The coastal system
Coasts are natural systems – they have inputs, outputs, flows and stores of sediments and
energy
1. Inputs = sediment can be brought into the system in many ways
a. Rivers carry eroded sediment (clastic sediments) into the coastal system from
inland
b. Sea level rise can flood river valleys, forming estuaries. Sediment in the
estuary becomes part of the coastal system
c. Sediment is eroded from cliffs, by waves, weathering and landslides
d. Sediment can be formed from the crushed shells of marine organisms
e. Waves, tides and currents can transport sediment from offshore deposits
(e.g., sandbanks)
2. Outputs = sediment can be washed out to sea, or deposited further along the coast
3. Flows/transfers = processes of erosion, weathering, transportation and deposition
can move sediment within the system (e.g., from beach to dune)
4. Stores/components = landforms such as beaches, dunes and spits
Energy sources
- Wind = winds are created by air moving from areas of high pressure to areas of low
pressure. Strong winds generate powerful waves
- Waves = waves are created by the wind blowing over the surface of the sea. The
friction between the and the surface of the sea gives the water a circular motion.
o Wave height is affected by the wind speed and the fetch of the wave
o As waves approach the shore they break. This is caused by friction.
o There are two types of wave:
Constructive waves = have a low frequency, long and low, powerful
swash which carries material up the beach and deposits it
Destructive waves = high and steep, high frequency, strong backwash
removes material from the beach
- Tides = tides are caused by the gravitational pull of the moon and the sun
o They are long periods waves that appear to move through the oceans due to
gravitational forces exerted by the moon and sun
o Spring tides – earth and sun are aligned (high tide)
o Neap tides – sun and moon are at right angles to the earth (low tide)
o Tides increase the rate of coastal erosion
- Currents = a current is the generated flow of water in one direction. Currents move
material along the coast
Sediment cells = areas along the coastline and in the nearshore area where the movement
of material is largely self – contained
Way waves erode the coastline:
1. Corrasion (abrasion) – bits of rock and sediment transported by the waves smash
and grind against rocks and cliffs, breaking bits off and smoothing surfaces
, 2. Hydraulic action – air in cracks in cliffs is compressed when waves crash in. the
pressure exerted by the compressed air brakes off rock pieces
3. Cavitation – as waves recede, the compressed air expands violently, exerting
pressure on the rock and causing pieces to break off
4. Wave quarrying – the energy of wave when it hits the cliff break off rock
5. Solution – soluble rocks get dissolved by the seawater
6. Attrition – bits of rock in the water smash against each other and break into smaller
bits
Transportation processes
1. Solution – dissolve and then are carried in the water
2. Saltation – larger particles are carried in suspension
3. Suspension – very fine material, is whipped up by the turbulence and carried along in
the water
4. Traction – very large particles are pushed along the seabed by the force of the water
5. Longshore drift - Sediment is moved along the beach, due to prevailing winds
which alter the direction of the waves. This allows sediment to be
transported from one section of coastline (as an output) to another stretch
of coastline (as an input)
Rip currents are powerful underwater currents occurring in areas close to the
shoreline on some beaches when plunging waves cause a buildup of water at the
top of the beach. The backwash is forced under the surface due to resistance
from breaking waves, forming an underwater current. Rip currents are an energy
source in a coastal environment and can lead to outputs of sediment from the
beach area.
High-energy coastlines are associated with more powerful waves, so occur in
areas where there is a large fetch. They typically have rocky headlands and
landforms and fairly frequent destructive waves. As a result these coastlines are
often eroding as the rate of erosion exceeds the rate of deposition.
Low-energy coastlines have less powerful waves and occur in sheltered areas
where constructive waves prevail and as a result these are often fairly sandy areas
. There are landforms of deposition as the rates of deposition exceed the rates of
erosion.
Mechanical (Physical) Weathering:
● Freeze-thaw (Frost-Shattering): Water enters cracks in rocks and then the water
freezes and expands in volume causing cracks to develop
● Salt Crystallisation: As seawater evaporates, salt is left behind. Salt crystals will
grow over time, forces the cracks to widen. Salt can also corrode ferrous rock
● Wetting and Drying: Rocks such as clay expand when wet and then contract
again when they are drying and these cycles cause the rocks to break up
Coasts are natural systems – they have inputs, outputs, flows and stores of sediments and
energy
1. Inputs = sediment can be brought into the system in many ways
a. Rivers carry eroded sediment (clastic sediments) into the coastal system from
inland
b. Sea level rise can flood river valleys, forming estuaries. Sediment in the
estuary becomes part of the coastal system
c. Sediment is eroded from cliffs, by waves, weathering and landslides
d. Sediment can be formed from the crushed shells of marine organisms
e. Waves, tides and currents can transport sediment from offshore deposits
(e.g., sandbanks)
2. Outputs = sediment can be washed out to sea, or deposited further along the coast
3. Flows/transfers = processes of erosion, weathering, transportation and deposition
can move sediment within the system (e.g., from beach to dune)
4. Stores/components = landforms such as beaches, dunes and spits
Energy sources
- Wind = winds are created by air moving from areas of high pressure to areas of low
pressure. Strong winds generate powerful waves
- Waves = waves are created by the wind blowing over the surface of the sea. The
friction between the and the surface of the sea gives the water a circular motion.
o Wave height is affected by the wind speed and the fetch of the wave
o As waves approach the shore they break. This is caused by friction.
o There are two types of wave:
Constructive waves = have a low frequency, long and low, powerful
swash which carries material up the beach and deposits it
Destructive waves = high and steep, high frequency, strong backwash
removes material from the beach
- Tides = tides are caused by the gravitational pull of the moon and the sun
o They are long periods waves that appear to move through the oceans due to
gravitational forces exerted by the moon and sun
o Spring tides – earth and sun are aligned (high tide)
o Neap tides – sun and moon are at right angles to the earth (low tide)
o Tides increase the rate of coastal erosion
- Currents = a current is the generated flow of water in one direction. Currents move
material along the coast
Sediment cells = areas along the coastline and in the nearshore area where the movement
of material is largely self – contained
Way waves erode the coastline:
1. Corrasion (abrasion) – bits of rock and sediment transported by the waves smash
and grind against rocks and cliffs, breaking bits off and smoothing surfaces
, 2. Hydraulic action – air in cracks in cliffs is compressed when waves crash in. the
pressure exerted by the compressed air brakes off rock pieces
3. Cavitation – as waves recede, the compressed air expands violently, exerting
pressure on the rock and causing pieces to break off
4. Wave quarrying – the energy of wave when it hits the cliff break off rock
5. Solution – soluble rocks get dissolved by the seawater
6. Attrition – bits of rock in the water smash against each other and break into smaller
bits
Transportation processes
1. Solution – dissolve and then are carried in the water
2. Saltation – larger particles are carried in suspension
3. Suspension – very fine material, is whipped up by the turbulence and carried along in
the water
4. Traction – very large particles are pushed along the seabed by the force of the water
5. Longshore drift - Sediment is moved along the beach, due to prevailing winds
which alter the direction of the waves. This allows sediment to be
transported from one section of coastline (as an output) to another stretch
of coastline (as an input)
Rip currents are powerful underwater currents occurring in areas close to the
shoreline on some beaches when plunging waves cause a buildup of water at the
top of the beach. The backwash is forced under the surface due to resistance
from breaking waves, forming an underwater current. Rip currents are an energy
source in a coastal environment and can lead to outputs of sediment from the
beach area.
High-energy coastlines are associated with more powerful waves, so occur in
areas where there is a large fetch. They typically have rocky headlands and
landforms and fairly frequent destructive waves. As a result these coastlines are
often eroding as the rate of erosion exceeds the rate of deposition.
Low-energy coastlines have less powerful waves and occur in sheltered areas
where constructive waves prevail and as a result these are often fairly sandy areas
. There are landforms of deposition as the rates of deposition exceed the rates of
erosion.
Mechanical (Physical) Weathering:
● Freeze-thaw (Frost-Shattering): Water enters cracks in rocks and then the water
freezes and expands in volume causing cracks to develop
● Salt Crystallisation: As seawater evaporates, salt is left behind. Salt crystals will
grow over time, forces the cracks to widen. Salt can also corrode ferrous rock
● Wetting and Drying: Rocks such as clay expand when wet and then contract
again when they are drying and these cycles cause the rocks to break up
