The 1970 Bhola cyclone remains one of the deadliest natural disasters in recorded history, killing an estimated 300,000 to 500,000 people across the Ganges-Brahmaputra delta. In its aftermath, as floodwaters receded and sediment patterns shifted, a new sandbar began to break the surface of the Bay of Bengal. Located immediately south of the Hariabhanga River -- the international border river between Bangladesh's Satkhira District and India's South 24 Parganas District in West Bengal -- the island sat at coordinates 21 degrees 37 minutes north, 89 degrees 8 minutes east. It was never more than a low silt deposit in a delta that floods annually, geologically unstable and incapable of supporting permanent habitation. But its position on an international boundary made it immediately significant.

Both India and Bangladesh claimed the island, though neither established permanent settlements on ground that could wash away in any monsoon season. India reportedly hoisted its flag there in 1981 and stationed Border Security Force personnel who patrolled with gunboats. The legal question turned on the thalweg doctrine -- the principle, established by the 1947 Radcliffe Award, that the deepest channel of a border river defines the boundary. If the main channel of the Hariabhanga flowed east of the island, it belonged to India. If west, Bangladesh. India pointed to a 1981 depth survey, corroborated by 1990 British Admiralty and 1991 US National Geospatial-Intelligence Agency charts, showing the deeper channel on the eastern side. Bangladesh countered with its own data, presented during President Ziaur Rahman's visit to India in the late 1970s, placing the main current on the western side. The river, indifferent to cartography, may have shifted its channel between surveys.

In March 2010, Sugata Hazra of the School of Oceanographic Studies at Jadavpur University in Kolkata announced what satellite imagery had already revealed: New Moore Island had disappeared. Rising sea levels, altered monsoon rainfall patterns that changed river flows, and land subsidence had combined to submerge the sandbar entirely. Hazra noted that temperatures in the Bay of Bengal had been rising at roughly 0.4 degrees Celsius per year, and during the 2000s, sea levels in the region rose at a rate of five millimeters annually. The Christian Science Monitor ran the headline, "Global warming as peacemaker?" -- a grim joke about a climate crisis resolving a geopolitical one. The BBC confirmed the story, and the island joined the growing list of landmasses lost to rising oceans.

Even after the island disappeared, the sovereignty question mattered. Maritime boundaries extend outward from territorial baselines, and the island's legal status could influence where those baselines were drawn. In October 2009, Bangladesh had already filed a case with the Permanent Court of Arbitration. The final verdict came in July 2014 -- four years after the island had gone underwater. The court awarded Bangladesh 19,467 square kilometers of the 25,000-square-kilometer disputed maritime area, but placed the location of the former New Moore Island within India's portion. The ruling was final and not subject to appeal. The island's ghost, in a sense, still marks a boundary -- even though the waves now pass uninterrupted over the spot where two nations once planted flags on shifting sand.