Coastal Landforms

Notes

Coastal landforms are shaped by waves, tides and currents. Constructive waves (low, spilling) build beaches; destructive waves (high, plunging) erode. Longshore drift moves sand along the coast.

Erosional landforms (hydraulic action, abrasion, attrition, corrosion)

Sea cliffs and wave-cut platforms; wave-cut notches.
On headlands: sea caves, arches, stacks and stumps (in sequence); blowholes.

Depositional landforms

Beaches, spits (sand ridges attached at one end to the land), bars and barrier islands.
Lagoons (water enclosed behind a bar): Chilika (the largest brackish-water lagoon in Asia, Odisha), Pulicat (Andhra Pradesh and Tamil Nadu), Vembanad (Kerala backwaters).
Tombolo: a bar linking an island to the mainland. Cuspate forelands, dunes, mudflats and salt marshes, mangroves (the Sundarbans is the largest mangrove forest).

Types of coasts

Emergent coasts: raised beaches and marine terraces (land uplift or fall in sea level).
Submergent coasts: a rise in sea level drowns the land: ria (drowned river valley; the western coast of India has ria-like features), fjord, and the Dalmatian coast.

Coral reefs: built by coral polyps in warm (about 20-25°C), shallow, clear and saline waters.

Fringing reef (attached to the coast), barrier reef (the Great Barrier Reef, Australia), atoll (a ring-shaped reef around a lagoon: Lakshadweep, Maldives). Darwin's subsidence theory explains their succession.

India's coast: about 7,516 km (including islands; the mainland coast is about 6,100 km). The east coast is a coast of emergence (wide plain, deltas); the west coast is submergent (narrow, with estuaries of the Narmada and Tapi).

Key Points

Erosional: cliffs, platforms, caves, arches, stacks, stumps.
Depositional: beaches, spits, bars, lagoons, tombolo.
Chilika: largest brackish-water lagoon in Asia.
Reef types: fringing, barrier, atoll; Lakshadweep and Maldives are atolls.
Emergent coast: terraces; submergent coast: ria, fjord.

MCQs

Q1. A detached pillar of rock left by wave erosion of a headland is a:

(a) Stack
(b) Spit
(c) Tombolo
(d) Bar
Ans:
(a).

Q2. Chilika Lake is a:

(a) Freshwater lake
(b) Brackish-water lagoon
(c) Glacial lake
(d) Oxbow lake
Ans: (b). The largest in Asia.

Q3. Lakshadweep islands are examples of:

(a) Fringing reefs
(b) Barrier reefs
(c) Atolls
(d) Volcanic islands
Ans: (c).