Coastal Erosional Landforms: Cliffs, Terraces, Caves, Stacks
Geography › Geomorphic Processes and Landform Evolution · Topic 3.25
Waves erode the coast by hydraulic action (the force of water and compressed air in cracks), abrasion (the grinding by sand and pebbles), attrition and solution. Where waves attack rock, they produce erosional landforms: sea cliffs and wave-cut platforms (terraces), notches, caves, arches, stacks and stumps. These forms develop in a sequence as cliffs retreat, and are best seen on rocky, high-energy coasts, such as the Konkan coast, and on chalk coasts like those of southern England.
6 min read · UPSC Prelims · Geography · Geomorphic Processes and Landform Evolution
At a Glance
- Processes Hydraulic action, abrasion, attrition, solution
- Cliff Steep rock face cut by waves
- Platform Rock terrace at the foot of a cliff
- Sequence Cave, arch, stack, stump
- Best developed Rocky, high-energy coasts
- Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution
Where Does It Fit?
This topic begins the pair on coastal landforms, after those of glaciers. It takes the erosional work of waves, while the next topic covers deposition, and the macro on oceanography later covers waves themselves. Previous topic: Glacial Depositional Landforms: Glacial Till, Moraines, Eskers, Outwash Plains, Drumlins. Next topic: Coastal Depositional Landforms: Beaches, Dunes, Bars, Barriers, Spits.
How Do Waves Shape Coasts?
In short: waves cut back rocky coasts and build up sandy ones.
The coast is the zone where land and sea meet, and the features shaped there are called marine landforms. Waves, driven by wind, are the main agent of change, along with tides and currents. Waves erode by hydraulic action, in which the force of water and compressed air in cracks breaks rock, by abrasion, in which rocks and sand carried by the waves scrape the cliff, by attrition, in which carried pebbles wear each other down, and by solution of soluble rock. Waves are of two kinds. Destructive waves are high and steep, with a strong backwash, and they erode the beach. Constructive waves are low and long, with a strong swash, and they build up the beach. The behaviour of the sea is discussed in Ocean Currents: Horizontal and Vertical Motion; Cold and Warm Currents and Tides: Tidal Currents, Types and Importance.
How Do Cliffs, Platforms, Caves, Arches and Stacks Form?
- Notch and cliff: waves undercut the base of a rock face at high tide level, cutting a notch. When the overhang falls, the cliff retreats.
- Wave-cut platform: as the cliff retreats, a gently sloping rock shelf is left at its foot, exposed at low tide. If uplifted, it becomes a marine terrace.
- Cave: waves force their way into cracks and weak spots in a headland, and widen them into sea caves.
- Arch: when two caves from opposite sides meet, or a cave goes through the headland, an arch is formed.
- Stack: the arch roof collapses, leaving a detached pillar of rock in the sea.
- Stump: the stack is eroded to a low rock outcrop visible at low tide.
The best known examples include the Twelve Apostles in Australia, Old Harry Rocks and Durdle Door in England, and the stacks at Vagator in Goa and along the Konkan coast of India.
What Are the Erosional Landforms of Coasts?
- Sea cliffs: steep rock faces cut back by wave action at their base; they retreat inland.
- Wave-cut notch and platform: a notch is cut at the base of the cliff and, as the cliff collapses and retreats, a gently sloping rock surface, the wave-cut platform, is left at the foot.
- Headlands and bays: where hard and soft rocks alternate along the coast, soft rock erodes into bays and the hard rock stands out as headlands.
- Sea caves, arches, stacks and stumps: waves enlarge cracks into caves; if a cave cuts through a headland it forms an arch; when the arch roof falls, a detached rock pillar, a sea stack, is left, and it is eroded down to a stump. The Twelve Apostles of Victoria, Australia, are well-known stacks.
- Blowholes: vertical shafts in sea caves through which spray is forced out.
The white cliffs of Dover in England are made of chalk, a sedimentary rock described in Sedimentary Rocks.
What Controls the Rate of Coastal Erosion?
| Factor | Effect |
|---|---|
| Wave energy | Large waves, long fetch and storms increase erosion |
| Rock type | Hard granite resists; soft clay, sand and chalk erode quickly |
| Rock structure | Joints and faults let waves in; rock dipping seaward is unstable |
| Sea level | Rising sea level moves the attack higher on the shore |
| Sediment supply | Beaches protect the coast; their loss exposes cliffs |
| Human activity | Sand mining, dams that trap river sand, and ports change the balance |
How Serious Is Coastal Erosion in India?
Assessments by the National Centre for Coastal Research, which covered about 6,900 km of the Indian coastline for 1990 to 2018, found that roughly one-third, about 33.6 per cent, of the coast was eroding, about 27 per cent was accreting and about 40 per cent was stable. Causes include rising sea level, stronger storms, sand mining, dams that reduce sediment supply, and building on the shore. Protection includes sea walls, groynes, artificial beach nourishment, restoration of mangroves, shelterbelts and the Coastal Regulation Zone rules, which restrict construction near the shore. As an analytical point, hard structures such as sea walls often shift erosion to neighbouring beaches, which is why shoreline management plans increasingly favour natural buffers such as mangroves and dunes.
How Are Coasts Protected?
Hard methods include sea walls, groynes and rock armour, which hold the coast in place but often shift erosion down the coast. Soft methods include beach nourishment with sand, planting mangroves and dune vegetation, and moving buildings back from the sea. India’s Coastal Regulation Zone rules also limit construction near the shore. The sediment carried along the coast is moved and laid down as described in Coastal Depositional Landforms: Beaches, Dunes, Bars, Barriers, Spits. The ocean waves behind it all are in Waves: Wavelength, Amplitude, Frequency.
Why Is This Topic Important?
- Sequence Cave to stump is asked
- India Erosion on coasts
- Policy Coastal protection
What Came Next?
The next topic describes the depositional landforms of the coast: beaches, dunes, bars and spits. Next topic: Coastal Depositional Landforms: Beaches, Dunes, Bars, Barriers, Spits.
Key People and Terms
- Hydraulic action Force of water in cracks
- Wave-cut platform Rock shelf at the foot of a cliff
- Sea arch Rock opening through a headland
- Stack Detached rock pillar
- Stump Low remnant of a stack
- Groyne Barrier built across a beach
Exam Corner
Points to Remember
- Sequence: cave, arch, stack, stump.
- A wave-cut platform lies at the foot of a cliff.
- Erosion is strongest on rocky, exposed coasts.
- Hard defences can shift erosion down the coast.
- The Coastal Regulation Zone limits building near the shore.
Do Not Confuse With
- Stack and stump Tall pillar versus low remnant
- Arch and cave Opening through versus a dead-end hollow
- Hydraulic action and abrasion Force of water versus grinding by load
Memory Hook
Notch to cave, cave to arch, arch to stack, stack to stump.
Mains Angle
Questions ask for the sequence and for coastal erosion in India. These points add depth.
- Sequence Cliff retreat
- Causes Waves, rock, people
- Management Soft and hard measures
A Question You May Face
An original practice question, not a past paper question.
“Explain how sea cliffs, caves, arches and stacks are formed and discuss the problem of coastal erosion in India.”
How to Answer
- Processes Hydraulic action and abrasion.
- Sequence Cave to stump.
- India Keralam (Kerala), Odisha, Tamil Nadu.
- Response Soft and hard methods.
GS Relevance
Frequently Asked Questions
What are the erosional landforms of the coast?
Coastal erosional landforms include sea cliffs, wave-cut notches and platforms, headlands and bays, sea caves, arches, stacks and stumps, and blowholes. They are formed by hydraulic action, abrasion and attrition by waves, and develop best on rocky and exposed coasts.
How is a sea stack formed?
Waves enlarge cracks in a headland into a cave, and the cave may break through to form an arch. When the roof of the arch collapses, an isolated rock pillar, a sea stack, is left standing, and it is later worn down to a stump.
What is a wave-cut platform?
A wave-cut platform is a gently sloping rock shelf at the foot of a sea cliff, formed as waves undercut the cliff and it retreats. It is often exposed at low tide. If the land is uplifted or the sea level falls, the platform is left above the sea as a marine terrace.
What causes coastal erosion?
Coastal erosion is caused by waves, tides and currents, especially during storms, and is made worse by rising sea level, loss of mangroves and beaches, sand mining, and structures such as ports and dams that cut off the sand supply. Weak rocks erode faster than hard rocks.
What is hydraulic action?
Hydraulic action is the erosion by the sheer force of water. Waves force water and compressed air into cracks in rocks, and when the wave retreats, the sudden release of pressure widens the cracks and loosens the rock. It is one of the main ways that waves erode cliffs.
PYQ Practice — Statement Analysis
1 A sea stack is left when the roof of a sea arch collapses.
It is later reduced to a stump.
2 A sea stack is left when the roof of a sea arch collapses.
It is a detached rock pillar.
3 Wave-cut platforms lie at the top of a sea cliff.
They lie at the foot.
4 Mangroves help to protect coasts from erosion.
Their roots hold sediment and absorb wave energy.
Past Mains Questions on This Topic
This topic comes under Geomorphic Processes and Landform Evolution. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
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