Coastal Landforms — Geomorphology

Coastal landforms are created by marine erosion, transportation, and deposition. Waves are the principal agent described in these notes.

Coastal Erosional Landforms

Cape, Peninsula, Bay, and Gulf

Where hard and soft rocks occur along a coast, the softer rock is eroded faster. Resistant hard rock may project into the sea, while the sea advances into weaker areas.

Cape: a prominent headland projecting into the sea. Examples include the Cape of Good Hope and Cape Comorin (Kanyakumari).
Peninsula: a comparatively large landmass surrounded by water on three sides and connected to the mainland on the fourth. Examples include the Indian and Arabian peninsulas.
Bay: a broad inlet where the sea extends into the land, generally with a wide opening. The Bay of Bengal is an example.
Gulf: a large inlet that is commonly more enclosed, and often deeper, than a bay, with a narrower opening. Examples include the Persian Gulf, Gulf of Mexico, and Gulf of Mannar.

Creek: a narrow, sheltered inlet of seawater into the land. Sir Creek, between Gujarat in India and Sindh in Pakistan, is an example.
Strait: a narrow channel of water connecting two larger water bodies and separating two landmasses. The Palk Strait separates India and Sri Lanka.
Isthmus: a narrow strip of land connecting two larger landmasses and separating two water bodies. The Isthmus of Panama connects North and South America.

Sea Notch, Sea Cliff, and Wave-Cut Platform

Repeated wave action undercuts the foot of a coastal cliff or headland, forming a sea notch.
Enlargement of the notch destabilizes the rock above, causing collapse. The retreating, steep or nearly vertical rock face is a sea cliff or escarpment.
As the cliff retreats inland, it leaves a gently sloping rocky surface near sea level called a wave-cut platform.

Sea Cave, Arch, Stack, Stump, and Blowhole

These features commonly form in sequence as waves exploit cracks or weak zones in a headland:

Sea cave: a hollow eroded into the base of a cliff.
Sea arch: an opening through a headland, formed when a cave enlarges or caves eroding from opposite sides meet.
Stack: an isolated pillar of rock left offshore after the roof of an arch collapses.
Stump: a low remnant left when a stack is eroded further, often visible only at low tide.
Blowhole or gloup: a near-vertical opening from a sea cave to the land surface. Waves force compressed air and spray through it.

Coastal Depositional Landforms

Bars, Spits, Hooks, and Lagoons

Bar: a ridge of sand or shingle deposited in shallow water, often approximately parallel to the coast.
Barrier bar: a long offshore bar running parallel to the coast and partially shielding the mainland from waves.
Spit: an elongated depositional ridge attached to the mainland at one end and extending into the sea at the other.
Hook: a curved end of a spit, produced when waves or currents alter the direction of sediment transport.
Baymouth bar: a bar that extends across a bay and is attached to land at both ends. The source notes call this a “loop”; baymouth bar is the standard term.
Lagoon or sea lake: a shallow body of seawater separated from the open sea by a bar or barrier. Chilika Lake in Odisha is cited in the notes.

Beach or Wave-Built Platform

A beach is a relatively level or gently sloping accumulation of sediment deposited by waves along the shore. The notes also call a broad depositional surface a wave-built platform. Sediment is graded by wave action: coarser particles generally accumulate higher up the beach, while finer particles tend to remain nearer the water.

Tombolo

A tombolo is a bar of deposited sediment that connects an island to the mainland, or sometimes connects two islands.

Marine Dunes

Sediment deposited on the coast can be picked up by onshore winds and carried inland, where it accumulates in different dune forms. These marine or coastal dunes are classified as aeolian depositional landforms because wind is the immediate agent of their formation.