UPSC Prelims 2023 Q5: Falling Sea Levels and Coastal Marshlands
Which one of the following is the best example of repeated falls in sea level, giving rise to present-day extensive marshland?
- Bhitarkanika Mangroves
- Marakkanam Salt Pans
- Naupada Swamp
- Rann of Kutch
Answer: (d) Rann of Kutch
Statement-wise explanation
- a: incorrect — Bhitarkanika is a mangrove wetland in the Brahmani–Baitarani delta in Odisha. It became a Ramsar site in 2002 and the Ramsar site covers about 650 sq km. It formed where river silt builds up on a tidal coast, so it is a deltaic and intertidal feature. Repeated withdrawals of the sea did not create it.
- b: incorrect — The Marakkanam salt pans in Villupuram district, Tamil Nadu, cover about 4,000 acres and are one of the state's largest sources of salt. People make these pans by letting seawater into shallow beds and evaporating it. They are not a natural marshland left behind as the sea level fell.
- c: incorrect — Naupada in Srikakulam district, Andhra Pradesh, is a small coastal wetland of swamps, mudflats and creeks. It is known as the 'Salt Bowl of Andhra Pradesh' for its salt fields. It is a local tidal swamp, not an extensive marshland made by repeated falls in sea level.
- d: correct — The Rann of Kutch was a shallow arm of the Arabian Sea. The sea flooded it after the last Ice Age, then withdrew during the late Holocene. Cycles of the sea advancing and retreating, together with uplift of the land, left behind flat beds of saline clay. The result is a vast seasonal salt marsh: it floods in the monsoon and dries into a white salt desert in winter.
How to eliminate
The key words are 'repeated falls in sea level' and 'extensive'. Ask which option is a large landform the sea once covered and then left. Salt pans are made by people for salt production, so Marakkanam drops out. Naupada is also a small salt-making swamp, so it is not 'extensive'. Mangroves grow in the tidal zone of deltas, where the sea still reaches every day, so Bhitarkanika does not fit a sea that has retreated. That leaves the one option that is huge, flat, salty and now mostly cut off from the sea. If you know only one fact, remember this: the Rann of Kutch is a former gulf of the Arabian Sea that the sea abandoned. That is why its surface is salt-crusted clay rather than sand.
Know more
Emergent coasts and relict marine landforms
When the sea level falls compared with the land, the coast is called emergent. This can happen because the sea itself drops (eustatic change, such as during ice ages) or because the land rises (tectonic or isostatic uplift). Former seabed and tidal flats are then exposed. They are flat, low-lying and full of salt, because the seawater left behind evaporates.
In the Rann of Kutch, the sea rose after the last glaciation and filled a shallow gulf. Later it withdrew, helped by tectonic uplift; Kutch is one of India's most earthquake-prone zones. Each time the sea advanced and retreated, it left more clay and salt. The monsoon now floods the Rann for a few months. In winter the water evaporates and a salt crust forms. Harappan Dholavira, on Khadir island inside the Rann, is evidence that the shoreline was once much closer to this area.
| Feature | How it forms | Sea still reaches it? | Example |
|---|---|---|---|
| Relict salt marsh | Sea withdraws from a shallow gulf; salt and clay are left behind | Only in floods or storms | Rann of Kutch |
| Mangrove swamp | Silt builds up in the tidal zone of a delta | Yes, twice a day | Bhitarkanika, Sundarbans |
| Coastal lagoon | A sandbar or spit encloses seawater | Through an inlet | Chilika, Pulicat |
| Salt pan | People evaporate seawater in shallow beds | Seawater is let in by people | Marakkanam, Naupada |
Submergent vs emergent coasts: Rias and fjords are drowned valleys and show a rise in sea level. Raised beaches, coastal plains and relict marshes show a fall. India's east coast is mostly an emergent coast with wide plains. The west coast is narrower and more indented.
NCERT Concepts to Revise
- Rann of Kachchh: Defines the Rann of Kachchh as a seasonal salt marsh, the type of landform the question asks about.
- Sea level rise: The question is about sea-level change. This entry explains the opposite process, a rise, so you can contrast the two.
- Isostasy: Land rising through isostatic or tectonic movement is one way the sea 'falls' relative to a coast.
- Bhitarkanika mangroves: Helps you judge whether a deltaic mangrove forest fits a landform made by a retreating sea.
- Dholavira: Dholavira, on an island inside the Rann, is a clue to where the old shoreline of this region lay.