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Coastal Landforms

Coastal Landforms

Coastlines occur where the land meets the sea and they 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, deposition, or both. 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.

Types of Coastal Landforms

There are two main types of coastal landforms- erosional coastal landforms and depositional coastal landforms. Let's take a look at how they are formed!

How are coastal landforms formed?

Coastlines emerge or subside from the ocean through 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.

Isostatic rebound: Process whereby land surfaces rise or 'rebound' from lower levels after ice sheets melt. The reason is that ice sheets exert massive force on the land, pushing it downward. When ice is removed, land rises, and sea level drops.

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 (its angle in relation to the sea), its density, how soft or hard it is, its chemical composition, and other factors, are all important. What type of rock lies inland and upstream, reaching the coast transported by rivers, is a factor for some coastal landforms.

In addition, the contents of the ocean -- local sediment as well as material transported long distances by currents -- contribute to coastal 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:

  • Abrasion. From the verb 'to abrade,' meaning to wear down. In this case, the sand that the wave is carrying wears away at solid rock, like sandpaper.
  • Attrition. This is often confused with abrasion. The difference is that with attrition, particles hit eat other and break apart.
  • Hydraulic action. This is the classic 'wave action' whereby the force of water itself, as it smashes against the coast, breaks rock apart.
  • Solution. Chemical weathering. Chemicals in the water dissolve certain types of coastal rocks.

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 erode the rock bed.
  2. Changing the depth of the water, shaping the shoreline.

Wind, rain, weathering and mass movement

Wind not only can erode material but also is 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 the erosion of materials. Gravity is important in coastal processes because 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 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

Below is a selection of the most common coastal landforms that you might encounter in the UK.

Bays

A bay is a small body of water, recessed (set back) from a large(r) body of water such as an ocean (figure 1). A bay is surrounded by land on three sides, with the fourth side 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

Headlands can be found near bays (figure 1). Headlands can and do form separately from bays, however. A headland, sometimes also called a 'head', is usually surrounded by water on three sides and protrudes into a body of water. 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 landforms figure 1 headland and bay in Western Australia StudySmarterFigure 1: headland and bay in Western Australia. Hughesdarren, Public Domain Wikimedia Commons

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. The softer rock is weathered and worn away quicker than the harder rock surrounding it. Further erosion then creates the circular or oval-shaped bay with its narrow entrance.

Coastal landforms figure 2 Lulworth Cove England StudySmarterFigure 2: Lulworth Cove in Dorset, England. Adrian Pingstone, Public Domain Wikimedia Commons

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 landforms figure 3 Monterey Peninsula California StudySmarterFigure 3: Monterey Peninsula, California. Mertbiol, CC-0 Wikimedia Commons

Rocky coast landform

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 cave formations include lava tunnels and glacially carved tunnels.

Arches

When a cave forms on a narrow headland and erosion continues, it can become a complete opening, with only a natural bridge of rock at the top. The cave then becomes an arch (figure 4).

Coastal Landforms Figure 4 arch on Gozo, Malta StudySmarterFigure 4: an arch on Gozo, Malta. Berit Watkin, CC-BY-2.0 Wikimedia Commons

Stacks

Where erosion leads to the collapse of the arch's bridge, separate pieces of free-standing rock are left. These are called stacks (figure 5).

Coastal Landform Twelve Apostles, Victoria, Australia StudySmarterFigure 5: Twelve Apostles, Victoria, Australia. Jan, CC-BY-2.0 Wikimedia Commons

Stumps

As the stacks erode, they become stumps. Eventually, stumps wear 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. Yummifruitbat, CC-BY-2.5 Wikimedia Commons

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

Deposition refers to the laying down of sediment. Sediments such as silt and sand settle when a 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, Washington state, US. USFWS-Pacific Region, CC-BY-2.0 Wikimedia Commons

Bars and Tombolos

A bar forms where 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 called lagoons can form behind tombolos and bars. Lagoons are often short-term bodies of water as they can be filled up again with sediments.

Coastal landforms tombolo Shetland StudySmarterFigure 8: tombolo connecting St. Ninian's island to Mainland, Shetland, UK. ThoWi, Public Domain, Wikimedia Commons

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.

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.

The two main coastal processes that form coastal landforms 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.

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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.

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Question

How is a bay formed?


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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.

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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. 

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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.

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Question

Which distinct features are created by the erosion of headlands?


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Answer

  • Caves
  • Arches
  • Stacks
  • Stumps

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Question

What is a cove?


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Answer

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

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Question

How is a cove created?


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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. 

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Question

Which 5 ways of erosion are there?


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Answer

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

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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.

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Question

Deposition occurs when?


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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.

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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

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Question

What are the 3 types of tides?


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Answer

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

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