Coasts - physical geography unit 2

What is a system?

A process or collection of processes that transform inputs into outputs

What are the 3 kinds of properties within a boundary of a system?

• elements ~ things making up the system (e.g plants)

• Attributes ~ characteristics of the elements that may be perceived or measured (e.g temperature)

• Relationships ~ associations occurring between elements and attributes

What is a coast?

The constantly changing interface between land and sea

• coasts are open systems

What does the term morphology mean?

The shape of the land

What are the 3 states of equilibrium?

• steady state equilibrium~ variations in energy and morphological response don’t deviate too far from LT average

• Metastases equilibrium ~ where environment switches from 2 or more states of equilibrium, stimulating a trigger

• dynamic equilibrium ~ a change in equilibrium conditions but in a much more gradual manner

What are the 4 factors causing beaches to exist in dynamic equilibrium?

• supply of sand

• Energy of waves

• Changes in sea level

• Location of shoreline

What do these 4 factors determine?

Whether a beach erodes or accretes (grows/ deposition)

What is back shore?

Area between high water marks and landward limit of marine activity

What is near shore?

From high water mark to where waves begin to break

What is offshore?

Area beyond point where waves cease to impact upon seabed and where activity is limited to deposition

What is foreshore?

Area between high water mark and low water mark and is important for marine processes

What is inshore?

Area between low water mark and point where waves cease to have any influence on the land beneath them

What is the breaker zone?

Area where waves approaching the coastline begin to break, usually where water depth is 5-10m

What is the surf zone?

Area between the ping where waves break, forming a foamy, bubbly surface and where the waves then move up the beach as wash in the swash zone

What is the swash zone?

Area where a turbulent layer of water washes up the beach following the braking of a wave

What are the characteristic features (e.g cliffs and stumps) of coastal environments created by?

• action of wind

• Waves

• Tides

• Sea currents

EROSION

What does mass movement mean?

Movement of material downhill due to gravity or rainfall e.g landslide

What is weathering?

Breakdown or decay of rock at or near earths surface, creating regolith (bits of rock) that remains in situ until moved my erosional processes (e.g mechanical, biological, chemical)

What is fetch?

The distance over which the wind blows over open water

What causes waves?

Wind blowing over the sea surface

What are the characteristic os constructive waves?

• low height

• Long length

• Low frequency (less than 10 a min)

• Low energy

• Main process is deposition

• Stronger swash

• Created lower beach profile gradient

What are the characteristics of a destructive wave?

• high height

• Short length Low frequency

• High frequency (over 10 a min)

• High energy

• Main process erosion

• Stronger backwash

• Creates steep beach profile gradient

Why do waves break?

• waves approach shallow water causing friction of the seabed to increase

• The bass of the wave begins to slow down

• Resulting in wave height and steepness to increase until upper part of it plunges forward and breaks into the shore

What is the beach wave cycle?

• most beaches have an alternating cycle of constructive and destructive waves

• Constructive waves build up the beach causing a steeper beach profile which encourages waves to become more destructive

• Destructive waves then move material back towards the sea making the beach profile flatter, encouraging waves to become more constructive

• This pattern repeats

What is the beach wave cycle an example of?

Negative feedback and links to beaches are on a constant state of dynamic equilibrium

What are the two types of beach?

• drift aligned → waves occurring diagonally towards the beach, causing long shore drift

• Wash aligned → waves occurring parallel towards the beach

What is wave refraction?

The bending of waves as they hit the coastline at an angle, causing uneven distribution of energy, influencing shape of coast through erosion and deposition

Where is an example of wave refraction?

Mavericks near Half Moon Bay on San Fransisco on the west coast of USA

• the high wave only occurs at certain times due to the waves hitting the rock reef at a certain angle to become massive

What are tides?

The periodic rise and fall in the level of the sea, caused by the gravitational pull of the sun and moon

What is the difference between a neap tide and a spring tide?

• Neap tide → tides that occur 2x a month when sun and moon are at right angles to earth

• Spring tide → tides that occurs 2x a month when sun and moon align os same side of earth

What is a storm surge?

A change in sea level away from the usual predicted tide level driven by weather systems e.g storms

What is tidal range?

The vertical difference in height of sea level between high and low tide

What are the 3 tidal ranges?

• macrotidal → over 4m

• Mesotidal → between 2m and 4m

• Microtidal → under 2m

What are the three types of currents?

• longshore currents (littoral drift) - waves approach at an angle and flow of water runs parallel to shoreline transporting water and sediment

• Rip currents - strong currents moving away from shoreline with a strong backwash

• Upwelling - movement from cold water in deep ocean towards surface → waves are nutrient rich and form part of global pattern of currents

What are ocean currents?

Large scale movements of water in the oceans

What are ocean currents caused by?

• Tides

• Winds

• Thermohaline circulation

What is thermohaline circulation?

• a process that occurs at both deep and shallow ocean levels

• The currents move much slower than local surface currents

• The currents affect the earths climate as it transports warm water from the equator and cold water from the poles around the world

How do currents affect us?

• important in shipping, fishing, safety

What is the coriolis effect?

• when earth rotates, circulating air is deflected towards the northern hemisphere and the southern hemisphere

How are trade winds made?

From the coriolis effect and atmospheric circulation

What are gyres?

Circular movements of ocean currents

What are the three sources of beach material?

Cliff erosion

Offshore

River

What are the two categories of coast?

High energy and low energy coasts

What are the characteristics of a low energy coast?

• not powerful waves

• Rate of deposition exceeds rate of erosion

• Landforms include beaches and spits

What are the characteristics of a high energy coast?

• powerful waves

• Rate of erosion exceeds rate of deposition

• Landforms include headlands, cliffs and wave cut platforms

What are the two factors affecting beach profile?

• sediment calibre (gradients)

• Type of wave

How do waves annd gradient affect beach profile?

• constructive waves move material up the beach → steeper gradient of beach

• Destructive waves move material down the beach→ gentle beach profile

What are the characteristics of a shingle beach?

• formed from constructive waves move material

• More percolation = less sediment removed via backwash = steeper gradient

What are the characteristics of a sand beach?

• formed from destructive waves move material

• Less percolation = more sediment moved via backwash = gentle gradient

What are the 5 beach features?

• beach scarp → cliff at point of high tide mark

• Berms → small ridges on sand

• Storm beach → accumulation of sediment at high tide mark

• Ridge and runnels → ridges with intervening depressions (runnels)

• Cusps → temporary semi circular depressions that only last one tide

What is a sediment cell?

A stretch of coastline, that is bordered by 2 prominent headlands

What are the sources of a sediment cell?

Inputs: rivers, coastal erosion

Transfers: littoral drift in direction of prevailing wind, moving sediment along coastline

What are the sinks of a sediment cell?

Stores: beach, sand dunes

Output: material from cell swept out to sea due to storm events

What is sedimentary budget?

A coastal management tool used to analyse and describe the different sediment inputs and outputs on the coast which are used to predict change at any coast over time

What is a positive budget?

More inputs than outputs to the system

What is a negative budget?

More outputs than inputs to the system

What is a spit and where do they form?

A stretch of sand/ shingle from mainland to the sea

They form on drift aligned beaches where there’s a sudden change in the shape of the coastline

What are cuspate forelands and where are they formed?

• they are described as 2 triangular beaches

• Formed by longshore drift moving sediment in opposite directions

• E.g dungness in Kent

What are tombolos and where are they formed?

• Is a spit that joins to an island

• Forms on drift and wash aligned coasts

• E.g Chesil beach on south coast of England

What are lagoons and where are they formed?

• formed behind bars

• Are shallows water separated from deeper water

What are offshore bar/ barrier island?

• are elongated ridges of sand/ gravel deposited beyond a shoreline by currents and waves

What is another name for weathering?

Sub aerial process

What is mechanical weathering?

• occurs in areas where there’s a large fluctuation in climate

• Freeze thaw occurs → water enters crack in rock, water freezes opening up the crack, rock eventually breaks into pieces

What is biological weathering?

• breakdown of rocks due to action of vegetation or coastal organisms

• Some marine organisms drill into rocks causing weakness in rocks

• Some plants attach to rocks and break parts loose

What is chemical weathering?

• oxidation → rocks dissolve when oxygen dissolved in oxygen reacts with minerals to form oxides

• Hydration → addition of water to minerals in rocks causes rocks to disintegrate

• Hydrolysis → acidic water comibines with minerals too create clays and dissolvable salts

• Carbonation → co2 dissolved in rainwater creates weak carbonic acid which reacts with calcium carbonate to make calcium bicarbonate that easily dissolves in water

what is mass movement?

• enlarged movement of sediment at the coastline

What are the 5 processes of mass movement?

• landslides

• Rockfalls

• Mudflows

• Rotational slips/ slumping

• Soil creep

What is rock fall?

• occurs when cliff in undercut from erosional processes on slopes affected by mechanical weathering

What is landslide?

• occurs In soft rock when bedding plane fails and triggered by rainfall

What is mudflow?

• heavy rains cause large flow of fine material downhill

• Causes soils to become saturated and percolation of water into deeper ground layers stop

• So, soils become fluid and flow downhill

What is rotational slips/ slumping ?

• occurs in areas where softer materials overlie more resistant materials

What are soil creeps?

• occurs where there is slow movement of particles down a slope

• Causes ripples to form

• Occurs in cold environments

What are the 4 processes of erosion?

• hydraulic action

• Abrasion

• Attrition

• Solution

What is hydraulic action?

Impact on the rocks from the force of the water which exerts lots of pressure, causing the rock to fracture

What are the 2 sub processes of hydraulic action?

• cavitation → when a breaking wave traps air in cracks in rocks as it hits the cliff face → creates lots of pressure and weakens rock

• Wave quarrying → high energy fall waves hit cliff face and removes large chunks of rock through vibration from the waves

What is abrasion?

Material that has been picked up by the sea wears away rock faces from it smashing against rock

What is attrition?

Rocks in a body of water crash into each other, which wears the rocks down in size and makes them more rounded

What is solution?

Is a form of chemical weathering and solution occurs in coastal zones with high rainfall. Effects from evaporation of salt water can erode rocks

What are some factors impacting erosion?

• wave steepness → the steeper the wave, the more energy they have so more erosive power

• Sea depth → rapid change in depth causes higher or steeper waves

• Beach presence → beaches act as natural barrier and absorbs wave energy

How does geology play a role in erosion?

The lithology of rocks can determine how much the rocks erode

E.g:

• igneous rocks made up of large crystalline structure helps it be resistant to erosion

• Sedimentary rocks made up of fine lamination of silt and mud which makes it more vulnerable to erosion

What are some examples of contrasting coastlines?

• concordance coastline → occurs when one single type of geology dominates coastline → means coastline more likely to erode

• Discordant coastline → occurs when rocks are perpendicular to coastline with a variation in geology → differential erosion more likely to occur

What are the 4 types of rock strata?

• horizontal strata → lead to steel sided cliffs

• Strata dipping away from coastline produces steep sided cliffs

• Strata dipping towards coastline porgies stepped cliffs → rocks slide down when undercut by waves

• Strata dipping more gentle angle to coastline produces cliffs with shallower angle → more slumping

What is psammosere?

A sand dune ecosystem

What is an ecosystem?

Plants and animals that adapt and adjust to abiotic (non living) and biotic (living) factors in a particular location

What is succession?

Change in species in an ecosystem over time

What is zonation?

A change in species over space

What is xerophite?

A plant adapted to living on a dry habitat like a sand dune

What factors influence sand dune formation?

• windy coastlines → wind blows sediment up the beach

• High tidal range have large expanses of sand that can dry out at low tide

• Offshore sand bars provide a source of sand

How are sand dunes formed?

• accumulations of sand gathered around obstacles (strandline)

• Sea brings sediment and wind moves it creating an embryo dune

• Tough plants take root on a dune stabilising it into place

• These plants die adding nutrients and humus to sand dune = more tougher plants can move in

• Climatic climax vegetation reached eventually

What are the types of dune that occur as you go up the beach?

1. Fore dune and mobile dune

2. Embryo dunes

3. Fore dunes

4. Grey dunes

5. Dune slack

6. Scrub and woodland

What are the adaptations of marram grass?

• woody tissue is tough and strong which gives the plant stability in winds

• Stems can grow quickly → good if plant covered in sand so plant can emerge

• Leaves have hairs that help leave to close and trap water in

What is a wave cut notch?

The area of the base of a cliff that has been eroded away → overtime cliff becomes more unstable causing it to collapse and create a gentle wave cut platform

How are wave cut plate forms coastal defences?

They cause wave along the coastline to break earlier, decreasing energy from wave at the base of the cliff

What is a geo?

A narrow steep sided inlet that opens from a line of weakness in a headland

What is a blowhole?

When a sea cave erodes through to the top of a headland