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Coastal Landforms

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Coastal Landforms

Coastlines occur where the land meets the sea and are formed by marine and land-based processes. These processes result in either erosion or deposition, creating different types of coastal landforms. The formation of the coastal landscape depends on many factors, including the type of rock these processes are acting on, how much energy is in the system, sea currents, waves, and tides. When you next visit the coast, look out for these landforms and try to identify them!

Coastal landforms - definition

Coastal landforms are those landforms found along coasts that have been created by coastal processes of erosion and/or deposition. These typically involve some interaction between the marine environment and the terrestrial environment. Coastal landforms differ substantially according to latitude due to differences in climate. For example, landscapes shaped by sea ice are found at high latitudes, and landscapes shaped by coral are found at low latitudes.

How are coastal landforms formed?

Coastal landforms can be formed by erosion, deposition, or both. For example, a beach is a landform where sand or other material deposition is happening, and erosion of sand by the wind and water is also occurring.

Coastlines emerge or submerge from the ocean-based on long-term primary processes such as climate change and plate tectonics. Climate change can involve global warming, where ice caps melt and sea level rises, or global cooling, where ice masses grow, ocean levels shrink, and glaciers press down on the land surface. During global warming cycles, isostatic rebound occurs, meaning that land surfaces 'rebound' as the pressure of continental glaciers is released.

Plate tectonics affects coastlines in many ways. In volcanic 'hotspot' areas of the oceans, new coastlines are formed as new islands arise from the sea or lava flows create and reshape existing mainland coasts. Under the ocean, seafloor spreading adds volume to the ocean as new magma enters the ocean environment, displacing water volume upward and raising the eustatic sea level. Where tectonic plate boundaries are the edges of continents, such as around the Ring of Fire in the Pacific, for example, in California, active coastlines are created where tectonic upheaval and submergence processes often create very steep headlands.

After global warming or cooling stabilises along passive coastlines where tectonic activity is not occurring, the eustatic sea level is reached. Then, secondary processes occur that create secondary coastlines that include many of the landforms described below.

The geology of the parent material is critical in the process of coastal landform creation. The characteristics of rock, including how it is bedded (the angle in relation to the sea), its density, how soft or hard it is, its chemical composition, and other factors, are all important. What lies inland and upstream, which reaches the coast transported by rivers, is a factor for some landforms. In contrast, this could mean the sediment and rock found locally for others. Finally, the contents of the ocean -- local sediment and material transported long distances by currents -- also contribute to landforms.

Mechanisms of erosion and deposition

Ocean currents

An example is a longshore current that moves parallel to the coastline. These currents happen when waves are refracted, meaning they slightly change direction when they hit shallow water. They 'eat' away at the coastline, eroding soft materials such as sand and depositing them elsewhere.

Waves

There are several ways that waves erode material:

  • Hydraulic action - air trapped in the cracks and joints of the cliff face gets compressed when a wave hits the cliff, causing erosion.
  • Abrasion - waves bring bits of rock and sand with them, which grind away the cliff's surface and cause erosion.
  • Attrition - the rocks and pebbles on the shore grind against each other when waves hit them, resulting in the breakdown and rounding of these rocks and pebbles.
  • Solution - some rocks, like chalk or limestone, are easily dissolved by acids contained in the seawater.

Tides

Tides, the rise and fall of sea levels, are regular movements of water that are influenced by gravitational forces from the moon and sun.

There are 3 types of tides:

  1. Micro-tides (less than 2m)
  2. Meso-tides (2-4m)
  3. Macro-tides (more than 4m).

The former 2 help in the formation of landforms by:

  1. Bringing in massive quantities of sediment that will erode the rock bed
  2. Changing the depth of the water, shaping the shoreline

Wind, rain, weathering and mass movement

Wind not only has the capability of eroding material away, but it is also crucial in determining wave direction. This means that wind has both a direct and indirect effect on coastal formation. Wind moves the sand, resulting in beach drift, whereby sand literally migrates toward the prevailing coastal winds.

Rain is also responsible for erosion. Rainfall transports sediments when it runs down to and through the coastal area. This sediment, along with the current from the water flow, erodes anything in its path.

Weathering and mass movement are also known as 'sub-aerial processes.' 'Weathering' means that rocks are eroded or broken down in place. Temperature can affect this as it can influence the state of the rock. Mass movements refer to the movement of material downslope, influenced by gravity. An example is a landslide.

Gravity

As mentioned above, gravity can influence eroding materials away. Gravity is important in coastal processes as it not only has an indirect impact on wind and wave movements but also determines the downslope movement.

Erosional coastal landforms

The erosional landscape is dominated by destructive waves and situated in high-energy environments. A coast formed of more resistant material such as chalk leads to coastal landforms such as arches, stacks, and stumps. A combination of hard and soft materials leads to the formation of bays and headlands.

Examples of erosional coastal landforms

The erosional landscape is dominated by destructive waves and situated in high-energy environments. A coast formed of more resistant material such as chalk leads to coastal landforms such as arches, stacks, and stumps. A combination of hard and soft materials leads to the formation of bays and headlands.

Bays

A bay is a small body of water, set back (recessed) from a large(r) body of water, such as an ocean (figure 1). A bay is surrounded by land on 3 sides, with the 4th side being connected to the large(r) body of water. A bay is formed when the surrounding soft rock, such as sand and clay, is eroded. Soft rock erodes easier and more quickly than hard rock, such as chalk. This will cause sections of land to jut out into the large(r) body of water, called headlands.

Headlands

As mentioned above, headlands can be found around/near bays. Headlands can and do form separately from bays, however. A headland, sometimes also called a 'head', is usually surrounded by water on 3 sides (the opposite of a bay) and protrudes into a large(r) body of water (figure 1). This piece of land is often high, with quite a drop down into the water below. A headland forms when the soft rock surrounding it erodes and the harder rock, which is more resistant to erosion, is left. Characteristics of headlands include high breaking waves and steep cliffs.

The rate of erosion will increase as the headland becomes exposed to more waves and the effects of the wind. When headlands erode, they create distinct features such as caves, arches, stacks, and stumps.

Coastal Landform The bay (yellow) and headlands (red) in San Sebastián, Spain StudySmarterFigure 1: bay (yellow) and headlands (red) in San sebastián, Spain - commons.wikimedia.org

Coves

A cove is a type of bay. However, it is small, circular, or oval and has a narrow entrance (figure 2). A cove is formed by what is called differential erosion, i.e. weathering. The softer rock is weathered and worn away quicker than the harder rock surrounding it. Further erosion then creates the circular/oval-shaped bay with its narrow entrance.

Coastal Landform McWay Cove, California (US) StudySmarterFigure 2: McWay Cove, California, US - commons.wikimedia.org

Peninsulas

A peninsula is a piece of land that, similar to a headland, is almost entirely surrounded by water (figure 3). Peninsulas are connected to the mainland via a 'neck'. Peninsulas can be large enough to hold a community, city, or entire region. However, sometimes peninsulas are small, and you often see lighthouses situated on them. Peninsulas are formed by erosion, similar to headlands.

Coastal Landform Florida, US (yellow), an example of a peninsula StudySmarterFigure 3: Florida, US (yellow) is an example of a peninsula - commons.wikimedia.org

Rocky coast landforms

These are landforms made up of igneous, metamorphic, or sedimentary rock formations. Rocky coastlines are shaped by erosion through marine and land-based processes. Rocky coastlines are areas of high energy where destructive waves make up the majority of erosion.

Caves

Caves can form in headlands. Waves cause cracks to form where the rock is weak, and further erosion leads to caves. (Other caves formations include lava tunnels and glaciers carving out tunnels.)

Arches

When a cave forms on a thin(ner) headland and the erosion continues, it can become a complete opening, with only a bit of landmass at the top. The cave has become an arch (figure 4).

Coastal Landform Arch on Gozo, Malta StudySmarterFigure 4: an arch on Gozo, Malta - commons.wikimedia.org

Stacks

When erosion leads to the collapse of the arch roof, it will create 2 separate pieces of rock:

1. The piece still attached to the mainland2. A separate, stand-alone piece => this is called a stack (figure 5).

Coastal Landform Twelve Apostles, Victoria, Australia StudySmarterFigure 5: Twelve Apostles, Victoria, Australia - commons.wikimedia.org

Stumps

As the stack erodes, it will become a stump. Eventually, the stump wears away below the waterline.

Wave-cut platforms

A wave-cut platform is a flat area in front of a cliff (figure 6). Such a platform is created by, as the name suggests, waves that cut (erode) away from the cliff, leaving behind a platform. The bottom of a cliff often erodes the most quickly, resulting in a wave-cut notch. If a wave-cut notch becomes too large, it can result in cliff collapse.

Coastal Landform Wave-cut platform in Southerndown, South Wales, UK StudySmarterFigure 6: Wave-cut platform in Southerndown, South Wales, UK - commons.wikimedia.org

Cliffs

Cliffs get their shape from weathering and erosion. Some cliffs have a gentle slope because they are made of soft rock, which erodes quickly. Others are steep cliffs because they are made from hard rock, which takes longer to erode.

Depositional coastal landforms

A deposition is when sediment is deposited or laid down. Sediments such as silt and sand settle when the body of water loses its energy, depositing them on a surface. Over time, new landforms are created by this deposition of sediments.

Deposition occurs when:

  • Waves enter an area of lesser depth.
  • Waves hit a sheltered area like a bay.
  • There is a weak wind.
  • The amount of material to be transported is in good quantity.

Examples of depositional coastal landforms

Beaches

Beaches are made up of material that has eroded somewhere else and has then been transported and deposited by the sea/ocean. For this to happen, the energy from the waves has to be limited, which is why beaches are often formed in sheltered areas such as bays.

Sandy beaches are most often found in bays, where the water is more shallow, meaning that the waves have less energy. On the other hand, pebble beaches are most often formed below eroding cliffs. Here, the energy of the waves is much higher.

Spits

Spits are extended stretches of sand or shingle that protrude into the sea from the land (figure 7). This is similar to a headland in a bay. The occurrence of a river mouth or a change in landscape shape leads to the formation of spits. When the landscape changes, a long thin ridge of sediment is deposited, which is the spit.

Coastal Landform Spit at Dungeness National Wildlife Refuge in Washinton D.C. (US) StudySmarter Figure 7: Spit at Dungeness National Wildlife Refuge in Washinton DC (US) - commons.wikimedia.org

Bars and Tombolos

A bar forms when a spit has grown across a bay, joining 2 headlands together. The tombolo is the small isthmus that forms between an offshore island and the mainland (figure 8). Shallow lakes can form behind tombolos and bars, called lagoons. Lagoons are often short-term bodies of water as they can be filled up again with sediments.

Coastal Landform Tombolo near Karystos, Greece StudySmarterFigure 8: Tombolo near Karystos, Greece - commons.wikimedia.org

Saltmarsh

A salt marsh can be formed behind a spit, creating a sheltered area. Due to the shelter, the water movements slow down, which causes more materials and sediments to be deposited. These are found along submergent, meaning party submerged, coastlines, often in estuarine environments.

Coastal Landforms - Key takeaways

  • Geology and the amount of energy in the system affect the coastal landforms that occur along a coastline.
  • Erosional landscapes result from destructive waves in a high-energy coastal environment where the coast is formed of a material such as chalk leading to coastal landforms such as arches, stacks, and stumps.
  • Coastal landforms can be formed by erosion or deposition. In other words, it can either take materials away (erosion) or drop materials (deposition) to create something new.
  • Erosion can happen by sea currents, waves, tides, wind, rain, weathering, mass movement, and gravity.
  • Deposition occurs when waves enter an area of lesser depth, waves hit a sheltered area like a bay, there is a weak wind, or the amount of material to be transported is in good quantity.

Sources:

  • (1) Carys Matthews, Britain’s best coastal caves, arches and stacks, Country File Magazine (2021)

Frequently Asked Questions about Coastal Landforms

Coastal landforms will depend on whether they have been created through erosion or deposition; they range from headland, wave-cut platforms, caves, arches, stacks, and stumps to Offshore bars, barrier bars, tombolos, and cuspate forelands.

Coastlines are formed through marine and land-based processes. The marine processes are the actions of waves, constructive or destructive, and erosion, transportation, and deposition. The land-based processes are a sub-ariel and mass movement.

Geology concerns structure (concordant and discordant coastlines) and type of rocks found at the coastline, soft rocks (clay) are more easily eroded so that the cliffs will be gently sloped. In contrast, hard rocks (chalk and limestone) are more resistant to erosion so that the cliff will be steep.

These are erosion and deposition.

Coastal landforms are formed along the coast. That means that landforms that were not created by coastal processes are not coastal landforms

Final Coastal Landforms Quiz

Question

What are the two main coastal processes that form coastal landforms?

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Answer

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Question

How are bays and headlands formed?

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Answer

Where there is a combination of hard and soft materials

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Question

What is an erosional landscape dominated by?

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Answer

Destructive waves and situated in a high-energy environment

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Question

What are the most common features of coasts?

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Answer

Cliffs, wave-cut notches and platforms

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Question

Over time, cliffs retreat due to..?

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Answer

A combination of sub-aerial weathering and coastal erosion

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Question

How is a wave-cut platform formed?

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Answer

When an unsupported cliff collapses

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Question

What are coastal landforms?

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Answer

Coastal landforms, landforms formed along a coastline, can be anything from mountains or hills to beaches and bays.

Show question

Question

What is a bay?

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Answer

A bay is a small body of water, set back (recessed) from a large(r) body of water, such as an ocean. It is surrounded on 3 sides by land.

Show question

Question

How is a bay formed?


Show answer

Answer

A bay is formed when the surrounding soft rock, such as sand and clay, is eroded. Soft rock erodes easier and more quickly than hard rock, such as chalk. This will cause sections of land to stick out into the large(r) body of water, which are called headlands.

Show question

Question

Describe a headland.

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Answer

A headland, sometimes also called a 'head', is usually surrounded by water on 3 sides (the opposite of a bay) and is sticking out into a large(r) body of water. This piece of land is often high, with quite a drop down into the water below. 

Show question

Question

How are headlands formed and what are some characteristics of headland?


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Answer

A headland forms when the soft rock surrounding it erodes and the harder rock, which is more resistant to erosion, is left. 


Characteristics of headlands include high breaking waves and steep cliffs.

Show question

Question

Which distinct features are created by the erosion of headlands?


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Answer

  • Caves
  • Arches
  • Stacks
  • Stumps

Show question

Question

What is a cove?


Show answer

Answer

A cove is a type of bay, however, it is small, circular or oval and has a narrow entrance.

Show question

Question

How is a cove created?


Show answer

Answer

A cove is formed by what is called differential erosion, i.e. weathering. The softer rock is weathered and worn away quicker than the harder rock that surrounds the softer rock. Further erosion then creates the circular/oval-shaped bay with its narrow entrance. 

Show question

Question

Which 5 ways of erosion are there?


Show answer

Answer

  1. Sea currents
  2. Waves
  3. Tides
  4. Wind, rain, weathering and mass movement
  5. Gravity

Show question

Question

What is a depositional coastal landform and how are they created?


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Answer

A deposition is when sediment is deposited or laid down. Sediments settle down when the body of water loses its energy, depositing the sediments. Over time, new landforms are created by this deposition of sediments.

Show question

Question

Deposition occurs when?


Show answer

Answer

  • Waves enter an area of lesser depth.
  • Waves hit a sheltered area like a bay.
  • There is a weak wind.
  • The amount of material to be transported is in good quantity.

Show question

Question

Name 3 examples of depositional landforms.


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Answer

  1. Beaches
  2. Spits
  3. Bars

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Question

What are the 4 types of erosion by waves?


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Answer

  1. Hydraulic action
  2. Abrasion
  3. Attrition
  4. Solution

Show question

Question

What are the 3 types of tides?


Show answer

Answer

  1. Micro-tides (less than 2m)
  2. Meso-tides (2-4m)
  3. Macro-tides (more than 4m).

Show question

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