Atoll

noun (countable)

/ˈætɒl/

A ring-shaped coral reef, island, or chain of islands enclosing or nearly enclosing a shallow lagoon, typically formed as a volcanic island subsides beneath the sea surface while coral growth continues upward. Charles Darwin's 1842 subsidence theory remains the foundational explanation, later confirmed by drilling at Enewetak Atoll (1952) that revealed over 1,400 m of coral above basalt. In the Indian Ocean, Lakshadweep's 36 islands are classic atolls, making the territory a UPSC-recurring example of coral island formation.

✍️ Usage in a UPSC answer

The Lakshadweep archipelago, comprising 36 atolls rising barely 1–2 m above mean sea level, faces existential threat from accelerating sea-level rise projected at 3–4 mm per year under IPCC AR6 scenarios.

Synonyms

coral ringcoral atolllagoonal reefannular reefreef island

Antonyms

continental islandvolcanic high islandbarrier islandpeninsula

🌱 Word Family

atoll (noun), atollic (adjective, rare)

🔡 Root

Maldivian/Dhivehi atolu = administrative district of coral islands; no Latin root

📜 Etymology

Borrowed into English via Portuguese atol from Maldivian Dhivehi atolu, meaning both a ring-shaped reef and a local administrative unit. First recorded in English in the early 17th century by sailors navigating the Indian Ocean; the geographical-scientific sense was standardised by Darwin's coral-reef studies in 1842.

🧠 Memory Hook

An atoll forms a natural 'O' shape — like the letter in the middle of 'atoll' — enclosing a calm lagoon. Imagine a doughnut (a-TOLL = a ring you pay toll at the gate of a lagoon).

📝 Seen in UPSC Question Papers

Prelims 2018 — Ecology

Real UPSC previous-year questions whose text uses “Atoll” — proof this word earns its place on your list.

🌍 Geography 📖 Seen in: Plate Tectonics & Volcanism — Continen...

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