Coastal landforms are the various shapes and features that appear along the edges of continents and islands. They’re the result of complex interactions between the land, sea, and atmosphere over long periods of time.
These landforms are constantly changing due to the action of waves, tides, and currents, as well as erosion, deposition, and tectonic activity.
Action of Waves, Tides, and Currents
- Waves: Created by wind blowing over the sea surface, they are the primary force behind most coastal changes. The energy from waves shapes both erosional and depositional landforms.
- Tides: The regular rise and fall of sea levels caused by the gravitational pull of the moon and sun. Tides influence how far wave action reaches inland and help in sediment movement.
- Currents: These are the continuous movements of seawater, often generated by wind and differences in water density. Coastal currents play a major role in transporting sediments along shorelines (longshore drift).
Mechanism of Marine Erosion
Marine erosion is how the sea wears away the coast. The major processes involved are:
- Hydraulic action: The sheer force of waves compressing air into cracks in the rock, eventually breaking it apart.
- Abrasion (corrasion): Pebbles and sand carried by waves grind against the shoreline like sandpaper.
- Attrition: Rocks and pebbles carried by waves collide with each other, breaking into smaller, smoother pieces.
- Solution (corrosion): Seawater, especially when slightly acidic, can dissolve rocks like limestone and chalk.
These processes constantly reshape coastal landscapes.
Coastal Features of Erosion
1. Capes and Bays
When a coastline has alternating hard and soft rock, the softer rock is eroded faster, forming bays (inlets), while the harder rock remains, forming capes (headlands).
- Example: The coastline of Konkan, Maharashtra shows such headlands and bays.
2. Cliffs and Wave-Cut Platforms
When waves continuously pound against steep coasts, they erode the base of rocks, causing the upper parts to collapse and form cliffs. The base becomes flat, forming a wave-cut platform.
- Example: The chalk cliffs of Dover in England.
3. Caves, Arches, Stacks, and Stumps
- Cave: Formed when waves erode a weak spot in a cliff.
- Arch: If the cave is eroded all the way through, it becomes an arch.
- Stack: When the roof of an arch collapses, a pillar-like stack remains.
- Stump: Over time, the stack is worn down to a small stump.
- Example: Old Harry Rocks, Dorset Coast, UK.
Coastal Features of Deposition
Deposition occurs when wave energy decreases, and materials like sand and pebbles are dropped along the shore.
1. Beaches
Formed from accumulated sand and gravel. They are dynamic, often changing with seasons and storm events.
- Example: Marina Beach, Chennai.
2. Spits and Bars
- Spit: A long, narrow stretch of sand extending from the land into the sea, often curved at the end.
- Bar: If a spit connects two headlands across a bay, it forms a bar.
- Example: Spurn Head, UK (spit); Chilika Lake Bar, Odisha (India).
3. Marine Dunes and Dune Belts
When strong onshore winds pick up dry beach sand and deposit it inland, sand dunes are formed. Over time, these form dune belts.
- Example: Coastal dunes in Goa and Rann of Kutch (India).
Types of Coasts
1. Coastlines of Submergence
These coasts were once land but are now underwater due to rising sea levels or land sinking.
(a) Fjord Coasts
Formed when deep glacial valleys are flooded by the sea. They have steep, cliff-like sides.
- Example: Norwegian coast, New Zealand’s South Island.
(b) Dalmatian Coasts
Long, narrow islands and parallel inlets formed by submergence of folded mountains running parallel to the coast.
- Example: Dalmatian Coast, Croatia.
(c) Estuarine Coasts
When river mouths are drowned, forming wide, funnel-shaped estuaries.
- Example: Hooghly Estuary, West Bengal; Thames Estuary, UK.
2. Coasts of Emergence
These coasts are formed due to falling sea levels or land uplift (due to tectonics or isostatic rebound).
(a) Uplifted Lowland Coasts
Flat coastal plains emerge from the sea, exposing former sea beds. These are often marshy and rich in sediments.
- Example: Eastern coastal plains of India, especially Tamil Nadu and Andhra Pradesh.
(b) Emergent Upland Coasts
Hilly or mountainous land is raised above sea level, leaving behind raised beaches and cliffs.
- Example: Parts of the Scottish coast, and some areas along the Konkan coast, India.
