Indian Geography22 Concepts & Facts

Duncan Passage & Andaman Islands Geography GK

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Duncan Passage is a prominent oceanic strait situated in the Indian Ocean within the Andaman and Nicobar Islands Union Territory of India. Serving as a primary navigable maritime corridor, the passage physically separates Rutland Island (which forms the southern terminal landmass of the Great Andaman archipelago and South Andaman administrative district) to the north from Little Andaman Island to the south. Spanning an east-west orientation, Duncan Passage directly connects the open waters of the Bay of Bengal to the west with the enclosed basin of the Andaman Sea to the east, functioning as an essential sea route for regional shipping, naval patrols, and inter-island passenger transit.

Hydrographically and geographically, Duncan Passage extends across a width of approximately 48 kilometers (roughly 30 miles or 26 nautical miles). Depths across the passage generally vary from 20 to 45 meters, providing sufficient draught for medium and large marine vessels. The passage is not a completely open channel; rather, it is punctuated by several small, ecologically pristine barrier islets, shoals, and coral atolls that require careful navigational plotting. Foremost among these are the Cinque Islands (comprising North Cinque and South Cinque, connected by a spectacular sand isthmus), Passage Island, The Sisters, North Brother Island, and South Brother Island. The marine waters immediately flanking the northern boundary of the passage encompass parts of the Mahatma Gandhi Marine National Park (Wandoor), known for its fragile coral reefs, sea anemones, and nesting sea turtles.

From an overarching strategic and examination perspective, Duncan Passage forms an integral link in the complex system of maritime chokepoints and waterways that define the Andaman and Nicobar archipelago. It operates in close geographical coordination with the Ten Degree Channel (located further south between Little Andaman and Car Nicobar at 10° North latitude), the Sombrero Channel, and the Great Channel (Six Degree Channel) separating Indira Point from Aceh, Indonesia. In modern defense architecture, Duncan Passage falls under the operational jurisdiction of the Andaman and Nicobar Command (ANC)—India’s premier unified tri-service theatre command established in 2001 at Port Blair—which conducts continuous anti-submarine warfare surveillance, maritime interdiction, and exclusive economic zone patrols across this gateway to the Malacca Strait.

Key Concepts & Self-Assessment22 Key Facts

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Duncan Passage is a navigable oceanic strait in the Bay of Bengal and Andaman Sea within the Andaman and Nicobar Islands Union Territory.

The passage physically separates Rutland Island (South Andaman) to the north from Little Andaman Island to the south.

The strait measures approximately 48 kilometers (30 miles / 26 nautical miles) in width across its primary channel.

The water depth in Duncan Passage ranges between 20 and 45 meters, allowing passage for naval vessels and commercial inter-island ships.

It connects the Bay of Bengal on the west with the Andaman Sea on the east.

The Cinque Islands (North Cinque and South Cinque), connected by a submerged sand bar, lie in the northern part of Duncan Passage.

Other prominent islets within the passage include Passage Island, The Sisters (two small islands), and The Brothers (North and South Brother).

Duncan Passage is bordered to the north by the marine ecosystem of the Mahatma Gandhi Marine National Park at Wandoor.

The passage operates as an essential sea lane for ferries and supply ships operating between Port Blair (capital of the territory) and Hut Bay in Little Andaman.

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South of Little Andaman lies the Ten Degree Channel (10° N latitude), which separates the Andaman Islands from the Nicobar Islands (specifically Car Nicobar).

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The Ten Degree Channel is approximately 150 kilometers wide and over 700 meters deep, serving as a primary international shipping lane.

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Further south, the Great Channel (Six Degree Channel) separates Great Nicobar Island (Indira Point) from Sumatra Island of Indonesia.

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The Nine Degree Channel is located in the Arabian Sea, separating Minicoy Island from the main Lakshadweep archipelago.

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The Eight Degree Channel separates Minicoy Island (India) from the Republic of Maldives.

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Little Andaman Island, south of Duncan Passage, is the fourth-largest island in the Andaman archipelago and home to the indigenous Onge tribe.

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Hut Bay on Little Andaman is the administrative headquarters of Little Andaman tehsil and features the island's primary deep-water jetty.

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Duncan Passage is subject to strong tidal currents and tropical squalls, particularly during the onset of the southwest monsoon in May and June.

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The maritime area is under continuous airborne and naval surveillance by the Andaman and Nicobar Command (ANC), headquartered at Port Blair.

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Established in October 2001, the ANC is the only operational unified tri-service command of the Indian Armed Forces, integrating the Army, Navy, Air Force, and Coast Guard.

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The passage forms an integral maritime buffer guarding the western approaches to the Malacca Strait, one of the world's busiest global energy shipping choke points.

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Sea turtles, including the Leatherback turtle (Dermochelys coriacea) and Hawksbill turtle, use the sandy beaches bordering Duncan Passage as critical nesting grounds.

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The Great Nicobar Biosphere Reserve and surrounding waters are recognized for exceptional marine biodiversity, including coral reef systems and dugong feeding zones.

Subject Specialist Commentary

Analytical perspective & practical exam advice from the Master10 academic board

Educator's Insight

Duncan Passage is a navigable strait in the Bay of Bengal that separates Rutland Island in South Andaman from Little Andaman Island. Measuring roughly forty-eight kilometers wide with depths up to forty-five meters, it connects the Bay of Bengal to the Andaman Sea. Dotted with coral islets like the Cinque Islands, this channel provides an essential sea route between Port Blair and Hut Bay, monitored by India's tri-service Andaman and Nicobar Command guarding sea lanes toward the Malacca Strait.

Maritime passages are favorite map-based questions in UPSC prelims and SSC exams. Aspirants often confuse regional channels, so use this mental guide to avoid test traps: Duncan Passage separates South Andaman from Little Andaman, whereas the Ten Degree Channel separates Little Andaman from Car Nicobar. In the Arabian Sea, remember that the Nine Degree Channel separates Minicoy from Lakshadweep, while the Eight Degree Channel separates Minicoy from Maldives. Note also that Little Andaman is home to the Onge tribe.

Duncan Passage & Andaman Islands Geography GK

Key Concepts & Self-Assessment22 Key Facts

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