Coastline, Coastal Plains, and Indian Islands

India's Coastline — 2025 Revised Length

Critical Update (April 2025): India's coastline was officially revised from 7,516.6 km to 11,098.81 km by the National Hydrographic Office (NHO) in coordination with the Survey of India. The revision was promulgated by the Ministry of Ports, Shipping and Waterways (MoPSW) circular dated April 29, 2025, after acceptance by the Coastal Protection and Development Advisory Committee (CPDAC) and concurrence from all coastal states/UTs.

Why the increase? (Not territorial expansion)

• Old measurement: smaller-scale maps at 1:1,000,000 — missed fine coastal details.
• New measurement: high-resolution GIS data at 1:250,000 scale — captures every creek, estuary, backwater, and coastal indentation.
• India's territory has not expanded — only the measurement methodology improved.
• This is the first revision in ~50 years — based on satellite imagery + modern geospatial tools.

Updated State/UT-wise Coastline (Post-2025 Revision)

Ranking change: Tamil Nadu (2nd) has overtaken Andhra Pradesh (3rd) in the revised measurement. West Bengal's dramatic increase (+563 km) is due to finer measurement of the Sundarbans mangrove coastline.

Coastal States and UTs

• India's coast is touched by 9 States and 4 Union Territories.
• States: Gujarat, Maharashtra, Goa, Karnataka, Kerala, Tamil Nadu, Andhra Pradesh, Odisha, West Bengal.
• UTs: Lakshadweep, Andaman & Nicobar Islands, Puducherry, Dadra & NH and Daman & Diu.

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Characteristics of India's Coastline

Straight Coastline — Origins

• India's coastline is largely straight and regular — formed by faulting of the Gondwana landmass during the Cretaceous period (~66 Ma).
• When the peninsula was rifted away from Africa, the western margin became a fault scarp (now the Western Ghats cliff face), and the coast was left straight.
• Contrast: European coastlines are highly indented (rias, fjords, bays) — formed by submergence of river valleys and glacial erosion; this provides many excellent natural harbours.

Natural Harbours — Limited

• India's straight coastline provides very few natural harbours despite its long coast.
• Indented coastlines → sheltered inlets, creeks, estuaries → easy port construction and maintenance.
• India compensates with artificial/engineered ports (Visakhapatnam, Chennai, Nhava Sheva/JNPT).
• Natural harbour exceptions: Visakhapatnam (east, protected by headlands), Mumbai (Ulhas estuary + Thane Creek), Kochi (backwater inlet).

Coastlines of Emergence and Submergence

Western coast = submerged → narrow plain, many inlets → excellent harbours. Eastern coast = emergent → wide shallow shelf → poor harbours, difficult port construction.

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Western Coastal Plains

Western coastal plains stretch from the Rann of Kachchh (north) to Kanyakumari (south) — approximately 1,500 km long.

Key characteristics:

• Average width: 65 km — narrower in the middle (Karnataka/Goa), wider toward north (Gujarat) and south (Kerala).
• Rivers flowing through this plain do not form deltas (too steep a gradient to the sea).
• Example of a submerged coastline — submergence creates natural harbours.
• Major ports: Kandla, Mazagaon, JNPT (Nhava Sheva), Marmagao, New Mangalore, Kochi.

Sub-regions (North to South)

1. Kutch and Kathiawar Region (Gujarat)

• Kutch Peninsula: Extension of the Peninsular plateau in Gujarat; now an arid/semi-arid environment.
  • Great Rann of Kutch: Salt-soaked flat plain north of Kutch — seasonal wetland; India's largest salt desert; borders Pakistan.
  • Little Rann of Kutch: Southern extension — SE of Kachchh; habitat of the Indian Wild Ass (Equus hemionus khur) — Sanctuary established here.
  • Historical context: Kutch was once an island surrounded by seas and lagoons; Indus River sediments filled the water bodies over millennia.
• Kathiawar Peninsula: South of Kachchh.
  • Mandav Hills (radial drainage pattern)
  • Mt Girnar (1,117 m) — highest peak of Gujarat; volcanic origin.
  • Gir Range — southern Kathiawar; Gir National Park — only wild habitat of the Asiatic Lion.

2. Gujarat Plain

• Situated east of Kachchh and Kathiawar.
• Shaped by rivers: Narmada, Tapti, Mahi, Sabarmati → drains into Gulf of Khambhat (Cambay).
• Eastern part: fertile; coastal areas: windblown loess → semi-arid landscape.

3. Konkan Plain (Maharashtra and Goa)

• Stretches from Daman to Goa — between Gujarat Plain and Karnataka coast.
• Exhibits marine erosional features (sea cliffs, sea caves, rocky inlets).
• Thane Creek (Mumbai): significant embayment forming an excellent natural harbour → basis for Mumbai's port.
• Width: very narrow (~50 km); terrain broken and hilly close to the Western Ghats.

4. Karnataka Coastal Plain

• From Goa to Mangalore — also called the Kanara coast.
• Marine topography very marked; numerous sea stacks, sea arches.
• Western Ghats streams cascade down steep slopes forming waterfalls:
  • Sharavati River → Jog (Gersoppa) Falls — one of India's highest waterfalls (~253 m).

5. Kerala (Malabar) Plain

• From Mangalore to Kanyakumari — widest segment of the western coastal plain.
• Characterised by: lakes, lagoons, backwaters, spits.
• Kayals/Backwaters: Shallow lagoons or inlets running parallel to the coastline — separated from the sea by narrow sand bars (spits).

• Kuttanad region: Below sea level paddy cultivation using an intricate system of bunds — only region in India with below-sea-level farming (Ramsar Site).
• The backwaters (Kayals) are used for transport, fishing, coconut processing, and tourism (houseboat industry).

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Eastern Coastal Plains

Eastern coastal plains stretch from the Subarnarekha River (West Bengal–Odisha border) to Kanyakumari — approximately 1,500 km long.

Key characteristics:

• Average width: 120 km — significantly wider than western coast.
• Emergent coast with an extensive continental shelf (extends up to 500 km into the sea).
• Sea is too shallow for deep-draught ships → very few natural harbours.
• Major rivers form large deltas: Mahanadi, Godavari, Krishna, Cauvery.

Sub-regions (North to South)

6. Utkal Plain (Odisha)

• Coastal areas of Odisha including the Mahanadi Delta.
• Most notable feature: Chilika Lake — India's largest brackish water (saline) lake and Asia's largest lagoon.
  • A Ramsar Site (Wetland of International Importance).
  • Famous for migratory birds, Irrawaddy dolphins, and olive ridley turtles.
• South of Chilika: low hills interrupt the coastal plain.

7. Andhra Plain (Northern Circars + Southern Andhra)

• From Utkal Plain south to Pulicat Lake.
• Northern Circars: coastal strip between Mahanadi and Krishna rivers.
• Key feature: Godavari–Krishna delta — two deltas have merged into a single physiographic unit (world's third-largest delta system).
• Kolleru Lake: Freshwater lake between Godavari and Krishna deltas — originally coastal lagoon, now inland due to delta advancement.
• Pulicat Lake (Andhra–Tamil Nadu border): India's second largest brackish water lake; blocked by Sriharikota Island (ISRO launch site — SDSC SHAR).
• Coastline: straight, lacks good natural harbours except Visakhapatnam (natural deep-water harbour protected by headlands) and Machilipatnam.

8. Tamil Nadu Plain (Carnatic and Coromandel)

• From Pulicat Lake to Kanyakumari — average width 100 km; widens to 130 km at the Cauvery Delta.
• Carnatic: Region between Krishna and Cauvery.
• Coromandel Coast: Combined Tamil Nadu coast + southern Andhra coast — characterised by:
  • Receives rainfall from the Northeast (Retreating) Monsoon (Oct–Dec) — opposite to rest of India.
  • Flat, sandy, few natural harbours.
  • Chennai (Madras) — artificial harbour (entirely man-made, no natural protection).
• Cauvery Delta: The "granary of South India" — fertile soil + ample irrigation.
• Also called Payan Ghat in some older texts.

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Significance of Coastal Plains

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Indian Islands

India has two major island groups plus scattered minor islands:

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Andaman and Nicobar Islands

Geological Origin

• Formed due to the collision between the Indian Plate and the Burma Minor Plate (part of the Eurasian Plate) in the Bay of Bengal.
• These islands are a southward extension of the Arakan Yoma range in Myanmar, which itself is an extension of the Purvanchal Hills.
• Part of the Pacific Ring of Fire arc extending from Sumatra (Indonesia) through Myanmar to the Andamans.

Geographic Extent

Key Channels

Andaman Group

• Great Andaman: North, Middle, and South Andaman — closely knit group of ~200 islands.
• Little Andaman: Separated from South Andaman by the Duncan Passage.
• Port Blair (capital) situated in South Andaman.
• Saddle Peak (737 m) in North Andaman — highest peak in the entire A&N archipelago.

Volcanic Islands:

Barren Island — Updated (2025): Active Strombolian eruptions ongoing since 1991. Eruptions in 2017, 2022, March–April 2024, and October 2025 (ash plume to 10,000 ft / 3,000 m). New lava flows reported from the northern flank vent. The 1991 UPSC statement claiming "last eruption was 1991 and it has remained inactive since" is factually incorrect.

[UPSC Prelims 2018] Barren Island volcano statements:

1. Active volcano in Indian territory ✓
2. ~140 km east of Great Nicobar ✗ (it is ~135 km NE of Port Blair, which is in South Andaman — not east of Great Nicobar)
3. Last eruption was 1991, inactive since ✗ (erupted multiple times since: 1994–95, 2005, 2008, 2010, 2017, 2022, 2024, 2025) Answer: a) 1 only ✓

Nicobar Group

• 7 large + several small islands south of the 10° Channel.
• Car Nicobar: Northernmost island of the Nicobar group; Indian Air Force base.
• Great Nicobar: Largest and southernmost island; closest to Sumatra (Indonesia) — ~150 km away.
  • Indira Point (Pygmalion Point) at Great Nicobar = India's southernmost point (6°45'N).
  • Indira Point was partially submerged in the 2004 Indian Ocean Tsunami (December 26, 2004).
• These islands receive convectional rainfall and have equatorial-type vegetation (tropical wet evergreen forests).
• Rock composition: Tertiary sandstone, limestone, and shale; some coral deposits on coasts.

[UPSC Prelims 2014] Which islands are separated by the Ten Degree Channel? a) Andaman and Nicobar ✓ b) Nicobar and Sumatra c) Maldives and Lakshadweep d) Sumatra and Java

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Lakshadweep Islands

Origin and Type

• Coral atolls — not tectonic; formed over a submarine volcanic ridge (the Chagos-Lakshadweep Ridge).
• Associated with Reunion Hotspot volcanism — the underwater seamounts provided a base on which coral grew.
• No recent volcanism or tectonic activity (unlike A&N).

Geographic Facts

Key Islands

Sub-groups of Lakshadweep

• Aminidivi Islands: 6 main islands (northernmost group)
• Laccadive Islands: 5 major islands; Kalpeni and Kavaratti are the prominent ones
• Minicoy Island: Southernmost island; separate from main Laccadive group

Physical Characteristics

• Topography: Flat, no hills or valleys; low-lying (most islands <5 m above sea level).
• Storm beaches: Unconsolidated pebbles, shingles, cobbles, boulders.
• Highly vulnerable to sea level rise — even a 1–2 m rise would inundate most islands.
• No rivers or streams (too flat and small).
• Coral bleaching events (2016, 2020, 2024) threaten the reef ecosystem on which islands depend.

Important Channels Around Lakshadweep

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Other Notable Islands

New Moore Island (South Talpatti)

• Small uninhabited sandbar in the Bay of Bengal; off the Ganges–Brahmaputra delta.
• Emerged after the Bhola Cyclone (1970) — intermittently appears and disappears.
• Disputed between India and Bangladesh — both claimed it due to potential oil and gas reserves; also tied to the Radcliffe Award maritime boundary dispute.
• Largely submerged for extended periods; not permanently above water.

Sagar Island (Ganga Sagar)

• Situated in the Ganga delta (Hooghly mouth), West Bengal; on the continental shelf.
• Famous for Ganga Sagar Mela — one of the largest Hindu pilgrimages after the Kumbh Mela (held every Makar Sankranti, January 14).

Pamban Island (Rameswaram Island)

• Connects to Tamil Nadu mainland via Pamban Bridge (India's first sea bridge; opened 1914).
• Separated from Sri Lanka by the Palk Strait (~22 km at Adam's Bridge/Rama Setu).
• Rameswaram (one of the Char Dhams) is located here.

Islands Near Sri Lanka

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UPSC Corner

Key One-Liners for Prelims

• India's total coastline (official, April 2025): 11,098.81 km (revised from 7,516.6 km)
• Coastline revision: old measurement used 1:1,000,000 maps; new uses 1:250,000 GIS data
• Longest coastline state: Gujarat (~2,340 km) — highest gain (+1,125 km) in the revision
• Ranking (updated): 1. Gujarat 2. Tamil Nadu 3. Andhra Pradesh 4. West Bengal 5. Maharashtra
• India's coast: 9 states + 4 UTs; total continental shelf extends up to 500 km in the east
• Western coast = submerged (narrow, good harbours); Eastern coast = emergent (wide, poor harbours)
• Vembanad Lake: India's longest lake (~97 km); largest backwater in Kerala
• Chilika Lake: India's largest brackish water lake; Asia's largest lagoon; Odisha; Ramsar Site
• Pulicat Lake: 2nd largest brackish water lake; bordered by Sriharikota (ISRO SDSC SHAR)
• 10° Channel: separates Andaman (north) from Nicobar (south)
• Duncan Passage: separates Little Andaman from South Andaman
• Barren Island: Only active volcano in India; ~135 km NE of Port Blair; Strombolian eruptions ongoing (last reported: October 2025)
• Narcondam: Dormant/extinct volcano; A&N Islands
• Saddle Peak (737 m): Highest peak in A&N archipelago; North Andaman
• Indira Point (6°45'N): India's southernmost point; Great Nicobar; partially submerged in 2004 Tsunami
• Lakshadweep: Coral atolls; 36 islands; smallest UT in India; renamed 1973 (was Laccadive, Minicoy, Amindivi)
• Andrott: Largest island in Lakshadweep; Kavaratti: Capital; Agatti: only airport
• Minicoy: Southernmost island of Lakshadweep; Aminidivi: Northernmost
• 8° Channel: Minicoy (north) from Maldives (south); 9° Channel: main Lakshadweep from Minicoy
• Lakshadweep elevation: mostly <5 m above sea level — extremely vulnerable to sea level rise
• Jog (Gersoppa) Falls: Sharavati River; Karnataka coast; ~253 m — forms as western Ghats stream descends to coast

Mains GS1 Questions

1. "Compare and contrast the Western and Eastern Coastal Plains of India in terms of origin, width, drainage, and economic significance."
2. "The backwaters (Kayals) of Kerala are a unique geographical feature. Discuss their formation, significance, and the challenges they face."
3. "Examine the significance of the Andaman and Nicobar Islands for India's strategic and economic interests."
4. "Why was India's coastline recently revised from 7,516 km to 11,098 km? Does this imply any territorial change? Discuss the implications of this revision."

MCQ Trap Awareness

• Trap: "India's coastline is 7,516.6 km" → Outdated — officially revised to 11,098.81 km (MoPSW, April 29, 2025).
• Trap: "India's coastline increased due to territorial expansion" → Wrong — increase is due to better GIS measurement at finer scale (1:250,000), not territory.
• Trap: "Gujarat has the longest coastline of 1,214 km" → Old figure — updated to ~2,340 km (post-2025 revision).
• Trap: "Andhra Pradesh has the second-longest coastline" → Outdated — Tamil Nadu is now 2nd (~1,069 km), AP is 3rd (~1,053 km) after revision.
• Trap: "Chilika Lake is in Tamil Nadu" → Wrong — Chilika is in Odisha (between Puri and Ganjam districts).
• Trap: "Pulicat Lake is India's largest brackish water lake" → Wrong — Chilika is the largest; Pulicat is second.
• Trap: "Barren Island last erupted in 1991" → Wrong — has erupted multiple times since 1991; last reported activity: October 2025 (ongoing).
• Trap: "Barren Island is east of Great Nicobar" → Wrong — it is ~135 km NE of Port Blair (South Andaman); Great Nicobar is the southernmost island.
• Trap: "Lakshadweep consists of 12 islands" → Wrong — 36 islands total; 10 inhabited islands.
• Trap: "Andrott is the capital of Lakshadweep" → Wrong — Kavaratti is the capital; Andrott is the largest island by area.
• Trap: "The 9° Channel separates Lakshadweep from Maldives" → Wrong — 8° Channel separates Minicoy from Maldives; the 9° Channel separates main Lakshadweep from Minicoy.
• Trap: "Saddle Peak is in South Andaman" → Wrong — Saddle Peak (737 m, highest in A&N) is in North Andaman.
• Trap: "Western coast rivers form large deltas" → Wrong — Western coast rivers do not form deltas (rivers too short and steep); delta formation is characteristic of the eastern coast.
• Trap: "Kuttanad farming is below sea level only during monsoon" → Wrong — Kuttanad is permanently below sea level; it is India's only below-sea-level farming region (not seasonal).