Coasts
The Coastal Zone
Globally over 1 billion people live near coasts that are at risk of flooding and roughly half the world’s
population live with 200km of the coast. This is because coasts provide access to fishing grounds,
trade and energy sources. The littoral zone refers to the part of a sea, lake or river closest to the
coast and can be divided into distinct sections:
Backshore: the area of land above the influence of waves and the high tide mark.
Foreshore: The area between high and low water mark, which includes the surf zone where waves
break.
Inshore: the area between the low water mark where waves cease to have any effect on the land
beneath them.
Offshore: the area beyond the point where waves have any effect and activity is limited to sediment
deposition.
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Factors that affect the coastline:
Vegetation: Vegetation can either help stabilise landforms or increase biological weathering.
Human Interference: Erosion is not a problem until it threatens humans and human built defences
can limit erosion.
Rock type: Harder rock types are less likely to erode.
Fetch of the wave: the further the wave travels, the powerful it is and the more it erodes.
Weather conditions: storms increase erosion rates and strong winds create more powerful waves.
Freeze-thaw weathering also has an effect on coastlines.
The Coastal System
The coastal zone is constantly changing due to the large number of processes acting within it. As an
open system, it has inputs, stores, transfers/processes and outputs. The inputs can be divided into
marine, atmospheric, land-based and human inputs and describe how sediment or energy is brought
into the system. Processes describe how sediment is transferred around the system through
processed like weathering, mass movement, transportation and deposition. The outputs are
erosional or depositional landforms and the creation of different types of coast, depending on other
parts of the system.
The balance between the inputs and the outputs of the system creates an equilibrium which is
maintained through positive and negative feedback loops. Positive feedback is a change which
causes a domino effect, exacerbating the initial change, and negative feedback is a change which
causes an event which reverses the initial change.
There are three main types of coastal landscape: rocky, sandy or estuarine. Landscape refers to the
visible features of an area on a large scale and while all coastlines can be divided into similar zones,
,not all have the same landscapes. Rocky coastlines have an abrupt transition from land to sea and
have an exposed rocky platform at low tide, for example Flamborough Head on the Holderness
Coast. Sandy coastlines have a beach which is covered at high tide and sand dunes which are not,
the dune vegetation stabilises the coastline and prevents erosion, for example the sandy beaches of
East Anglia. Estuarine coastlines have a gradual transition from land to sea and extensive mudflats
which are exposed at low tide. They often have a close backshore which is vegetated, creating a salt
marsh, for example Yealm Estuary in Plymouth. Coastlines can be divided into low or high energy
environments.
Low energy coast High energy coast
Waves & Weather Constructive waves with a Destructive waves with a long
short fetch. fetch
Calm weather Storm conditions
Processes Deposition and transportation Erosion transportation, mass
Longshore drift and nearshore movement and weathering.
currents Offshore currents
Landscapes Sandy and estuarine currents. Rocky coastlines
General Location Sheltered bays and lowland High relief/ rocky landscapes.
coast.
Rocky coastlines are high energy, primary coasts and are often emergent, meaning they are made up
land which was previously below sea level. They are microtidal, with tides of less than 2m and are
advancing. Sandy or Estuarine coastlines are low energy, secondary coasts are submergent, meaning
they are made up of land, which is now below sea level, but was once above. Sandy coastlines are
mesotidal, with tides of 2-4m and estuarine coastlines are macrotidal, with tides of more than 4m,
and both are retreating.
Geology has a large impact on coastal landscapes and landforms as different rocks are affected by
processes to different degrees. There are three main types: sedimentary, igneous and metamorphic.
Sedimentary: formed from deposits of pre-existing rocks or organisms accumulating on the Earth’s
surface . They often have distinct layering or bedding.
Metamorphic: started out as another rock but have been fundamentally changed from their original
rock type. They form under intense heat and/or pressure – conditions found deep within the earth
or at tectonic plate boundaries.
Igneous: form when molten rock crystallises and solidifies, deep within the earth near active plate
boundaries and then rises to the surface. They can be divided into two groups, intrusive or extrusive.
Geology and Lithology.
The two key aspects that influence coastal landscape systems are lithology, the general physical and
chemical characteristics of rocks, and structure, which refers to rock properties like bedding,
jointing, faulting and folding. Lithology impacts rates of coastal recession, particularly in bedrock.
Igneous rocks are mostly crystalline and resistant to weathering and marine erosion – they erode at
a rate of less than 1cm per year. Metamorphic rocks are formed under intense heat and pressure,
which makes them very hard, impermeable and resistance – they erode at a rate of around 0.1 to
0.3 cm per year. Sedimentary rocks are formed in strata, and are often porous, with some containing
chemicals which react with rain to dissolve the rock – they erode at a rate of around 0.5 to 10cm per
, year. Unconsolidated materials are loose and easily eroded – they erode at a rate of around 2 to
10m per year.
Permeability is an important factor in influencing rates of coastal recession as groundwater can
weaken rocks or create high pore pressure, which can affect the stability of cliffs. Permeable rocks
allow water to flow through them due to being porous or having numerous joints. They are less
resistant to weathering because water percolating come into contact with a large surface area that
can be chemically weathered. When permeable rocks are laid over impermeable rocks groundwater
accumulated in the top layer, saturating it and forming a spring, leading to fluvial erosion. When
impermeable rocks are laid over permeable rocks, groundwater flows over the interface removing
the cement that binds together and causes the layers to slump. Water percolating through
permeable rock can produce pore water pressure, pushing rock particles apart, reducing friction and
lubricating lines of weakness, affecting the cliff’s overall stability.
Coasts can be classed as concordant or discordant. In concordant coastlines, the rock strata run
parallel to the coastline. Over time the sea erodes the more resistant rock to reach the less resistant
rock behind it, which is easily eroded, forming bays and coves. Dalmatian and Haff coastlines are
examples of concordant coasts. The Dalmatian coast of Croatia has been formed from limestone
folded by tectonic activity into a series of anticlines, ridges, and synclines, dips, that trend parallel to
the coastline. Haff coastlines are formed when deposition produces unconsolidated landforms
parallel to the coastline. These spits and bars, and the subsequent lagoons formed behind them,
were formed from material deposited during the ice age being pushed to landwards as the sea rose.
Discordant coastlines are made up of rock strata which runs perpendicular to the coastline. These
alternating bands of soft and hard rock create a series of bays and headlands. The morphology of
these coastlines alters the distribution of wave energy and rate of erosion through wave diffraction.
Wave refraction is convex in bays, dispersing energy, and concave in headlands, concentrating
energy. This generally decreases the degree of indentation.
Different geological structures have different formations and impacts on coastal morphology:
Joints: A fracture dividing rock into two sections that have not moved away from each other. It
increases erosion rates by creating fissures which can be exploited by processes like hydraulic action.
Faults: cracks across which the rock has been offset. Huge forces are required to crack and displace
the rock and faults can extend kms. They increase rates of erosion.
Folding: bends in the rock which are created when sedimentary rocks are squeezed by tectonic
forces. The overwhelming pressure often make rocks buckle and crumple. The increased number of
joints in the rock increase erosion rates.
Bedding planes: layers of horizontal rock which form lines of weakness which can be more easily
eroded. Dip refers to the angle of inclination of the layer form the horizontal, and can have dramatic
effects on cliff profile.
