Landform
A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body. The terrain landscape formed due to the landform is topography. The characteristic physical attributes like slope, stratification, elevation, orientation, rock exposure, and soil type categorize landforms. Landform includes hills, mounds, ridges, berms, cliffs, rivers, valleys, volcanoes, peninsulas, and various other structures. Minor landforms include canyons, valleys, basins, and buttes, whereas major landforms are hills, mountains, plateaux, and plains.
Coastal Landforms Definition
Coastal landforms mean any of the relief features remaining on the coast because of the combination of processes, sediments, and the geology of the coast itself. The development and persistence of landforms are the results of a combination of processes acting on sediments and rocks present on the coast. The power and current of waves play a major role in these processes.
Beach, delta, coastal dune, wave-cut platform, a sea stack, sea cliff, and sea arch are some of the famous coastal landforms.
Erosional and Depositional Landforms
There are two major types of coastal landforms - erosion and deposition. The erosional and depositional landforms, though they contain some similar features, show distinct different types of landforms. Erosional landforms show high relief and rugged topography. They can be seen on the leading edge of lithospheric plates, the west coasts of North and South America. The erosional coasts also occur due to glacial activity, which is seen in New England and the Scandinavian countries.
The erosional features are dominated by exposed bedrocks with steep slopes and high elevations near the shore. The bedrocks resist the erosion leading to its slow rate of shoreline retreat. The type of rocks and their lithification play a major role in the rate of erosion.
Features of Sea Erosion
Seacliff Formation
The sea bedrock cliffs range from a few meters to hundreds of meters above sea level. The sea cliff landforms are the most widespread of erosion coasts. The wave-induced erosion near sea level and collapse of rocks at higher elevation lead to vertical nature. One can observe a notch in cliffs when they are extended to the shoreline where waves batter the bedrock.
At the base of the sea cliffs, one can find many veneers of sediment that form a beach. The sediment might be of sand, but it is more of cobbles or boulders, a coarse material. These types of beaches might get demolished with the strong waves during the stormy seasons as they are made in low wave-energy conditions. Some beaches of California and Oregon are its example.
Coastal erosion means breaking down and carrying away materials by the sea, and deposition means the material carried away by sea is deposited or left behind on the coast. Coastal erosion happens due to ‘destructive waves’. We know that in the stormy season, the waves are very powerful and can destroy material into pieces. The strong backwash of waves pulls the material away in the sea.
Destructive Waves
Erodes through four main processes as -
Hydraulic Action
It is a force against the coastline that leads to dislodging and carrying the material away by the sea.
Compression
This can be seen in rocky areas when the water burst against the crack of rocks. These cracks keep on spreading as the air gets compressed and decompressed because of the waves crashes. The creation of caves is the result of compression as the rocks go on breaking off.
Abrasion
Abrasion means when the material is thrown to the coast with the swashes, they tend to break and spread, and this leads to more material backwashing into the sea.
Attrition
Attrition means the crashing of rocks and stones against each other while they are carried away by the sea. The attrition gives result formation of sand and rounded pebbles on the beach.
Sea Caves
When the cracks in the rock at the base are eroded and expanded by the continuous crashing of waves, the sea caves are formed. It is the result of constant compression and hydraulic action.
Sea Arch
Sea arch is formed when the headland is broken through while waves continue to erode and expand to cut through.
Sea Stack
Sea stack means the sea arch is no more capable of supporting till the root and falls broken in the sea. The remaining pillar-like rock is called a sea stack.
Sea Stump
The sea stump means a broken pillar is remaining just above sea level. It is a sea stuck almost completely eroded.
Constructive Waves
Are of low energy and high swashes. Swashes mean the waves deposit or drop the material on the coast. They have stronger swashes than backwashes. This leads to a build-up of material washed away during backwashes. This results in the formation of beaches.
FAQs on Landforms of Erosional Coasts
1. What are the main landforms created by coastal erosion?
Coastal erosion carves out several distinct features from the coastline. The most common erosional landforms include:
- Sea Cliffs: Steep rock faces that form along the coast where the sea erodes the land.
- Sea Caves: Hollows formed by wave action at the base of a cliff.
- Sea Arches: Natural arches that form when a sea cave erodes through a headland.
- Sea Stacks: Tall columns of rock that are left isolated in the sea after a sea arch collapses.
- Wave-Cut Platforms: Flat, rocky areas at the base of a cliff, visible at low tide, showing where the cliff has retreated.
2. How exactly does wave action shape these erosional landforms?
Waves shape coastal landforms primarily through four key processes:
- Hydraulic Action: The sheer force of the water crashing against the coastline traps air in cracks, compressing it and causing the rock to break apart.
- Abrasion (or Corrasion): Rocks and sediment carried by the waves are hurled against the cliff face, acting like sandpaper to wear it away.
- Attrition: Rock fragments carried by the sea knock against each other, becoming smaller, smoother, and more rounded.
- Solution (or Corrosion): Certain types of rock, like chalk and limestone, are dissolved by the slightly acidic seawater.
3. What is the difference between erosional and depositional coastal landforms?
The main difference lies in whether land is being removed or added. Erosional landforms, like sea cliffs and stacks, are created by the sea wearing away and removing rock and sediment from the coastline. In contrast, depositional landforms, like beaches and spits, are created when the sea loses energy and drops the sediment it was carrying.
4. Why do some parts of a coastline have cliffs and caves, while others have sandy beaches?
This happens due to a process called differential erosion. Coastlines are often made of alternating bands of hard rock (like granite) and soft rock (like clay). The sea erodes the softer rock much faster, creating sheltered bays where sand can accumulate to form beaches. The more resistant hard rock is eroded much slower and juts out into the sea, forming headlands where erosional features like cliffs and caves are concentrated.
5. How does a sea cave eventually become a sea stack?
This is a natural progression that happens over a long time. First, waves attack a weakness at the base of a headland, forming a sea cave. As erosion continues, the cave may break through to the other side of the headland, creating a sea arch. Over time, the top of the arch is weakened by weathering and eventually collapses, leaving a tall, isolated pillar of rock known as a sea stack.
6. Are sea cliffs permanent features of a coastline?
No, sea cliffs are not permanent. They are constantly changing and retreating inland. Waves continuously attack the base of the cliff, a process called undercutting. This creates a wave-cut notch. Eventually, the overhanging rock becomes unstable and collapses. This process repeats, causing the cliff to retreat and leaving behind a flat, rocky surface called a wave-cut platform.
