Coasts Flashcards
Define littoral zone
The wider coastal zone including adjacent land areas and shallow parts of the sea just offshore
(Exposed to the air at low tide and underwater at high tide)
How is Littoral zone divided
The zone is divided into different sections. The back shore and foreshore areas are where the greatest amount of human activity occur
Summer beach features (waves etc)
Summer waves are more gentle, constructive
Has wide berm
Winter beach features (waves etc)
Winter waves more harsh, destructive
Has:
Dune scarp
Steeper profile
Eroded or no berm
Bar
Short term factors
Individual waves, daily tides and seasonal storms
Long term factors
Changes to sea levels or climate change
Types of coastline (littoral zone)
Sandy beaches
Rocky cliffs
Coastal wetlands
Coastal inputs
People- human activity and coastal management
Marine- waves, tides, storm surges
Atmospheric- weather/climate, climate change, solar energy
Land- rock type and structure, tectonic activity
Coastal processes
Mass movement
Weathering
Erosion
Transport
Deposition
Coastal outputs
Erosional landforms
Depositional landforms
Different types of coasts
Classify coasts based on
Geology
Energy
Balance
Sea level
High energy coastline features
Very powerful waves
The rate of erosion is higher than the rate of deposition
High energy coastline erosional landforms
Headlands
Cliffs
Shoreline platforms
Tend to be found here
High energy coastline in uk
UK’s Atlantic facing coastline are powerful for most of the year (Cornwall and
High energy type of coastline
Rocky coasts are generally found in a high energy environment
Low energy coastline features
Less powerful waves
The rate of deposition is higher than the rate of erosion
Low energy coastline depositions landforms
Beaches
Spits
Coastal plains
Low energy coastline UK
Stretches of the uk coast where waves are not powerful or the coast is sheltered from large waves
Igneous features
Earths oldest rocks, formed in lava and deep magma.
The rocks were once molten, then cooled and crystallised.
Most of these rocks are resistant to erosion.
E.g. giants causeway
Sedimentary features
Formed from sediments eroded and deposited by rivers, the sea or sea bed
Some are resistant
Metamorphic features
Originally sedimentary rocks but have been heated and compressed during igneous activity
Heating and compression harden them and make them resistant shale becomes slate, limestone becomes marble
Field sketches
Identify key features
Annotated with labels
It helps you to remember what you saw
Opportunity to apply key terminology to a real place
Considerations with field sketches
Weather conditions
Fit for purpose
Scale
Relief
Concordant coastline
Bands of more resistant and less resistant rock run parallel to the coast
Features: cove and bay
Examples: lulworth cove, kimmeridge bay
Discordant coastline
Geology alternates between bands of more resistant and less resistant rock run perpendicular to the coast
Cliff
Vertical (near vertical), marked change in gradient exposure of rock or other materials. Often forms the barrier between land and sea
Mass movement
The shifting of rocks and loose material down slope under the influence of gravity
Structure
The way the rocks are geologically arranged, including layering and bedding planes
Coastal recession
Coastal erosion
Joints
Fractures, caused either by contraction as sediments dry out, or by earth movements during uplift
Strata
Layers of rock
Dip
The angle at which rock strata lie (horizontally, vertically, dipping towards the sea or dipping inland)
Lithology
The physical characteristics of particular rocks
Coastal morphology
The shape and form of coastal landscapes and their features
Bedding planes
These are natural breaks in the strata, caused by gaps in time during periods of rock formation
Folds
Formed by pressure during tectonic activity, which makes rocks buckle and crumple (Lulworth crumple)
Faults
Formed when the stress or pressure to which a rock is subjected, exceeds its internal strength (causing it to fracture). The faults then slip or move along fault planes
Submergent coastline
Those that have been flooded due to a rise in sea levels at that location
E.g. Dalmatian coast (Croatia) or pacific coasts (southern chile)
Emergent coastline
Formed where water level has fallen, or land has risen due to tectonic activity. This happens due to isostatic change
The morphology of a coastline will be determined by
The lithology or physical characteristics of the rock
The relief and the slope
The rock type
The permeability of the rock
How hard/ soft the rock is and it’s resistance to erosion
The resistance of a rock is determined by:
How reactive minerals are to chemical weathering
Whether rocks are clastic or crystalline
The amount of cracks, fractures and fissures which can be exploited by weathering
Geology
Earth science concerned with solid earth, the rocks its composed with and processes by which they change over time
Lithology
The make up of each individual rock type, includes physical structure and chemical composition
Structure
The way the rocks are geologically arranged. Including layering and bedding planes
Chalk geology, lithology, structure
G- chalk
S- uniform
L- alkaline rock, resistant, lithology
Sandstone geology, lithology, structure
G- sandstone
S- horizontal bedding planes
L- small crystals moderately resistant
Mixed geology, lithology, structure
G- mixed
S- mixed
L- varies from small crystals to dense interlocking crystals
Relief
Cliff profiles are subject to marine processes such as wave erosion as well as sub aerial processes
Cliff structure: uniform layers
Rockfall occur on hard rock cliffs with horizontal bedding planes. Rock blocks are dislodged by weathering and fall to the cliff face
Horizontal strata produce
Steep cliffs
E.g. Alan bay, isle of wight
Rocks dip gently towards the sea, with almost vertical joints
Joints opened by weathering and pressure release
Release slabs to form cliffs dipping seawards
Steep dip towards sea
Rock slabs slide down the cliff along bedding planes
Form steep seaward dipping cliffs
Rocks dip inland
Produces a stable, steep cliff profile
Rocks dip inland
Well developed joints at right angles to bedding planes
Joints act as slide planes. Produce slide planes
The geology and lithology at the coast affects the speed at which it erodes
- igneous rocks are crystalline, resistant and impermeable. E.g. granite
- sedimentary rocks are formed in strata. e.g. Limestone Jointed sedimentary rocks are permeable. Other sedimentary rocks have air space between the particles (porous) e.g. marble + schist
- metamorphic rocks are very hard, impermeable and resistant
- unconsolidated materials are loose, such as the boulder clay of the holderness coast, they are not cemented together and are easily eroded
Rates of erosion
Geology and lithology, weathering and mass movement will affect the rate of erosion
Erosion rate
Glacial till. Holderness coast. 1-10m/year
Sandstone. Devon. 1cm-1m/year
Limestone. Dorset. 1mm-1cm/year
Granite. Cornwall. 1mm/year
Other factors that affect rate of erosion
High energy waves
Absence of a beach
Rising sea levels
Coastal management/ sea defences elsewhere along the coast
MOHs hardness scale
The relative hardness of rocks can be measured using the mohs hardness scale. It works by seeing if the rock or mineral would be damaged by other objects.
Scale: 1-10 (10 hardest)
Coastal recession
Refers to how fast a coastline is moving
Influenced by many factors such as the lithology or rock type
Different types of rock erode at different rates due to different characteristics
Waves caused by
Friction between wind and water
Why waves break
When out in open water there is little horizontal movement of ocean water, the bulk of the motion is up and down or vertical. However, this changes slightly when waves approach the coastline. As the water approaches the coastline it encounters increasing contact with the shelving sea bed, which exerts a frictional force on the base of the wave. This changes the normal circular orbit of the wave into an elliptical orbit. As the waves get closer and closer to the coast the impact of friction grows, with the top of the wave moving faster than the base of the wave. Eventually a critical point is reached where the top of the wave (the crest) curves over and creates a breaking wave. This breaking wave can be further disrupted by water returning down the coastline back out to sea.
Destructive wave
Result of locally generated wind
High amplitude, short wavelength
High frequency of 10-14 waves per minute
Strong backwash, weak swash removes a lot of material from the beach producing a steeper beach profile
Force of destructive waves can fire material to back of beach
Constructive wave
Short amplitude and long wavelength
Low frequency of around 6-8 per minute
Waves have been generated far offshore creating a gradual increase in friction and thus a gradual steepening of the wave front
Creates spilling breaker, where water movement is elliptical
Swash surges up gentle gradient with maximum energy
Traction
Sediment rolls along, pushed by waves and current
Saltation
Sediment bounces along, either due to the force of water or wind
Suspension
Sediment is carried in the water column
Solution
Dissolved material is carried in the water as a solution
Current
Flows of sea water in a particular direction driven by winds, water density, salinity or temperature.
Stabilising depositional landforms
Made up of sand and shingle which is loose and unstable
Plant succession bind the loose sediment together and encourage further deposition
Vegetation can help to trap and stabilise sediment - became vulnerable when vegetation is weakened
Sediment budget
The amount of sediment available within a cell
Sediment budget increases
More deposition is likely.
Negative feedback
Sediment budget falls
Waves continue to transport sediment. One change has lead to another change.
Positive feedback
Dynamic equilibrium
The whole balance of the cell system
Wave dominated processes
Shore platforms
Cliffs
Beaches
Spits
Deltas
(High energy)
Tide dominated processes
Mudflats
Sand flats
Salt marshes
Mangroves
Deltas
(Low energy)
How does headland affect incoming waves
Headlands force the incoming waves to refract or bend- concentrating their energy at the headland. This increases the waves erosive power, which leads to a steepening of the cliffs and their eventual erosion into arches and stacks
How does bays affect incoming waves
When waves went enter a bay their energy is dissipated and reduced. This leads to the deposition of sediment forming a beach
When are constructive waves more common
More common in summer. So the beach profile is steeper
When are destructive waves more common
Winter. The beach profile is not as steep
Factors causing beach profiles to change over long periods of time
Sediment supply
Coastal management
Changes to the climate
How does sediment supply cause beach profiles to change over long periods of time
Sediment supply from rivers could reduce the construction of dams on river upstream
How does coastal management cause beach profiles to change over long periods of time
Coastal management in one place reducing the sediment supply further along the coast
How does changes to the climate cause beach profiles to change over long periods of time
Global warming could make the UK climate stormier causing more destructive waves and ‘winter’ beach profiles would become more common
Open system
Open to inputs and outputs in terms of energy and matter
How can sediment be brought into a sediment cell
Sediment can be brought into cell by eroding sea, cliff, river transport, sand dunes, continental shelf off shore through waves
Sub aerial processes
Weathering
Mass movement
Define weathering
Gradual breakdown of rock, close to ground surface
Define mass movement
Movement of weathered material downslope as a result of gravity
Define sub aerial
Land based processes which alter the shape of the coastline.
Types of mass movement
Rockfall
Translational slide
Slump / rotational slide
Topple
Flow
Define rockfall
Strong, jointed and steep rock faces are exposed to mechanical weathering. Occur on slopes over 40 degrees. The material either bounces or falls vertically to form scree
Define translational slide
An increase in the amount of water can reduce friction which causes sliding. In a rock or landslide, slabs or rocks/blocks can slide over underlying rocks along a slide or slip plane
Define slump/rotational slide
Moderate or steep slopes. Common where softer materials overlie more resistant, impermeable rocks. Causes rotational scars on land and repeated slumping causes terraced cliff profiles
Define topple
Rock strata have a steep seaward dip, undercutting by erosion will quickly lead to instability and blocks of material falling seaward
Define flow
Increase in amount of water can reduce friction and cause mud and earth to flow over underlying bedrock. In a flow the material becomes jumbled up.
Long term sea level change
Sea level varies over time it is measured relative to land so the relative sea level can change if either the land or the sea falls or rises
Two types of sea level change
Eustatic change
Isostatic change
Define eustatic change
When the sea level itself rises or falls
How has tectonic events impacted some coasts as well as sea level
Local tilting of the land
The uplift of mountain ranges and coastal land at destructive and collision plate margins
Define Marine regression
Where the sea level drops and produces an emergent coastline
Define Marine transgression
Where the coastline is flooded it produces a submergent coastline
Marine regression eustatic fall in sea level
During glacial times, when ice sheets form on land in high latitudes, water evaporated from the sea is locked up on land as ice
Global sea level falls
Marine regression isostatic fall in sea level
Weight of ice sheets causes earths crust to sink
As it melts the land slowly lifts out of the sea
Marine transgression eustatic rise in sea level
End of glacial period, melting ice returns water to sea causes sea levels to rise globally
Thermal expansion causes sea level rise
Marine transgression isostatic rise in sea level
Land can ‘sink’ at coast due to deposition of sediment
Happen in large river deltas where weight of sediment deposition causes delta subsistence
Isostatic changes to sea level
Process by which Earth’s crust seeks to reach equilibrium following loading or unloading by ice
Define glacial maximum
The point where the ice reached to
How is raised beach formed
Beach deposits and shell beds would have been formed when the sea was previously at a higher level and has now fallen
How are rias formed
‘Drowned’ river valleys which have been (partially) submerged during a period of marine transgression
Once sea levels begin to rise again, the deepened segments of the river situated at the coast are filled as sea level increases creating drowned valkeh
How are Dalmatian Coasts formed
Formed on concordant coastline where geological strata, hills and mountains run parallel to the shore
How are fjords formed
Drowned glacial valley which have been shaped by the action of ice and submerged during Holocene
Define Fjords
Very deep and straight channel- interlocking spurs were
Define isostatic change
When the land rises or falls, relative to the sea
Define coastal retreat
Coast moving inland
Holderness coast short term physical factors
Longshore drift
Clay particles- fine and easily transported by suspension. Don’t build up on beach
Narrow and offer little friction to absorb wave energy
Tide flow southward transport sand by longshore drift
Leaves cliff poorly protected
Holderness coast medium term physical factors
Geology- mainly boulder clay
Mixture of fine clays, sands and boulders deposited by glaciers
Structurally weak, little resistance to erosion
Chalk band that surrounds boulder clay has created headland
Holderness coast long term physical factors
Fetch- exposed to north east waves fetch (500-800km- not very big)
Increase size + power:
- current (swell) means powerful destructive waves
- low pressure weather systems + storms
- small, enclosed seas generate huge waves during storms
- sea floor relatively deep so no friction weakening them
Holderness coast medium term human factors
Coastal management
Higher rates of erosion occur south to the coastal defences
Sea wall, groynes, rock armour at Hornsea protect part of the coast but it interrupts flow of longshore drift. Beach down drift at Hornsea, Mappleton are starved of material- 4m of cliff eroded each year
Holderness coast long term human factors
Coastal management and land use- different stakeholders: central government agencies, local government in local economy, environmental stakeholders
Mainly agricultural land use
Sea wall built in Hornsea 1870- lasted 6 yeard
What year was the Bangladesh storm surge
Cyclone sidr
2007
Bangladesh development
LIC
Population of 156 million
142 in global HDI ranking
GDP of $150 billion
Improved disaster prevention measures (improved forecasting and warning system and the use of cyclone shelters) made casualties lower than expected
Bangladesh background on weather event
Strong winds= 223km/h
Category 4 storm
Storm surge height = up to 6m
Bangladesh social impacts
Dead and missing = 4234
Injured = 55,282
The sanitation infrastructure was destroyed, raising the risk of disease
Electricity supply and communications were knocked out, roads and waterways became impassable
Drinking water was contaminated by debris, and many freshwater sources were inundated with salt water
Severe flooding in low lying areas
Bangladesh economic impacts
Cost of damage to roads, embankments, sluice gates and riverbank protection= US$29.6 million
Total cost = US1.7 billion
The high winds and floods damaged housing, roads, bridges and other infrastructure
Damaged educational institution = 16,954
Bangladesh environmental impacts
The storm surge breached many coastal and river embankments
Damaged crops = 685,528 hectares
Cattle and poultry killed = 1,778,507
UK development
HIC
Population of 64.1 million
14 in HDI ranking
GDP of $2.7 trillion
