Coastal Landforms

Coastal Landforms are formed where the land meets the sea. Both marine and terrestrial processes form a Coastal Landform. Different coastal landforms can be made, either by the land getting smaller or bigger. The kind of rock, how much energy is in the system, and things like waves and tides decide how the coastal area looks. In this article, we will take a look at the meaning of Coastal Landforms, go through its various types, learn about the factors affecting the formation of coastal landforms, and also learn about its interesting features.

Let’s get started!

Definition of Coastal Landforms

Coasts change a lot, sometimes in just a year or even less. Coastal activities are some of the most active geological actions. The way the land and the sea floor look, along with the movement of waves, influences how the coast shapes up. It can either move closer to the sea (emerging) or go back towards the land (submerging).

Formation of Coastal Landforms

Landform	Formation Process
Cliffs and Wave-cut Platforms	Formed by the erosion of rock by waves; wave action at the base of cliffs creates platforms.
Sea Arches and Stacks	Arches form from erosion of headlands by waves; stacks form when arches collapse.
Caves	Created by wave-driven erosion of weaker points in cliffs.
Beaches	Accumulations of sand and pebbles deposited by waves along the shoreline.
Spits and Bars	Spits form from the deposition of sand by longshore drift; bars form when spits connect two headlands, trapping a lagoon.
Dunes	Wind transports and deposits sand from beaches inland, forming mounds or ridges.
Barrier Islands	Long, narrow islands formed from the deposition of sand or sediment parallel to the coast.
Coral Reefs	Form in warm waters from the accumulation of coral skeletons; include fringing reefs, barrier reefs, and atolls.
Atolls	Ring-shaped reefs that form around submerged volcanic islands, with a central lagoon.
Deltas	Form at river mouths from the deposition of sediment as the river slows upon meeting a larger body of water.
Estuaries	Formed by the inundation of river valleys by sea level rise or land subsidence, mixing freshwater with saltwater.
Fjords	Created by deep glacial erosion below sea level; when glaciers retreat, sea water floods the valley, forming deep, narrow inlets.

This table highlights the dynamic interactions between geological processes and the marine environment in shaping the diverse coastal landscapes seen around the world.

Coastal Landforms – Formation of Sea Waves

• Sea waves and tsunamis are the most powerful agents of marine erosion.
• Currents are relatively less impactful means of erosion but are important means of transportation.
• Tides are mainly agents of deposition.

Coastal Landforms – Anatomy of a Sea Waves

Here is the anatomy of a sea wave:

• Crest: The upper part of the wave is called the crest.
• Trough: The lower part of the wave is called the trough.
• Swash: It is the forwarding movement of seawater upon a beach after the ‘breaking of a wave’ Backwash: It is the receding movement of seawater after the ‘breaking of a wave.

Coastal Landforms – Types of Waves

There are two types of waves:

1. Constructive Waves: These waves gently roll over the coasts and help deposition on the coast.
2. Destructive waves: These waves roll over the coast with tremendous force and erode coastal rocks.

Types of Coastal Landform

There are mainly two types of Coastal Landforms i.e. Erosional Coastal Landforms and Depositional Coastal Landforms. Some other Landforms types also include:

1. Delta Landforms
2. Estuary Landforms
3. Lakeshore Landforms
4. Rocky Coast Landforms
5. Sandy Coast Landforms
6. Tropical Coast Landforms

Coastal Landforms Erosional

Coastal Feature	Description	Formation
Chasms	Narrow and deep indents on the coastline.	Formed by alternating bands of hard and soft rocks on the sea-facing side.
Bay	Indents formed as soft rocks are worn away by wave action, leading to chasm widening.	Chasm widens until it becomes a bay.
Capes	Hard rocks left in the sea, forming capes.	–
Sea Cliffs	Steep rocky coasts rising almost vertically above the seawater.	–
Wave-cut Platforms	Flat surface in front of a cliff formed as it gradually retreats due to continuous wave action.	Formed by the retreat of a cliff over time.
Cave	Holes or hollows created at the base of a cliff as sea waves erode softer rocks quickly.	Hollows enlarge over time to form sea caves.
Arch	Formed when two caves on either side of projected rock unite.	–
Stack	Pillar-like structure formed on the coast when the roof of an arch collapses, leaving end sides standing.	–
Stump	Height of a stack is reduced through further erosion, forming a stump.	–
Blow-hole/Gloup	Holes in the cave roof created by continuous sea wave action, known as a blow hole or gloup.	–
Geo	Long, narrow inlet developed as blowholes enlarge, and the cave roof collapses further.	–

Coastal Landforms Depositional

Coastal Feature	Description
Beaches	Deposits of marine sediments like sand, shingles, and cobbles found on the seashore.
Spits and Bars	Spit: Low-lying ridge of sands and pebbles, with one end connected to the mainland and the other ending in the sea.
Hook	A bent spit.
Bars	Ridges of sand parallel to the coast, submerged features.
Tombolo	Bar extension connecting an island to the mainland or linking two islands. Example: Chesil Beach connecting Isle of Portland with the mainland in Dorset, England.
Lagoons	Enclosed seawater area between a bar and the coast. Examples: Chilka Lake on the Odisha coast and Pulicat Lake on the Andhra coast.

Features of Coastal Landforms

Here are some common features of coastal landforms:

1. Headlands and Bays:
   • Headlands are elevated coastal areas that jut out into the sea.
   • Bays are indentations or recesses in the coastline.
2. Cliffs and Sea Stacks:
   • Cliffs are vertical or steep rock faces along the shoreline.
   • Sea stacks are isolated rock columns or pillars that have separated from the mainland due to erosion.
3. Beaches:
   • Sandy shorelines formed by the deposition of sediments brought by waves and currents.
   • Beaches can vary in size, shape, and composition.
4. Spits and Bars:
   • Spits are elongated landforms formed by the deposition of sediments extending from the coast into open water.
   • Bars are similar but may completely cross a bay, lagoon, or estuary.
5. Dunes:
   • Sand dunes are hills or ridges of sand formed by wind or water deposition and vegetation stabilization.
6. Estuaries:
   • Coastal areas where rivers meet the sea, characterized by brackish water due to the mixing of freshwater and seawater.
   • Estuaries often support unique ecosystems.
7. Coves and Inlets:
   • Coves are small, sheltered coastal indentations.
   • Inlets are narrow waterways or passages connecting a bay or lagoon to the open sea.
8. Tidal Flats and Salt Marshes:
   • Tidal flats are areas exposed during low tide, often covered with mud or sand.
   • Salt marshes are coastal wetlands with grasses and other vegetation, influenced by tides.
9. Lagoons:
   • Shallow bodies of water separated from the open sea by barrier islands or spits.
   • Lagoons can be found in coastal areas with extensive sandbars.
10. Sea Caves and Arches:
    • Sea caves are hollowed-out openings in coastal cliffs formed by wave action.
    • Arches are natural arch-like structures carved into rock formations along the coast.
11. Reefs:
    • Submerged or partially submerged structures formed by the accumulation of coral skeletons or other marine organisms.
12. Wave-Cut Platforms:
    • Flat, leveled areas along the coast created by the erosion of rock or sediment by waves.

Factors Affecting the Formation of Coastal Landforms

Waves

Waves at the beach are always moving, and they can be big or small. When waves come closer to the shore, they interact with the ocean floor, picking up sand and making it temporarily float. The bigger the wave, the deeper it can pick up sediment, even large rocks.

Usually, small waves bring sand towards the beach and leave it there. But when there are big waves, especially during storms, they take away sand from the beach and move it to deeper water.

Waves also wear down the rocks along the coast by rubbing against them, kind of like how sandpaper works on a surface. Waves are powerful, and sometimes they can even break up the rocks just by hitting them.

Longshore Currents

When waves come to the shore, they usually don’t hit it straight. They come at an angle, and this makes the waves bend as they enter shallow water. This bending creates a current along the shore, called a longshore current, moving parallel to the coastline.

This current’s speed depends on the size and angle of the waves. On calm days, it might only move about 10–30 centimeters per second, but during storms, it can go over one meter per second. The waves and the longshore current work together to carry a lot of sand and rocks along the shallow water next to the shore.

The direction of the longshore current can go either way along the coast, depending on how the waves approach. The wind is what determines the direction of the waves, and, in turn, the direction of the longshore current.

Even though the current can pick up sediment as it moves, it’s usually the waves that lift the sediment from the bottom. Some places have a lot of sediment moving along the coast, like around 100,000 cubic meters each year, because the wind consistently blows from one direction. Other places might have a more balanced movement of sediment in both directions because the waves come from different directions.

Rip Currents

There’s another type of coastal current caused by waves, often called a rip current (though it’s commonly mislabeled as a rip tide). As waves approach the beach, they push water toward the shore. This causes a small but important increase in the water level near the coast, creating a slight upward slope (setup).

This setup makes the water level at the shoreline a bit higher than farther out where the waves break. This situation is not stable, and to correct it, water moves back toward the sea through the area where the waves break. This movement is usually in narrow pathways and can be quite fast, up to several tens of centimeters per second.

Rip currents are often spaced regularly along the shore and can carry sand and debris. You can often spot them by the plume of suspended sand moving out through the area where the waves are breaking. In some places, these rip currents stick around for months, while in other areas, they might only last for a short time.

Tides

The rise and fall of sea levels caused by the moon’s gravitational pull are regular and can be predicted. This change in water level happens daily or semi-daily, and it varies a lot. Some coasts experience a tidal range of less than half a meter, while others, like the Bay of Fundy in Canada, have tidal ranges over 16 meters.

People classify coasts based on this tidal range into three types: micro-tidal (less than two meters), meso-tidal (two to four meters), and macro-tidal (more than four meters). Most of the world’s coasts fall into the micro-tidal category, but you also find coasts in the other two categories.

Tides play a dual role in shaping coastal features. First, tidal currents, like longshore currents, move a lot of sediment, possibly eroding rocks. Second, the rising and falling tide changes the depth of the water and the position of the shoreline, redistributing the energy of the waves across the shore zone.

Tidal currents transport sediment much like longshore currents but typically only in certain areas, like inlets or estuary mouths, where the coast narrows. Tidal currents along open coasts, like beaches or rocky shores, usually aren’t fast enough to move sediment. The speed of these currents depends on the volume of water passing through, influenced by the tidal range and the area served by the inlet.

FAQs on Coastal Landforms

What is Rock Debris?

Massive rocks that have been destroyed by a melting glacier are left as dispersed remains known as rock debris.

What are Cliffs?

Cliffs are a formation’s highest peak or summit. Cliffs typically develop as a result of the weathering and erosion of the rocks. Natural occurrences like wind or rain that shatter the bits of rock cause weathering. Strong winds and large waves in coastal places separate the softer or grainier rocks from the firmer rocks. Cliffs are the more rigid rocks that are still present.

What is the definition of coastal in geography?

Generally, the land next to rivers and lakes is coastal. But river coasts are called banks and lake coasts are called shores.

What are 4 coastal erosion landforms?

Cliffs, wave cut platforms, headlands, bays, caves, arches and stacks are all coastal landforms formed by erosion.

What are some coastal depositional landform?

Depositional landforms include beaches (sandy and pebble), sand dunes, spits, and bars.