Coastal Dynamics and Importance:
- Coastal regions are among the most dynamic zones of the Earth’s surface.
- These areas are subjected to constant change due to the action of:
- Waves
- Tides
- Currents
- Storm surges and tsunamis
- The destructive potential of coastal processes makes their understanding vital for:
- Coastal management
- Hazard mitigation
- Sustainable development
Role of Waves in Coastal Change
- Waves are the primary agents shaping coastal landforms.
- When waves break near the shore:
- They slam water with force against the coast.
- Stir up sediments on the sea bottom.
- Constant wave impact leads to:
- Erosion of coastal rocks and cliffs.
- Redistribution and deposition of sediments.
- Storm waves and tsunami waves:
- Cause sudden, drastic changes.
- Far more destructive than regular wave action.
Influencing Factors in Coastal Landform Formation
Apart from wave energy, landform evolution depends on:
- Configuration of the land and sea floor:
- Steepness, rock type, and structure.
- Nature of the coastline:
- Emerging (advancing) coast: Land extends seaward.
- Submerging (retreating) coast: Land sinks inland.
Two main types of coastlines are explained below assuming sea level is constant.
Types of Coasts
A. High, Rocky Coasts (Submerging Coasts)
Characteristics:
- Coastline appears highly indented with glacially carved valleys (fjords).
- Hill slopes drop sharply into the sea.
- Initially lack depositional landforms.
- Dominated by erosional processes.
Processes and Features:
- Waves crash with high intensity, shaping steep sea cliffs.
- Continuous wave pounding causes cliff retreat, forming wave-cut platforms.
- As cliffs erode, fragments fall, are rounded by wave action, and deposited offshore.
- Over time, these deposits form a wave-built terrace in front of the wave-cut terrace.
- Deposited material helps form:
- Beaches
- Offshore bars
- Barrier bars
- Spits
- Lagoons (when bays are blocked)
B. Low, Sedimentary Coasts (Emerging Coasts)
Characteristics:
- Coastline is smooth and gently sloping.
- Rivers extend their course by building deltas and coastal plains.
- Presence of marshes, swamps, tidal creeks, lagoons.
Processes and Features:
- Waves break gently, stirring bottom sediments.
- Lead to the formation of bars, spits, barrier bars, and lagoons.
- Lagoons evolve into swamps, which later turn into coastal plains.
- Steady sediment supply is crucial for maintaining depositional features.
- Storms and tsunamis may disrupt and reshape these features dramatically.
- Large rivers contribute to delta formation (e.g., Ganga, Mahanadi).
Indian Context
West Coast of India:
-
- High, rocky, retreating coast
- Dominated by erosional features
East Coast of India:
-
- Low, sedimentary, advancing coast
- Dominated by depositional features
Erosional Landforms by Waves
a) Sea Cliffs
- Steep rock faces formed as waves erode the base of headlands.
- Can be a few metres to 30 metres or more in height.
- Created by the undercutting action of waves.
- May be backed by rock debris fallen from above.
b) Wave-Cut Terraces
- Flat or gently sloping platforms at the base of sea cliffs.
- Formed by continuous erosion and cliff retreat.
- Covered by rock debris.
- Occur above the average wave height.
c) Sea Caves
- Hollows formed at the cliff base by wave erosion.
- Widen and deepen over time.
- Caused by wave force and smashing debris.
d) Sea Stacks
- Isolated rock columns in the sea, remnants of receded cliffs.
- Originally part of the cliff/hill.
- Temporary features — eventually worn down by waves.
Depositional Coastal Landforms
a) Beaches
- Accumulations of sediments (sand, gravel, pebbles) along the shore.
- Mainly formed by:
- Sediments brought by rivers
- Material eroded from cliffs
- Dynamic features — may vary in size and composition by season.
- Types:
- Sandy Beaches
- Shingle Beaches (contain small pebbles or cobbles)
b) Sand Dunes
- Formed behind beaches by windblown sands.
- Appear as long ridges parallel to the coastline.
- More common on low sedimentary coasts.
c) Offshore Bars
- Ridges of sand/shingle in the offshore zone, parallel to the shoreline.
- Submerged features, may emerge during low tide.
d) Barrier Bars
- Exposed offshore bars formed by accumulation of sand/shingle.
- Can block river mouths or bay entrances.
e) Spits
- Elongated ridges of sand/shingle attached to the coast at one end.
- Formed by longshore drift.
- May extend into bays or be attached to headlands.
f) Lagoons
- Shallow water bodies between coast and barrier bars/spits.
- Created when spits or barrier bars block bay mouths.
- Over time, get filled with sediments from:
- Rivers
- Wind-aided beach deposits
- Eventually become swamps, then coastal plains.
Differences Between High Rocky and Low Sedimentary Coasts
| Feature | High Rocky Coast | Low Sedimentary Coast |
| Terrain | Steep, irregular | Gentle, smooth |
| Coast Type | Submerging | Emerging |
| Dominant Process | Erosion | Deposition |
| Landforms | Cliffs, wave-cut terraces, caves, stacks | Beaches, dunes, bars, spits, lagoons |
| Appearance | Indented coastline | Extended coastline |
| Examples in India | West coast | East coast |