Coasts Flashcards
What’s the littoral zone?
Wider coastal zone including adjacent land areas and shallow parts of the sea just offshore
Features and processes at the backshore?
Features- Beaches, dunes, rockfalls
Processes- Atmospheric, sub aerial erosion, human activity
Features and processes at the foreshore?
Features- Inter tidal zone, sand ridges
Processes- Marine, wave tides, storm surges
Features and processes at the nearshore?
Features- Longshore bars, sand
Processes- Marine, waves, tides, storm surges
Features and processes at the offshore?
Features- Offshore sand
Processes- Marine, tides
Ways to classify coasts?
- Geology
- Energy
- Balance
- Sea level
- Formation processes
- Tidal range
What waves occur at low energy coasts?
- Less powerful
- Calmer conditions
- Short fetches
What waves occur at high energy coasts?
- More powerful
- Storm conditions
- Long fetches
What processes occur at low energy coasts?
- Deposition and transport
- Sediments from rivers, longshore drift
What processes occur at high energy coasts?
- Erosion and transport
- Sediments from eroded land, mass movement and weathering
What landforms are at low energy coasts?
- Beaches
- Spits
- Salt marshes
What landforms are at high energy coasts?
- Cliffs
- Wave cut platforms
- Arches
What is the general location of low energy coasts?
- Sheltered from large waves
- Lowland coasts
What is the general location of high energy coasts?
- Exposed to largest waves
- Rocky landscape
Example of a low energy coast?
- Mediterranean sea coasts
- East Anglican coast
Example of a high energy coast?
- Atlantic coasts of Norway and Scotland
- Pacific coasts of Alaska and Canada
Are discordant coastlines parallel or perpendicular?
Perpendicular
Are concordant coastlines parallel or perpendicular?
Parallel
How are coves formed?
From bands of hard rock being penetrated for whatever reason e.g. weathered which allows the sea to reach the soft rock eroding it away to form a cove
What are dalmatian coastlines and an example?
-Type of concordant coastline
- Valleys and ridges run parallel to one another, when the valleys flooded due to a rise in sea level, the tops of the ridges remain above the surface of the sea as a series of offshore islands that run parallel to the coast
- E.g. the Dalmatia coast in Croatia
What are haff coastlines and an example?
- Type of concordant coastline
- Formed in low energy environment where there is deposition of muds and sands
- Long sediment ridges topped by sand dunes run parallel to the coast just offshore, creating lagoons between the ridges and the shore
- Southern Baltic Sea the Neman Haff
What is a bedding plane?
Natural breaks in the strata, caused by gaps in time during periods of rock formation, it creates horizontal cracks
What are joints?
Fractures, caused either by contraction as sediments dry out, or by earth movements during uplift, creates vertical cracks
What are folds?
Formed by pressure during tectonic activity, which makes rocks buckle and crumple
What are faults?
Formed when the stress or pressure to which a rock is subjected, exceeds its internal strength
How are igneous rocks formed, examples, and erosion rate?
Through the cooling and solidification of magma or lava, basalt, granite, very slow erosion rate, often with few joints
How are metamorphic rocks formed, examples, and erosion rate?
When the original rock is subjected to heat causing physical damage, slate, marble, slow erosion rate, often folded and heavily fractured
How are sedimentary rocks formed, examples, and erosion rate?
The subsequent cementation of minerals or organic particles, sandstone, shale, fast erosion rate, younger rocks tend to be weaker as more bedding planes
What are permeable rocks?
Allow water to flow through them, and include many sandstones and limestones
What are impermeable rocks?
Do not allow groundwater flow and includes clays, mudstones and most igneous and metamorphic rocks
What is unconsolidated sediment?
Sediment that is not ‘linked’/not ‘put together’
What coastlines are protected from erosion of unconsolidated sediment?
- Coastal sand dunes
- Coastal sand marshes
- Coastal mangrove swamps
What are halophytes?
Plants that can tolerate salt water
What are xerophytes?
Plants that can tolerate very dry conditions
How does vegetation stabilise coastal sediment?
- Roots of plants bind soil together which helps to reduce erosion
- When completely submerged, plants provide a protective layer for the ground and so the ground is less easily eroded
- Plants reduce the wind speed at the surface and so less wind erosion occurs
Process of salt marsh succession
- Algal stage- Gut weed and blue green algae establish as they can grow on bare mud which their roots help to bind together
- Pioneer stage- Cord grass and glasswort grow, their roots begin to stabilise the mud allowing the estuarine to grow
- Establishment stage- Salt marsh grass asters grow, creating a carpet of vegetation and so the height of the salt marsh increases
- Stabilisation- Sea thrift, scurvy grass and sea lavender grow, and so salt rarely ever gets submerged beneath the marsh
- Climax vegetation- Rush, sedge and red fescue grass grow since the salt marsh is only submerged once or twice a year
Process of plant succession
- On coasts where there is
a supply of sediment and deposition occurs, pioneer plants begin to grow in bare mud and sand - Due to the salty soil conditions only certain plants can grow there
- As more deposition occurs and
the vegetation dies and releases nutrients into the sand this reduces the saltiness of the soil - This means different plants can start growing there
- These processes continue over time allowing new
species of plants to colonise
How is marram grass a good example of a pioneer plant?
- Tough and flexible
- Adapted to reduce water loss
- Roots grow up to 3m deep and can tolerate 60 degrees
Where are salt marshes found?
- Creeks and edges of estuaries
- Behind a spit
- Sheltered bays
Why may beach profiles change over time?
- Sediment supply from rivers is reduced
- Interference in sediment supply along the coast as a result of coastal management having impacts further down
- Climate change may make destructive waves more common
Characteristics of constructive waves?
- Low energy
- Deposition
- Summer
- Finer sediment
- Strong swash
- Weak backwash
Characteristics of destructive waves?
- High energy
- Erosion
- Winter
- Larger sediment
- Weak swash
- Strong backwash
What is a storm beach?
A steep, coarse-grained beach formed by severe storm waves
What is a berm?
A raised, nearly horizontal ridge of sand or gravel that forms parallel to the shoreline on a beach, created by wave action depositing material above the average high tide level
What is an offshore ridge?
Elevated strip of land, usually composed of sand or sediment, that runs parallel to the coastline but is located underwater
When will most erosion occur?
- Waves are at their largest
- Waves approach at 90 degrees to the cliff face
- The tide is high
- Heavy rainfall weakens cliff
What is hydraulic action?
Forcing water and air into joints and bedding planes
What rocks are vulnerable to hydraulic action?
Heavily jointed sedimentary rocks
What does abrasion affect?
Suitably loose sediment has to be available, sedimentary rocks are more vulnerable than igneous
What does attrition affect?
Softer rocks
What does corrosion affect?
Limestone, which is vulnerable to solution by weak acids
How is a wave cut platform formed?
- Waves break against the cliff face
- The waves erode the cliff face through abrasion and hydraulic action
- The cracks break off bits of rock
- The notch becomes larger and larger
- The notch enlarges into a cave
- The roof of the cave collapses due to pressure
- The cliff retreats inland
- The backwash carries away the eroded material
- A wave-cut platform is left behind
How is a cave arch stack and stump formed?
- Cracks: Waves erode cracks in the headland through abrasion and hydraulic action
- Caves: The cracks widen into caves as waves grind away at the rock
- Arches: Caves that form in a headland may eventually break through to the other side, forming an arch
- Stacks: The arch’s roof collapses due to erosion and gravity, leaving a stack of rock
- Stumps: The base of the stack is eroded until it collapses, forming a stump
What is suspension?
Carrying fine particles, like silt and clay, in a river or body of water
What is traction?
Large, heavy rocks rolling or sliding along the bottom of a river
What is saltation?
Small rocks and pebbles bounce along the bottom of a river or sea bed
What is solution?
When water dissolves minerals from rocks
How is a spit formed?
A spit is a long, narrow beach extension that forms when waves deposit sediment along a coastline. This happens when there’s a change in the coastline’s direction, such as at a river mouth or estuary
How is a tombolo formed?
Forms after longshore drift carries sediments across a gap between the mainland and an island, forming a narrow low ridge of sand
How is an offshore bar formed?
Forms in shallow water, where destructive waves break before reaching the beach, these waves scour the seabed and throw material forward into a heap
How is a cuspate foreland formed?
Forms when significant longshore drift is from opposite directions along a coast, so that sediment is deposited across a bay from both directions, forming two spits, and eventually these two spits meet
What are the 3 components of the sediment cell model?
- Inputs
- Transfers
- Stores
What are some examples of inputs in the sediment cell model?
- Cliff erosion
- Eroding depositional features e.g. spits
- Erosion of wave cut platforms
What are some examples of transfers in the sediment cell model?
- Longshore drift
- Currents
What are some examples of stores in the sediment cell model?
Permanent storage:
- Offshore bar
- Estuary
Temporary stores:
- Beaches
- Spits
What happens if the sediment budget falls?
Erosion will increase, positive feedback
What happens if the sediment budget increases?
Deposition will increase, negative feedback
What is weathering?
In-situ breakdown of rocks by chemical, mechanical or biological agents
What is erosion?
Breakdown of rock due to the action of some external force which transports the eroded material to a new location
What is mechanical weathering?
The breakdown of rocks due to exertion of physical forces
Explain freeze thaw weathering
Water enters cracks in rocks and then the water freezes
overnight, this increases pressure on the rock creating cracks which grow making the cliff more vulnerable to other processes of erosion
Explain salt crystallisation
As seawater evaporates, salt is left behind, salt crystals will grow over time exerting pressure on the rocks forcing cracks to widen
What is ‘wetting and drying’ related to weathering
Rocks such as clay expand when wet then contract again when they are drying, frequent cycles of wetting and drying at the coast can cause these rocks and cliffs to break up
What is chemical weathering?
Breakdown of rocks through chemical reactions
What is carbonation?
Rainwater absorbs CO2 from the air to create a weak carbonic acid which then reacts with calcium carbonate in rocks to form calcium bicarbonate which can then be easily dissolved
What is oxidation?
When minerals become exposed to the air through cracks and fissures , the
mineral will become oxidised which will increase its volume (contributing to mechanical
weathering), causing the rock to crumble
What is solution?
When rock minerals such as rock salt are dissolved
What is biological weathering?
The breakdown of rocks due to the actions of plants, bacteria and animals
How do plant roots contribute to biological weathering?
Roots of plants growing into the cracks of rocks, which exerts pressure eventually splitting the rocks
How do birds contribute to biological weathering?
Some birds such as Puffins dig burrows into cliffs weakening them and making
erosion more likely
What is a rockfall?
- Steep cliff
- Rock fragment may bounce off cliff or fall straight
What are the causes of a rockfall?
- Mechanical weathering
- Marine erosion
- Geological structure
- Seismic activity
What are the processes of a rockfall?
- Rock weakened
- A section of rock detaches
- Gravity makes it fall
What is slumping?
When a section of cliff moves downslope in a curved motion
What are the causes of slumping?
- Weak rock or unconsolidated material
- High water content
- Waves undercutting base
What are the processes of slumping?
- Rainwater infiltrates material
- Weight of the water saturated material causes it to be heavy
- Slumps downwards
What is mudflow?
A fast moving flow of water saturated soil
What are the causes of a mudflow?
- Heavy rainfall
- Deforestation
- Steep slopes
What are the processes of a mudflow?
- Rain saturates soil
- The soil loses cohesion and becomes fluid
- Gravity pulls the saturated soil downslope
What is soil creep?
The slow, gradual downslope movement of soil particles and other surface materials
What is the cause of soil creep?
Repeated expansion and contraction of soil due to wet-dry cycles
What are the processes of soil creep?
- Soil absorbs water and expands at right angles to the slope
- During dry conditions, it contracts vertically, moving slightly downslope
What are landslides?
A downslope movement of rock among a straight slip plane, the rock maintains contact with the slope as it moves
What are the causes of landslides?
- Mechanical weathering
- Marine erosion
- Geological structure
What are the processes of landslides?
- Weathering weakens rock layers across a bedding plane
- Heavy rain lubricates the slip plane, reducing friction
- Marine erosion undercuts the base removing support
- Gravity pulls downwards
What is solifluction?
A type of flow in permafrost regions where the thawed upper layer of soil moves over frozen ground
What are the processes of solifluction?
- In summer, the top layer of permafrost thaws
- The thawed layer becomes saturated and slides over the impermeable frozen ground
- The landscape develops lobes of flowing sediment
What is thermal contraction?
The shrinking or decrease in size of a substance as its temperature decreases
What is thermal expansion?
Where an object expands and becomes larger due to an increase in its temperature
What is an eustatic change?
Involves a rise or fall in water level caused by a change in the volume of water, affecting all the world’s connected seas and oceans
What is an isostatic change?
Local rise or fall in land level, for example during glaciation ice connected on land which created extra weight to press down on to the land causing it to sink, and as the ice melted, the land began to rebound to its original position
What is a eustatic fall in sea level (marine regression)?
During glacial periods when ice sheets form on and in high latitudes, water evaporated from the sea is locked up on land as ice causing a global fall in sea level
What is an isostatic fall in sea level (marine regression)?
During the build up of land based ice sheets, the weight of the ice causes the earth’s crust to sag, when the ice melts, the land surface slowly rebounds upwards over years, slowly lifting the land surface out of the sea
What is a eustatic rise in sea level (marine transgression)?
At the end of a glacial period, melting ice sheets return water to the sea causing the sea level to rise globally
What is an isostatic rise in sea level (marine transgression)?
Land can ‘sink’ at the coast due to the deposition of sediment, especially in large river deltas where the weight of sediment deposition leads to very slow crustal sag
What is a ria and how is one formed?
A flooded river valley
- During an ice age some land areas were not covered with ice but had frozen ground, so rivers carved valleys with steeper sides than normal
- After ice melted, sea levels rose and drowned the mouths of these valleys
What is a fjord and how is one formed?
A flooded glaciated valley
- During an ice age, glaciers eroded U shaped valleys, down to the coast of the time and then, after the ice melted, the sea level rose again and flooded into the valley
What is a fjard and how is one formed?
A flooded inlet with low rocky banks on either side
- Formed by post glacial drowning of glaciated lowland rocky terrain
- E.g. Gulf of Finland
What is a raised beach and how is one formed?
A former beach or wave-cut platform that is now located above the current sea level, formed by a relative fall in sea level or uplift of the land
What is a fossil cliff and how is one formed?
A near vertical slope
- Initially formed by marine processes but now some distance inland
What components can affect sea level rise?
- Glaciers
- Thermal expansion
- Ice sheets
How can mass movement leave the coast more vulnerable to retreat?
Moves sediment to the base where transportation processes move the sediment away, exposing the cliff
How is wind direction and fetch an influence of coastal recession rates?
- Links back to waves
- Short term
- Increased rate if blowing directly onshore
- Large fetch increases the rate
- Dominant wind generally matches longest fetch
Difference between dominant and prevailing winds
Dominant= more powerful
Prevailing= most common
How do tides influence coastal recession rates?
- Increased rate with higher tides
As there is deeper water in the foreshore and so more energy in the backshore
How do storms influence coastal recession rates?
- During destructive waves there is an increased rate
- Global warming increases frequency and severity
How do seasons influence coastal recession rates?
- Links to storms as they are more likely in the winter
- Cyclones in the summer
How do weather systems influence coastal recession rates?
- Interaction between warm and cold air masses produce anticyclones and depressions
What is rip rap and positives and drawbacks of it?
Large igneous/metamorphic boulders which break up and dissipate wave energy
+ Cheap to maintain
- Dangerous
- Intrusive
- Rocks are difficult to transport
What is a sea wall and positives and drawbacks of it?
Concrete/steel reinforcements that act as a physical barrier to absorb wave energy
+ Effective
+ Often have a promenade
- Expensive
- Intrusive
What are groynes and positives and drawbacks of them?
Vertical stone or timber fences which trap sediment to prevent longshore drift
+ Works with processes (doesn’t prevent coastal processes)
+ Builds up the beach
- Terminal groyne syndrome
- Unattractive
What are revetments and positives and drawbacks of them?
Stone timber or concrete which absorbs wave energy and reduces erosion on dune and mud banks
+ Relatively cheap
- High maintenance
- Unnatural looking
What are offshore breakwaters and positives and drawbacks of them?
Large igneous/metamorphic boulders which forces waves to break offshore
+ Effective
+ Reduces wave energy
- Navigation hazard
- Unattractive
What is beach nourishment and positives and drawbacks of them?
Adding sediment to an existing beach
+ Increases in tourist potential
+ Relatively cheap and easy to maintain
+ Natural and blends in
- Constant maintenance
- Not as effective as some hard engineering solutions
What is cliff stabilisation and positives and drawbacks of it?
A method to reduce erosion involving reducing the angle, adding wadding or removing water to prevent landslides
+ Cost effective
+ Can work on loose sediment
- Can dry out and collapse
What is dune stabilisation and positives and drawbacks of it?
Planting marram grass to stabilise the dunes
+ Cheap
+ Sustainable
+ Provides habitats
- People may not stay off the area
- Time consuming
What are some economic and social reasons people may stay by the coast?
- Trade
- Fishing
- Tourism
- Scenery
- Fertile soil
- Transport
How does sea level rise risk deltas?
Sea level rise poses a significant threat to river deltas, causing land loss, flooding, and saltwater intrusion, primarily because deltas are low-lying areas that rely on sediment from rivers to maintain their height and resist the rising sea
How is coastal flooding made worse?
- Drop in air pressure
- When strong winds push waves onshore
- When there are high or spring tides at the same time as storm
- If coastline narrows into funnel shape
