Constructive waves tend to build up sediment on beaches through stronger swash movements that transport material upwards. Destructive waves erode beaches through stronger backwash movements that transport material downwards. Coastal sediments are transported alongshore through repeated up and down movement by swash and backwash in a zig-zag pattern that gradually moves the material in the direction of the prevailing waves and winds.

1. Coastal Geomorphology
The shape of the coast and its landforms is a
direct result of:
Geology + Marine processes + Sub-aerial processes + Man + (Climate)

2. Marine processes

3. Constructive waves
 These are depositional waves as they
lead to sediment build up, and are most
common where a large fetch exists.
 They tend to have a low gradient, a
larger swash than backwash, low energy
and an elliptical orbit.
 The wave period is long, with 6-8 waves
breaking in a minute.

4. Destructive waves
 These act as agents of erosion,
because backwash is greater than
swash.
 They are most common where
fetch is short, have a mainly
circular orbit, a steep gradient,
and 'plunge' onto the beach.
 The wave period is short, with 12-
14 waves breaking per minute.

5. Wave definitions
 Wave fetch: The distance of open water over which a
wave has passed. Maximum fetch is the distance from
one coastline to the next landmass, it often coincides
with prevailing wind direction (South West in the UK).
 Wave crest: Highest point of a wave.
 Wave trough: Lowest point of a wave.
 Wave height: Distance between trough and crest.
 Wave length: Distance between one crest/trough and
the next.
 Swash: Water movement up a beach.
 Backwash: Water movement down a beach.

6. Wave refraction
 It is very rare for waves to approach a regular uniform coastline, as most
have a variety of bays, beaches and headlands.
 Because of these features, the depth of water around a coast varies and as
a wave approaches a coast its progress is modified due to friction from the
seabed, halting the motion of waves.
 As waves approach a coast they are refracted so that their energy
is concentrated around headlands but reduced around bays. Waves then
tend to approach coastline parallel to it, and their energy decreases as
water depth decreases.

7. Discordant coastline

8. Concordant

9. Summary of coastal erosion
processes

10. Coastal erosion
Abrasion/corrasion:
 When waves approach the coastline they are carrying material such as sand, shingle, pebbles and
boulders. Abrasion occurs when this material is hurled against cliffs as waves hit them, wearing
the cliff away.
Hydraulic pressure:
 Cliffs and rocks contain many lines of weakness in the form of joints and cracks. A parcel of air can
become trapped/compressed in these cracks when water is thrown against it. The increase in
pressure leads to a weakening/cracking of the rock.
Corrosion/solution:
 Seawater contains carbonic acid, which is capable of dissolving limestone. The evaporation of salts
in seawater produces crystals and their formation can lead to the disintegration of rocks.
Sub-aerial:
 Coastal erosional processes that are not linked to the action of the sea. Erosion occurs via rain,
weathering by wind and frost. Its impact is often seen in soil creep, slumping and landslides.
Human activity:
 Much building and recreation occurs at the coast, and this increases pressure on cliff tops, making
them more liable to erosion and subsidence. The building of sea defences upsets the dynamic
equilibrium of the coastline.

11. Influences on the rate of
erosion
 The rate at which a stretch of coastline is
eroded is related to the following factors:
 The point at which the wave breaks - (if at the foot of a
cliff, the cliff is subject to maximum energy and most
erosion).
 Steepness of the wave.
 Depth of sea, fetch, aspect.
 Amount of beach material - (a wide beach protects a
cliff more than an arrow beach).
 Rock type and structure - (hard rock such as granite is
far more resistant to erosion than soft rocks, such as
clay).

12. The sub-aerial processes

13. Sub-aerial processes
Sub-aerial processes = weathering + mass
movement + humans*
Weathering = physical + chemical
Mass movement = falls + flows + slides + slumps + creep
*Pressure on cliffs (construction work)
Sea Defences (although designed to reduce erosion - in some
instances (e.g. the use of groynes) can increase erosion by
starving down stream areas of sediment

14. Weathering – basic summary
 Weathering Processes:
 Weathering is the breaking up of rock in situ
 Freeze-thaw processes (as water freezes and thaws in
cracks in cliffs, the expansion and contraction forces the
rock open, making them more susceptible to the action of
waves).
 Chemical weathering - water running down the face of
cliffs, either from surface runoff from above or from rainfall
can result in solution so that rock cracks are enlarged,
leaving the remaining rock loosened
Biological weathering - burrowing organisms and roots of
vegetation forces open cracks, making them more
susceptible to wave erosion) [NOT sub-aerial]
Human Activity

15. The weathering processes
Physical Weathering
Definition: Form of weathering responsible for the mechanical breakdown of rocks but involving no chemical change.
Forces acting on rock exposed on the Earth's surface open up any weak points in the rock and cause pieces to be broken off.
Piles of jagged rock fragments called scree are formed.
Freeze-thaw ( a fatigue process) Salt crystallisation Insolation weathering
↑ 9% on freezing. ↑ Volume not accretion In presence of H2O only – granular
7-15kg/cm2 (2115 kgcm-2 @ -22oC) Sedimentary more than igneous disintegration
Possibility of granular disintegration
Surface unloading (exfoliation) Hydration
Pressure release Water absorption – clays - kaolinite
e.g. SiO2 + 2H2O i Si(OH)4

16. The weathering processes
Chemical Weathering
Definition: Form of weathering brought about by chemical attack on rocks, usually in the presence of water. Chemical
weathering involves the breakdown of the original minerals within a rock to produce new minerals (such as clay
minerals, bauxite, and calcite).
Solution - the general term for chemical dissolving of rock minerals
Hydrolysis Oxidation Carbonation
•H+ ion - e.g. the hydrolysis of feldspars •O2 in gaseous form or dissolved in •CO2 + H2O → H2CO3 leads to
e.g. orthoclase feldspar produces clay water will reacts with metal ions; •CaCO3 + H2O → CO2 + Ca (HCO3 ) 2
minerals such as kaolinite,+ H+ and •Particularly significant on sedimentary
silicic acid. •4FeO + 3H2O + O2 → 2Fe2O3.3H2O rocks eg. Limestone and chalk of the
•Particularly significant on igneous Jurassic coast
rocks eg. Basalts of Northern Ireland

17. Sub-aerial processes
Mass Movement

18. Cliffs – erosional landform
Factors determining cliff formation
 Geological.
 Sub-aerial.
 Marine.
 Meteorological.
 Human activity.
The rule of thumb!
Cliffs are steep if removal of material at its base is
greater than supply.
Cliffs are shallow if the supply of material is greater
than removal.

19. Mass movement

20. Mass Movement
This is a combination of a rockfall &
earthflow

21. Types of cliff

22. Soft Geology Cliff
Fairlight Cove is mostly softer unconsolidated
rocks.
These rocks are less resistant to erosion &
landslips are common
Typical of NE England

24. Cliff & Wave Cut Platform
Wave attack constantly erodes the cliff base,
creating a Wave Cut Notch.
As the cliff is undercut, it collapses, leaving
rockfalls on the beach below.
As the cliff retreats it leaves behind a gently
sloping platform – Wave Cut Platform

26. Rotational Slumping
The full extent of (rotational)
slumping can be seen on the west
side of the cove.

27. Coastal transport
Coastal Transport
Weathering and erosion at the coast produces large amounts of material which is
moved along the coast line and out to sea by the action of waves.
Up and down the beach: Material is moved up the beach in the swash and back
down the beach in the backwash. Constructive waves move large amounts of
material up the beach as they have a strong swash, whereas destructive waves
move large amounts of material down the beach due to their strong backwash.
The movement of material by waves: The movement of material within the waves
themselves depends on (i) the size of the material and (ii) the energy available for
transporting the material. There are four possible types of transport within the
water:
Solution - material carried dissolved in the water
Suspension - fine material carried suspended within the water itself
Saltation - material which is too heavy to be continuously held in suspension is
bounced along the sea bed.
Traction - the heaviest material is simply rolled along the sea bed

28. Coastal transport
1. Waves break on
the beach at an
angle controlled by
the prevailing wind
direction. Material is
moved up the beach
in the swash.
2. Material then
moves straight back
down the beach in
the backwash under
the influence of
gravity.
3. As the processes
continues material
moves along the
coast in a zig-zag
movement.