Geography- Coasts

what is the definition of a coast?

The zone where the land meets the sea.

The narrow zone where the land and sea overlap and directly interact

What is the Foreshore?

The area lying between the high water mark (HWM) and low water mark (LWM).

It is the most important zone for marine processes in times that are not influenced by storm activity 

What is the offshore?

the area beyond the point where the waves stop impacting the seabed

where activity is limited to deposition of sediment. 

What is inshore?

The area between the LWM and the point where the waves cease to have any influence on the land beneath them. 

What is nearshore?

The area extending seaward from the HWM to the area where the waves begin to break.

It includes the swash, surf and breaker zone. 

What is the backshore?

The area between the HWM and the landward limit of marine activity.

Changes normally only take place here during storm activity

What is the breaker zone?

The area where waves approaching the coastline begin to break

usually where the water depth is 5 to 10m 

What is the swash zone?

the area where a turbulent layer of water washes up on the beach following the breaking of a wave 

What is the surf zone?

the area between the point where waves break, forming a foamy, bubbly surface

where the waves then move up the beach as swash in the swash zone

What is a closed system?

Nothing added or lost from the system

E.g. Earth

What is an open system?

inputs and outputs come in and out of the system.

(e.g. water entering in precipitation and leaving through evaporation) 

What is dynamic equilibrium?

When a systems inputs and outputs are equal

When the equilibrium is disturbed, the system undergoes self regulation to restore the dynamic equilibrium.

usually achieved by negative feedback

Give examples of Coast inputs

Precipitation

Wind energy

Wave energy

Tidal energy

Current energy

Give examples of coast stores

Sediment held in sand dunes

Sediment held on the beach

Sediment held in cliffs

Give examples of transfers at coasts

Transpiration

Evaporation

Deposition

Erosional processes

Give examples of outputs at coasts

Sediment moved offshore or inshore away from the coastal zone

Landslides, slumping, rock falls

Describe climate as a control in the coastal system

having more wind would move more sediment away from the system.

High temperatures (climate change) will cause more water to evaporate.

Precipitation adds more water to the system.

Drought could lead cliffs to break up.  

Describe geology as a control in the coastal system

resistant geology would have big cliffs and arches

less resistant rocks would have sand dunes and a flat coast line, with depositional land forms.  

Describe rock structure as a control in the coastal system

discordant coastline

concordant coastlines  

Describe sea level as a control in the coastal system

sea levels rising (submergent coastline) would cause more erosion and the flooding of coastlines.

Sea levels falling (emergent coastlines) would reveal more landforms

what are the types of energy in the coastal system?

waves

wind

currents

tides

Describe atmosphere

weather, precipitation, storms, wind, temperature  

describe the impact of tectonics at coasts

volcanic sand and new rocks

tsunamis

earthquakes (mass movement

isostatic change (change in the height of the land)

describe the ecosystems at coasts

sand dunes

salt marshes

ocean ecosystems 

Describe oceanic impact at coasts

sediment

currents (erosion)

Describe the oceanic features at Dyrholaey, Iceland 

Waves are responsible for the active erosion and deposition on the coastline.

Winds coming from Antarctica, causes very strong winds on the coastline.

Nothing sheltering the coastline.

Wind transfers black sand and pebbles to the coast.

Sea level change (recently dropped) has created isolated remnants of coast landforms  

Describe the tectonics features at Dyrholaey, Iceland

the black sand and pebbles are volcanic basalt formed by tectonic activity. 

describe the ecosystems at Dyrholaey, Iceland

vegetation has developed on newly exposed surfaces

wildlife has developed, especially birds

Where does coastal sediment come from?

Streams and rivers

estuaries

cliff erosion

offshore sand banks

What are sediment cells?

Areas where inputs and outputs are balanced. (closed systems)

along the coastline of England and Wales 

How are the boundaries of sediment cells distinguished?

Separated by well- defined boundaries

such as headlands and stretches of deep water.  

Explain how it is unlikely that sediment cells are closed systems

Small and fine sediment is able to find its way around the headlands into neighbouring cells.  

Why have sediment cells been divided into smaller sub-cells?

allows them to be studied closely

more controlled management 

What is the coastal budget?

The balance between the sediment being added and removed from the coastline system (each individual cell)  

Describe rivers as a source of sediment?

Accounts for majority of coastal sediment

especially areas of high rainfall

active river erosion

Describe cliff erosion as a source of sediment

important in areas of soft geology

Landslides

mass movement

Describe longshore drift as a source of sediment

Sediment transferred from one stretch of coastline to another

e.g. between sediment cells

Describe wind as a source of sediment

Wind blown sand can be deposited in coastal regions

Describe glaciers as a source of sediment

Glaciers can carve into the sea

chunks of ice break off

sediment trapped in ice in deposited

Describe offshore as a source of sediment

Sediment can be transported by waves onshore

if sea levels rise, coarse sediment can be rapidly transported to form landforms (e.g. barrier beaches)

storm surges also bring in large amounts of sediment

what is positive feedback?

Where a flow/ transfer leads to increase or growth

What is negative feedback?

Where a flow/ transfer leads to decrease or decline

Give examples of positive feedback forms

Beaches

sand dunes

salt marches

spits

Give examples of negative feedback forms

cliffs (erosion)

beaches

What is the angle of exposure?

range of wind direction an area of coast is exposed to. 

larger angle= stronger wind

What is a fetch? 

The distance of open water over which the wind blows uninterrupted by major land obstacles.

Higher fetch would increase the strength of wind

What is the prevailing wind direction in the UK?

South West

Describe the UK’s climate in terms of global atmospheric circulation

strong pressure gradient

winds blow in from the high pressure to the south and towards the low pressure in the UK

What does low pressure cause?

Air rises

Rain

What does high pressure cause? 

air sinks

What are Aeolian processes?

• processes at the coastline relating to or arising from the action of the wind

• e.g. Energy of the winds, amount of wind erosion (abrasion), the amount of wind deposition

What things effect the size of waves?

• Strength of the wind,

• The depth of the water

• fetch

What is the trough?

The lowest point of a wave?

What is a crest?

The highest point of a wave

what is a swash?

The water moving up towards the beach

What is a backwash? 

The water moving back out to sea

How is wavelength calculated?

The distance between two wave crests

How is wave height calculated?

The distance between a crest and a trough of a wave

How are waves formed?

1. The wind blows over the wave

2. The waves move in a circular way out at sea  

3. The water becomes shallower and it begins to move in an elliptical way

4. the waves slow down due to friction

5. The waves begin to topple over

describe constructive waves

• low wave height

• frequency of waves is 6-8/min

• wavelength= long (up to 100m)

How do constructive waves break onto the beach?

The front steepens, giving a gentle spill onto the beach 

Describe the swash characteristic of a constructive wave

Rapidly loses volume and energy as water percolates through beach material  

Describe the backwash characteristics of constructive waves 

Weak backwash- insufficient force to pull sediment off the beach  

What effects do constructive waves have on beach shape?

Beach material builds up

Describe destructive waves

• high wave height

• frequency is 10-14/min

• short wavelength

How do destructive waves break onto the beach?

Rapidly steepen and when breaking they plunge down 

What are the swash characteristics of destructive waves?

The swash is inhibited from the next wave

Describe the backwash characteristics of destructive waves 

Powerful backwash with little forward movement 

What are destructive waves impact on beach shape?

steepens the beach profile

Describe how waves interact with the bay and headland

• The waves hit the coastline and once they reach the headland they lose energy, causing the waves to crash.

• Water to the side of the headlands continues to move forward towards the bay, causing erosion.

• This leads the headland to become steeper.  

describe longshore/ litterol drift

• Wind approaches at an angle.  

• Wind causes swash to be at angle. (takes sediment up at an angle)  

• Backwash moves sediment straight back with it – due to gravity  

• Groynes trap sediment  

what is a rip current?

strong currents moving away from the shoreline. They develop when seawater is piled up along the coastline by incoming waves  

how do u identify a rip current?

• an area where no waves are breaking

• Carves a trench underneath the water 

• The water will appear deeper and darker

• can look rough on the surface

describe upwelling

• Surface winds blow across water  

• Warm surface water is blown away  

• Deeper colder water is pushed upwards to replace warm water 

How are tides created?

• caused by the gravitational pull of the moon and sun

• Each day there are 2 high tides and 2 low tides. There are about 12 hours and 25 minutes between two high tides.

Describe a spring tide

• Sun, moon and Earth are in alignment 

• This causes a stronger gravitational pull on the earth 

• This causes bulges on either side of the earth  

• This causes big differences in the tides  

• Moon is closer to the Earth so it has a stronger gravitational pull  

Describe a Neap tide

High tide won't be as high, low tide won' t be as low- smaller tidal range  

what is macrotidal?

more than 4 meters

What is mesotidal?

2-4 meters

What is microtidal?

less than 2 meters

what is a storm surge? 

• Caused by hurricanes  

• Sea level is far above the normal tide  

• Air rises- low pressure- rain  

• Water pulled upwards  

How does tidal range influence the coastline?

• More opportunities for erosion to occur (e.g. wave cut platform)  

• Smaller tidal range- more opportunities for coral reef to develop 

• More aeolian processes due to more of the beach being exposed 

• More opportunities for sub-ariel weathering with a large tidal range  

What is an amphidromic point?

• the point where the tidal range is zero

• past this point the tides become more extreme

• position of them depends on the configuration of the land and sea, ocean depth and sea floor topography

What are cotidal lines?

• The lines coming out from the amphidromic point

• represent the differences in tides in hours

what is hydraulic action?

• power of the waves as they smash onto a cliff.

• trapped air is blasted into holes and cracks in the rocks

• causes the rock to break apart

What is cavitation?

• surface collapse of air bubbles found in flows of water

• the bubbles cause micro-jets of water which travel at high speeds with great pressure

• produces extreme stress in rock

What is wave quarrying? 

• the action of waves breaking against unconsolidated material- e.g. sand and gravel

• waves scoop out loose material 

What is corrasion?

• fragments of rock being picked up and hurled by the sea at the cliff

• often during storms

What is abrasion?

• sandpapering effect of rocks grinding over a rocky platform

• causes it to become smooth

What is solution? 

• socks dissolved by seawater

• calcium based rocks broken down by the chemicals of sea waer 

what is attrition?

• rocks knock against one another causing them to become smoother and more rounded

Which factors cause higher erosion at a coast?

• higher waves

• long fetch

• deep then suddenly shallow water

• no beach presence- more erosion of cliffs

• less resistant rock

• lack of coastal defences

• shingle beaches

Which factors cause less erosion at a coast? 

• shorter waves 

• short fetch 

• shallow sea

• beach presence- absorbs energy instead of cliffs 

• resistant rocks 

• coastal defences 

what is surface creep? 

wind rolls or slides along the surface- occurs where sand is exposed to wind (e.g. low tides) 

Describe freeze thaw

• Water enters the cracks of rocks and freezes with cold temperatures 

•  The water expands as it freezes by 10%- meaning the ice occupies more space in the rock.  

• Pressure builds up in the crack of the rock and widens.  

• This causes pieces of rock to eventually break off.  

describe pressure release

• Originally under immense pressure  

•  As the overlying mass is unloaded from a rock it develops weaknesses and cracks.  

• This makes the rocks susceptible to erosion and weathering due to weaknesses 

• When the weight has gone, cracks form  

describe biological weathering 

•  Includes processes that lead to the breakdown of rocks.  

• Active on coastlines  

• Particularly active in areas with chalk geology  

• Seaweed attaches itself to rocks and the action of the sea can lead to rocks being pried off of the sea floor. 

• Some organisms secrete chemicals which can break down rocks  

• Some animals also weaken cliffs by burrowing into them.  

describe chemical weathering

• Common on coasts- occurs where rocks are exposed to air and moisture 

• Solution is the main chemical process and it combines with erosion to produce many distinctive features 

describe oxidation

• causes rocks to disintegrate when the oxygen dissolved in water reacts with rock minerals  

• This forms oxides and hydroxides 

• It especially effects ferrous, iron-rich rocks  

• It can be seen by brown/yellow staining on the rocks surface.  

describe hydration 

• makes rocks more susceptible to chemical weathering 

• Involves the physical addition of water to minerals in the rocks  

• This causes rocks to expand, leading to stress and the rock to disintegrate  

• This weakens the rock and can create cracks and widen joints- allowing further chemical weathering