What are Coastal Landforms?
Coastal landforms are the landforms along the coastline that are mostly formed by erosion and sediments from waves, longshore currents, rip currents, tides, and climatic factors like wind and rainfall, and temperature include headlands, cliffs, bays, spits, salt marshes, and beaches.
Formation of Coastal Landforms
- Abrasion – waves carry material which thrashes against the cliff and progressively disintegrate it.
- Hydraulic action – waves while approaching the coast trap air and push it into breaks of the cliff. This eventually makes the rock weak.
- Corrosion – the rock salts gradually get corroded by acids in seawater over thousands of years. This is also known as a solution.
- Attrition – waves make the rocks to smash against each other, which breaks them down into smaller and rounded parts.
The longshore currents are created when waves are refracted while entering into shallow water. These longshore currents carry along with themselves vast quantities of material and sediments. Another type of current that contributes towards the formation of coastline landforms is rip current. It is formed when the water rises along a slight but important slope due to some net shoreward transport of water when the waves move towards the beach.
Tides are the regular movement of seawater due to astronomical conditions. Coasts have been classified depending on the type of tides formed them. They are micro-tidal (less than two meters), meso-tidal (two to four meters), and macro-tidal (more than four meters).
Tides play two types of role in the formation of landforms. First, tidal currents transport massive quantities of sediments and even erode the rock bed. Second, the tides help shape the shoreline by changing the depth of water along with it.
Wind, Rain, and Weathering
There is also erosion by wind, weathering, sub-aerial processes, and mass movement. Wind acts both as an element that erodes the rocks and a force that determines the direction of the waves. The seasonal pattern of the winds gets directly translated into different kinds of sea currents that are, in turn, responsible for diversity in the coastal landforms. Thus, the wind has a direct and indirect effect on the formation of coastal landforms. Coastal dunes are primarily the result of direct impacts of onshore wind movements.
Forces like rainfall and temperature are other factors behind the formation of coastal landforms. Rainfall is responsible for transportation of sediment to the coast through the runoff in the form of streams. But temperature impacts in a different way. It causes physical weathering of the rocks in warm regions and fragments in the rock in the cold areas when water freezes inside the holes of the rock and expand to create a crack in it and thereby yield sediments.
Gravity has a significant role to play in coastal processes. Besides having an indirect impact on wind and wave movements, gravity directly determines the downslope movement of sediment and rock. The outcome of this downward movement is apparent along shoreline cliffs where the sea currents hit the base of the cliffs and the dented slope to cause an ultimate collapse of the rock in the seawater. The detached rock can also get accumulated at the base of the cliff as debris.
Different Types of Coastal Landforms
Broadly, the coastal landforms can be divided into two groups, those formed due to erosion and those formed due to deposition.
The coastal landforms resulting out of erosion include
- Headlands and bays
- Caves, stacks, arches, and stumps
- Wave-cut platforms
The coastal landforms resulting out of deposition include
Other coastal landforms are
- Delta landforms
- Estuary landforms
- Lakeshore landforms
- Rocky coast landforms
- Sandy coast landforms
- Tropical coast landforms
Headlands and Bays
When there are different types of rock along a coastline, the weaker or softer rock, like clay, erode fastest leaving more resistant rock types such as granite, sticking out to create headlands. Bays, on the other hand, are created from less resistant rocks.
Caves, Stacks, Arches, and Stumps
Headlands are highly vulnerable to further erosion by water and wind and other features such as caves, stacks, arches, and stumps may emanate from them.
Waves usually hit the bottom of the cliff hard during storms and at high tide. The weathering weakens the uppermost part of the cliff, which subsequently falls off in the sea. The process continues till a rocky platform at the base gets formed. This is called the wave-cut platform.
Spits are created through a process called longshore drift, which moves the material along the coastline. Spurn Head at the north of the Humber Estuary in the northeast of England is an example of spit.
Behind the spit, salt marshes are formed. The area behind a spit is usually a sheltered area where water movement is slow and hence more material gather there as deposits. Deposition leads to the formation of a salt marsh.
Deposits of sediment are the leading cause behind the formation of beaches.
The river mouths are often deposited with an excess supply of sediments and form a triangular shape landscape like the Greek capital letter delta (Δ). The Mississippi River delta is one such good example.
The word “estuary” is a derivation from the Latin word “aestuarium,” meaning tidal. A natural estuary is a landform that is semi-enclosed, extended coastal basin receiving an inflow of freshwater as well as saltwater. These are short-lived and usually, get ruined quickly by rapid sedimentation.
Small landforms created by the waves and sediments from lakes are termed lakeshore landforms. These are also temporary landforms that quickly gets filled with sediments.
Rocky Coast Landforms
Resulting primarily from erosion, the rocky coasts are typically situated at active boundaries with slender continental shelves. These coasts are composed of different types of rocks, namely igneous, sedimentary, or metamorphic and are filled with complex tectonic landforms like folds, faults, and igneous intrusions and extrusions. Kenai Fjords National Park in Alaska is a perfect example of rocky coasts.
Sandy Coast Landforms
The sandy coast landforms, mostly located in the passive margins, have extremely dynamic environments that are subject to rapid and severe changes. The primary characteristics of this landform are low-wave energy, strong offshore sediment influence, and a full continental shelf. The beaches are generally dominated by waves. Barrier islands, barrier spits, beaches, tombolos, and dunes are typical features of the sandy coast landforms.
Cape Cod National Seashore in Massachusetts and Cumberland Island National Seashore in Georgia are notable examples of sandy coast landforms.
The coasts constitute one of the most dynamic environments on the earth. They signify the transition zone between land and marine ecosystems that are incredibly vulnerable regions. These areas are often subjected to changes in environmental forces such as cyclones, tsunami, earthquakes, and climate changes. They also host a wide variety of flora and fauna, which are significant for the sustenance of the local ecosystem.
The in-situ beauty of the coastal landforms is a major attraction for people and thereby creates tourism opportunities for their country of residence. However, they should be protected from excessive human exploitation. The ecological balance of these landforms is crucial for retaining the equilibrium both in terrestrial and marine life. Hence, they need more considerable restoration and preservation.