Coasts 2.1-2.4 Flashcards
Littoral zone
The highest sea level line to shallow offshore water
littoral zones (cells) in the UK
11 littoral zones
It is a closed system
How many worldwide live near coasts
Half the world’s population live within 200km of the coast
And 1 billion that live on the coast are at risk from flooding
Dynamic equilibrium
Inputs and outputs are balanced due to natural processes and interactions in it
Inputs in the coastal system
Marine - wave, tides, storm surges
Atmospheric - weather/climate
Land - rocks, tectonics
People - human activity and coastal management
Processes in the coastal system
Weathering Mass movement Erosion Transport Deposition
Outputs in the coastal system
Erosional landforms
Depositional landforms
Different types of coasts
Resistant rocky coastlines
Southwest of the UK
Can withstand Frequent winter storms
Not beaches
Coastal plains
Aka alluvial coasts
Waves are usually less powerful
Deposition exceeds erosion
Marine processes
Processes associated with the actions of waves
Erosion, transportation, deposition
Sub aerial processes
The processes of weathering and mass movement
Geology
The physical structure of rocks
4 types of transportation
Traction
Saltation
Suspension
Solution
Traction
Large boulders rolled along the seabed
Saltation
Pebble sized particles bounced along the seabed
Suspension
Small particles are carried in water
Solution
The dissolved material is carried in water
OR minerals in a rock dissolve under acidic conditions
The 3 types of erosion
Hydraulic
Abrasion
Attrition
Hydraulic action
Waves crash against the rock trapping air in the cracks and repeatedly shattering pieces off
Abrasion
Eroded sediment in the water scrapes against the rock removing small pieces
Attrition
Eroded sediment crash into each other
3 places deposition happens
In low energy zones
When water slows down
In bays
Constructive waves
Small height, long length Spilling Strong swash Weak backwash Build up beach
Destructive waves
Tall waves Short length Plunging Weak swash Strong backwash Destroy the beach
Hard engineering of coasts
Sea walls
Groynes
Gabions
Hard engineering Sea walls
Concrete walls curved to reflect energy back to sea
+ effective, give locals a promenade
- very expensive at £2000 a metre, can be eroded
Hard engineering Gabions
Rocks held in mesh cages for areas of erosion
+ cheap at £100 a metre, absorbs wave energy
- not strong and looks unnatural
Hard engineering Gabions
Wooden or rock structures at right angles to the sea
+they build up a beach with longshore drift
- starves beaches further down the coastline
Waves vs tide
Created by wind vs created by gravitational pull of the moon
They are unpredictable because wind is always changing vs they are predictable from moon’s orbit
Backshore area
This area experiences mainly physical processes
It is only affected by waves in very high tides and strong winds
Foreshore area
Aka swash zone
Waves break between high and low tide
This is where the beach is
Nearshore area
In the shallow water there is intense human activity and sediment is transferred by these currents
Estuarine coastlines
Found at the mouths of rivers
Extensive mud flats cut by channels
Exposed at low tide but inundates at high tide
At the backshore mud flats area vegetated - this forms a salt marsh
What is a rocky or sandy coast influenced by
Mainly influenced by geology and processes in the littoral zone
What is an emerging/submerging coastline determined by
It is determined by sea level change and tectonic uplift
3 things that affect erosion resistance
How reactive the minerals in the rock are
How many cracks, fractures, weaknesses the rock has
If the rocks are clastic
Scotland coastline case study
Scotland is still bouncing back, creating raised beaches
This is because it used to have a glacier weighing it down
This has meant the south coast of the UK is sinking in order to ‘even out’
Isostatic
The land moving relative to sea level
Effects are LOCAL
Eg. Glaciers pushing down or accumulation of sediment
Eustatic
The sea level itself is changing which affects the land
Effects are almost always GLOBAL
Eg. Climate change melting ice sheets and increasing sea level
Lithology
Strata Bedding planes Joints Folds Faults Dip
Horizontal strata
Produces steep cliffs
Rocks dip gently towards the sea
Almost vertical joints
Joints opened by weathering and pressure release
Steep dip towards the sea
Rock slabs slide down the cliff along bedding planes
Rocks dip inland
Well developed joints at right angles to bedding planes
Joints act as slide planes
Discordant coasts
Bands of more and less resistant rock run at right angles to the coast
More resistant rocks emerge at the coast as headlands and cliffs
Less resistant rocks form bays
Concordant coasts
More and less resistant rocks run parallel to the coast
Igneous rocks
Eg granite
Crystalline
Resistant
Impermeable
Sedimentary rocks
Formed in strata (layers)
Sandstone and limestone are permeable
Chalk is porous
Emergent coastlines
They are being produced by post glacial adjustment
Parts of the littoral zone where a fall in sea level exposed land once part of the sea bed
Landforms of emergent coastlines
Raised beach
-usually vegetated, flat surface covered by sand or pebbles
Fossil cliff
- sleep slope at the hack of a raised beach
- wave cut notches, caves, arches - marine erosion
Submergent coastlines
Sections of the littoral zone that have been flooded by ocean waters because of a relative rise in the elevation of sea level there
Features of submergent coastlines
River or glacially carved valley
Ria
Fjord
Dalmatian coastlines
Ria
A river valley at the coast that has been drowned by the sea
Fjord
A glaciated valley inundated by the sea
Dalmatian coastline
A series of longitudinal river valleys next to the coast that have been inundated
Anticlines and sinklines
Strata
Different layers of rock in an area and how they relate to each other
Deformation
The degree by which rock units have been deformed by tectonic activity
Faulting
The presence of major fractures that have moved rocks from their original positions
Lulworth cove formation
On a concordant coastline in Dorset, marine erosion broke through the resistant bed and rapidly eroded the wide cove behind
At the back of the cove is a bay and resistant rock which prevents further erosion
Why are headlands eroded more than bays
In deep water waves are parallel to one another
As waves approach shallow water offshore of a headland they slow down and wave height increases
In bays wave crests curve to fill the bay - wave height decreases
The straight wave crests refract, become curved, spread out in bays but concentrate on headlands
The overall effect concentrates powerful waves at headlands but lower wave crests in bays
Features found at a discordant coastline
Headlands and bays
Detached islands
Caves arches stacks stumps
Features found at a concordant coastline
Coves
Dalmatian coastlines
Half coastlines
Holocene period
Began 12,000 years ago at the end of the last ice age
Early stages marked by sea level rise of 35m and a warming climate
Dalmatian coast
An area is folded by tectonic activity into a series of anticlines and sync lines that run parallel to the coastline
The synclines have been drowned by rising sea levels - so there is a concordant coastline of long, narrow islands arranged in lines offshore
Dalmatian coast case study
Croatia
Drowned by sea level rise during the Holocene
Its geology is limestone (sedimentary)
Anticline
A ridge/bump of stratified rock
Syncline
A downward arc/fold of a rock layer
Haff coastline
Long sediment ridges that run parallel to the coast just offshore
Haffs created between the ridges and the shore
(This sediment was deposited as glaciers retreated at the end of the last ice age)
Low energy coastlines
Haff coastline case study
Southern fringes of the Baltic Sea
North Germany - Usedom
Cliff profile define
The height, angle and features of a cliff
Eg. Dipped, faulted, towards or away from the sea
The dip of rock strata
It is a tectonic feature, caused by plate movement
Horizontal layers in rocks can be tilted by tectonic forces
2 dominant characteristics for cliff profiles
The resistance to erosion of the rock
The dip of rock strata in relation to the coastline
Horizontal dip
Weak strata
Vertical or near vertical
More easily eroded
Landward dip
Steep profiles of 70-80degrees
Very stable cliff with reduced rock fall
High angle seaward dip
Sloping low angle profile
One rock layer faces the sea
Vulnerable to rocks sliding down the dip slope
Low angle seaward dip
Profile may exceed 90degres
Areas of overhanging rock
Very vulnerable to rock falls
3 Igneous rocks
Granite
Basalt
Dolerite
3 metamorphic rocks
Slate
Schist
Marble
3 sedimentary rocks
Sandstone
Limestone
Shale
Erosion rate - Igneous
Very slow
Strong, hard, erosion resistant
Few weaknesses to exploit
Erosion rate - Metamorphic
Slow
Resistant to erosion
But it has foliation and fractures
Erosion rate - sedimentary
Moderate to fast
The clastic and younger rocks are fast
They have bedding places and fractures
They are permeable
Diagram of the dunes
Composite cliff
Has rock from different geological periods
6 factors affecting rate of erosion
Dip Geology type Geological structure Sea level change Human management Wave type
Permeability and erosion
If a rock is permeable it allows water to flow through it
This water flow can weaken the layers of rock in the cliff by removing the cement that binds the layers together
So it makes erosion and recession more likely
What is a sand dune
A hill structure made of sand above the high tide mark
It is shaped by wind action
Parts are covered in grasses and shrubs
Where are coastal sand dunes found and why
They are found in drier countries where loose sand is blown by the wind in deserts and coasts
They need drier sand that is blown around often (not in tropical countries)
Biotic/abiotic factors
Biotic are living factors like the plant communities
Abiotic are non living factors like the environment itself
Psammosere
Aka succession
The way that the structure of sand dunes in a community develops over time
Pioneer stage of sand dunes
Seeds are blown about in the wind/washed up
Rooting conditions are poor
Wind moves sand in the dunes, rainwater soaks through rapidly
Sand is trapped by vegetation etc
Building stage of sand dunes
Plants trap sand and grow with it which binds it
Decaying pioneer plants make it fertile
The soil is less alkaline so less hardy plants grow
Stabilised by halophytic plants and roots
50-100 years
Final stage of sand dunes
Taller and more complex plants grow
Earlier stages’ plant die out (competition)
Water table nearly reaches the surface leading to dune slacks with plants that are water tolerant
Zonation
The variation of species or communities in and over an area
Eg. Salinity/height of water table leads to different species in different areas of the dune
Why is the first zone of sand dunes inhospitable
The sand is salty, dry, unstable and it lacks nutrients
Threats to sand dunes from people
Tourism and visitors to beaches
Climate change
Urbanisation of the coast (pedestrian and motorised pathways)
Introduction of invasive species
Sand dune blowout
Erosional dune landforms - depressions
A hole is created in the surface of the dune
Primary coasts
Dominated by land based processes
Eg deposition from rivers
Or new coastal land formed
Secondary coasts
Dominated by marine erosion or deposition processes
Marine erosion dominated
Steep face
Active undercutting
Limited cliff base debris
Subaerial process dominated
Curved slope profile
Lower angle face
Accumulated debris
Waves affecting beach morphology
Weather can determine wave type
Wave conditions can modify or create landforms
Types of sediment can be deposited or eroded
Removing debris from the cliff foot takes away the natural erosion barrier
How are waves formed
They are caused by friction between wind and water
If the wind is sustained from deep to shallow water, this forms a wave
There is orbital water particle motion in open water
When this reaches shallow water, there is an increase in wave height because it is shallower and the friction slows the bottom of the wave
4 things wave size depends on
The strength of the wind
The duration the wind blows for
Water depth
Wave fetch
3 things that change beach profiles
Sediment supply from rivers may be reduced
Coastal management may interfere with sediment supply
Climate change making an area sotrmier
Dune slacks
They result from blowout where erosion down to the water table has occurred
A large flat area of wet sand is exposed
The wind cannot pick up wet sand
3 things necessary for sand dunes
A supply of sand
Winds that transport the sand inland
A large inter tidal range
How does vegetation stabilise sediment
Roots make sediment bind together so it’s harder to erode
Plants provide a protective layer so the surface isn’t exposed
Friction with vegetation reduces the affect of wind speed
Storm beaches
Result from high energy deposition of very coarse sediment in the most severe storms
Berms
A result of shingle and gravel being deposited from summer swell waves
Offshore ridges
Formed by destructive wave erosion then these depositing sand and material offshore
