deposition occurs
-Where salt and freshwater meet
-Where there are no strong tides or currents to prevent sediment deposition and accumulation
Eustatic change
When the sea level itself rises or falls
Isostatic change
When the land rises or falls, relative to the sea
Where does eustatic change occur
Globally, sea levels falling or rising
Where does isostatic change occur
Locally, areas of land sink or rise because of lost weight from ice in glacial periods
What part of the UK is sinking and which is rising?
-Scotland is rising
-South is sinking
Emergent coastal landforms (1)
Raised beaches
How are raised beaches formed
When wave-cut platforms rise above the sea level, raised beaches are formed
Submergent coastal landforms (2)
-Rias
-Fjords
How are rias formed
When low lying valleys become flooded due to higher sea levels
How are Fjords formed
When a glacier runs melts it runs out to see making a wide and deep U-shaped valley. When this floods a Fjord is formed
Fill in the gap: The _____________ is relatively shallow in fjords because of all the glacial sediment deposited there
Mouth of the river
What is the dalmatian coastline an example of?
It is a submergent coastline where a series of flooded valleys has caused a ria to be created
Thermal expansion
When water heats up it expands
Name the 6 different types of hard engineering strategies for coastal management
-Groynes
-Gabions
-Sea walls
-Rock armour
-Revetments
-Offshore breakwater
Groynes
Timber structures on beaches, built at right angles to the coast
Gabions
Metal baskets filled with rocks that absorb the energy from the waves
