Coastal Systems and Processes

coastal systems and processes are responsible for shaping the coastline

Coastal environments are complex systems that involve the interaction of various factors, including the marine environment, natural environment, climate, biosphere, fluvial frameworks, structural processes, and human development and management. This all takes place within a small segment of the land/ocean interface known as the coast. Each coast is unique in its location and set of functions. Understanding these interactions can be challenging, but by using a systematic approach to geological reasoning, it is possible to gain a deeper understanding of how coastal forms develop and how these processes continuously shape them.

The essentials of coastal systems and processes

The three main marine processes that influence coastlines are erosion, transportation, and deposition. Erosion refers to the breaking down of land by the power of waves. Waves and tides play a role in the transportation of this broken-down material to other areas, and deposition refers to the process where waves and tides lose energy and no longer carry the disintegrated material. Each coastline has its own balance and equilibrium of erosion, transportation, and deposition, which is affected by various interactions. Therefore, we can classify coastlines as being erosion- or deposition-dominated.

The four different ways that waves and tides erode the coast are indicated below: 

Hydraulic action: Air becomes trapped in joints and cracks in the cliff face. When a wave breaks, the trapped air is compressed, which weakens the cliff and causes erosion.

Abrasion: Pieces of rock and sand in waves are thrown against the cliff face. Over time, they wear down the cliff surface like sandpaper.

Attrition: Waves crush rocks and stones on the shore against each other, causing them to break and become smaller and smoother.

Solution: Weak acids present in ocean water can dissolve certain types of rock, such as chalk or limestone.

There are four different ways that waves and tidal flows transport material: 

Solution: Minerals dissolve in ocean water and are carried in a mixture. The load is not visible. The material can come from cliffs made of chalk or limestone, and calcium carbonate is carried along in the mixture.

Suspension: Small particles are carried in water, such as sediment and clay, which can make the water appear cloudy. Flows collect sediment in suspension during a storm when high-force winds produce high-energy waves.

Saltation: The material bounces along the ocean floor, such as small pieces of shingle or large sand grains. The current cannot keep larger and heavier sediment suspended above water for extended periods.

Traction: Stones and larger sediment are moved along the ocean floor.

Sediment Cells

The processes of erosion, transportation, and deposition within the coastal zone are largely contained within sediment cells or littoral cells. It is believed that there are 11 large sediment cells in England and Wales (right). A sediment cell is generally considered to be a closed system, meaning that sediment is not transferred from one cell to another. The boundaries of sediment cells are determined by the geography and state of the coastline. Large landforms, such as the Llyn Peninsula in Wales, provide significant natural barriers that limit the movement of sediment. However, in reality, it is unlikely that sediment cells are completely closed, with variations in wind direction and tidal flows. It is inevitable that some sediment is moved between cells. Additionally, there are many smaller-scale sub-cells within the larger cells.

Paces of Erosion 

Erosion rates vary depending on a variety of factors. One important factor to consider is the type of wave and the distance a wave has to travel. The fetch of a wave is the distance a wave travels in open water from its origin to the point where it breaks. The larger the fetch, the longer the time the wind has to affect the waves, resulting in larger waves. Large seas with large fetch produce large waves, known as destructive waves. These waves have high heights and short lengths and are characterized as big breakers that have high downward force and strong backwash. They have a high frequency, between 13 and 15 waves per minute.

This downward energy erodes cliffs, and the backwash erodes the shoreline, creating steep shore profiles. Confined storms with high wind speeds form destructive waves and steep depth gradients around headlands. Small seas with small fetch create constructive waves. Constructive waves have low wave height and high frequency with low frequency, between 6 and 8 waves per minute. Constructive waves are associated with weak discharge and strong swash, which develops deep-level shorelines, and are therefore more associated with coastlines of deposition. The size of fetch and type of wave are crucial factors affecting the rate of erosion.

Constructive waves

Coastal Topography 

Swash and Drift Aligned seashores 

The state and direction of the coastline in relation to approaching waves is also an important factor to consider. A section of the coastline may be primarily affected by a large sea fetch, but due to its positioning, it may be protected from destructive waves. In small areas of sea or coastlines that are protected by seaward barriers or islands, prevailing winds do not affect wind direction; thus, waves approaching the coast are parallel to the shore, known as swash-aligned. Swash-aligned shorelines develop large beaches with potential dunes that provide protection from erosion. For coastlines facing vast, open sea, prevailing winds dominate wind direction and waves approach the coast at an angle. These coasts are drift-aligned and associated with the longshore transportation of sediment. These coasts have smaller beaches and may, depending on geology, be more exposed to higher levels of erosion.

Topography – Rock strata 

Concordant and Disconcordant Coastlines 

The topography of a cliff plays a crucial role in determining the rate of erosion. The composition of rock determines the differential rates of erosion, as seen in Swanage, along the Dorset coast. Two headlands, Ballard Point (made of chalk) and Durlston Head (made of limestone) of harder rock types are more resistant to erosion. As a result, they protrude into the ocean, forming headlands. The softer clay of Swanage has eroded much faster to form the cove. Coastlines are called discordant coastlines where the topography alternates between layers (or groups) of hard rock and soft rock. A concordant coastline dominated by limestone (as seen above) has a similar type of rock along its length. Concordant coastlines tend to have fewer bays and headlands. At nearby Lulworth Cove, bays and coves can appear on concordant coasts when weak points in the resistant rock occur. In this case, Portland limestone has been eroded at several points, allowing the underlying sandstone mud to easily erode into a cove.

Concordant coasts, Lulworth Cove 

Headlands and bays do not generally form because of alternating strata. Now and again, along concordant coasts, they occur when a much-jointed area of a precipice, for example, experiences a line of weakness or fault due to exposure.

Lulworth Cove, Dorset, is an example of concordant coasts

Geography – Cliff Profiles and Bedding Planes 

Precipice Profiles and Bedding planes

Bedding Planes 

The shape of the cliff plays a major role in determining the rate of erosion. Sedimentary rocks form as layers of deposited sediment, either on the beds of ancient seas or rivers. Bedding plane layers of sediment represent layers that formed between depositional events. If the bedding planes are flat (A), then the cliff shape will be consistent with a high cliff face.

However, due to tectonic activity, rock can be uplifted and folded. This can alter the arrangement of layers in cliff shapes. Rock that has been uplifted with its bedding planes tilted downwards away from the coast (D) creates a relatively stable cliff shape. Erosion rates will be slowed as deeper layers of rock support the cliff. On the other hand, bedding planes that tilt upwards (C) have a cliff shape that mirrors the angle of the tilt. This is a result of the natural mass movements that occur when the base of the cliff is eroded by wave activity. Other shapes, such as (B), may be more susceptible to erosion. In these cases, the bedding planes are tilted away, causing a gravitational pull on the rock. Additionally, severe joints created by weathering can increase the rate of erosion.

Sub-aerial Processes 

Sub-aerial processes additionally help the pace of erosion of coasts. Sub-aerial processes allude to the processes of weathering and mass movement. Weathering is the separating of rock in situ. It tends to be separated into mechanical and chemical weathering. Mechanical weathering alludes to physical processes like freeze-defrost activity and natural weathering. Freeze-defrost weathering splits up rock as water freezes in breaks. The ice applies pressure and breaks the stone. Natural weathering is brought about by the underlying foundations of vegetation and settling birds. A progressively regular kind of mechanical weathering found at coasts is salt crystallization. This happens as waves store salt crystals in cracks and after some time the salt-like ice applies strain to the cracks. Chemical weathering happens because of a weak chemical reaction between water and rock—e.g. with limestone. Carbonic corrosive, formed from rainwater and carbon dioxide, will react with calcium carbonate in limestone to form calcium bicarbonate. Since calcium bicarbonate is soluble in water, the limestone successfully gets weathered when carbonation happens. The job of weathering is to debilitate precipices—this debilitating hastens the pace of erosion.

Another sub-aerial process is called mass movement. Mass movement alludes to the development of material downslope affected by gravity. They can be quick occasions, for example, avalanches and rockfalls or they can be moderate processes, soil creeps. A typical kind of mass development at coasts is rotational droops. Droops happen because of a mix of components. Marine processes disintegrate and undermine the base of the precipice. This expels the base of the cliff. Likewise, precipitation penetrates the slant through unconsolidated permeable material and afterwards makes a slip plane as it arrives at an impermeable material, for example, clay. The clay and water causes the weighted immersed material above to droop. This process can be found in the chart below. 

Rotational Slump

Rotational slump is a type of mass movement that occurs in coastal environments. It is caused by a combination of marine processes and precipitation. Marine processes such as erosion and wave action weaken and undermine the base of the cliff, removing support and destabilizing the slope. Additionally, precipitation that permeates through the slope can create a slip plane when it reaches an impermeable layer of material such as clay. The added weight of the saturated material, combined with the destabilization of the base, causes the slope to slump or rotate downward. This process can lead to the formation of a curved scar on the cliff face, known as a rotational slump scar, and can contribute to the reshaping of the coastline over time. 

Tides 

Tides are brought about by the gravitational draw of the moon and, to a lesser degree, the sun. Tides are a significant factor in thinking about coastal processes, as their communication with the coastal environment, to a considerable degree, decides the location of numerous coastal landforms. Weak tidal flows and a small tidal range will decide the shape and degree of stream deltas just as the size of seashore profiles. The degree of the tidal range will likewise impact the paces of erosion found at precipices. There are two significant tides to observe; the spring tide and the neap tide. The spring tide occurs twice in a lunar cycle and expands the tidal range by uplifting the elevated tide imprint and bringing down the low tide mark. This is brought about by the arrangement of the moon and sun, which adjusts their gravitational pull. The neap tide delivers a low tidal range, in that the higher tide is lower than usual and the low tide more elevated. This again happens twice in the lunar cycle because of the sun and moon acting against one another. 

Frequently Asked Questions

What are the main processes shaping coastal landscapes?

Coastal processes include erosion, sediment transport, wave action, tides, and the movement of sand and water along the shoreline.

How do waves contribute to coastal erosion and deposition?

Waves erode coastlines through abrasion and hydraulic action, while deposition occurs when wave energy decreases and sediments settle.

How do coastal landforms develop as a result of these processes?

Coastal landforms like cliffs, beaches, spits, and barrier islands form due to interactions between erosion and deposition processes.

What is the significance of littoral drift in coastal systems?

Littoral drift is the movement of sediment along the coast due to wave action. It influences the formation of coastal landforms and impacts erosion and deposition patterns.

How do coastal systems respond to changes in climate and sea level?

Rising sea levels and changing climate patterns can accelerate coastal erosion, alter sediment budgets, and impact the distribution of coastal habitats.

References

  • Coastal Processes. (n.d.). Retrieved from The British Geographer: http://thebritishgeographer.weebly.com/coastal-processes.html
  • Coastal Processes and Beaches. (n.d.). Retrieved from Knowledge Project: https://www.nature.com/scitable/knowledge/library/coastal-processes-and-beaches-26276621/
  • Coastal Systems – Processes of Weathering and Erosion. (n.d.). Retrieved from Tutor2U: https://www.tutor2u.net/geography/reference/coastal-systems-processes-of-weathering-and-erosion
  • Kirwan, J.L. (2019). Coastal geomorphology: An introduction. John Wiley & Sons.
  • Constructive and destructive wave illustration https://www.bbc.co.uk/bitesize/guides/zt6r82p/revision/1
  • Lulworth cove https://en.wikipedia.org/wiki/Lulworth_Cove#/media/File:Lulworth_Cove,_UK_360%C2%B0_Panorama.jpg

Cite/Link to This Article

  • "Coastal Systems and Processes". Geography Revision. Accessed on March 28, 2024. https://geography-revision.co.uk/a-level/physical/coastal-systems-and-processes/.

  • "Coastal Systems and Processes". Geography Revision, https://geography-revision.co.uk/a-level/physical/coastal-systems-and-processes/. Accessed 28 March, 2024.

  • Coastal Systems and Processes. Geography Revision. Retrieved from https://geography-revision.co.uk/a-level/physical/coastal-systems-and-processes/.