A sinking volcanic ridge
The Lakshadweep archipelago is a chain of 36 coral atolls in the Arabian Sea, with a total land area of just 32 square kilometers. These low-lying islands, most averaging only one to two meters above sea level, are built upon the northern segment of the Chagos-Lakshadweep Ridge. This massive underwater feature is a volcanic trace left by the Indian Plate's northward movement over the Réunion hotspot millions of years ago.
Geologically, the ridge is slowly sinking. As the volcanic foundation cools and contracts, it subsides at a rate of 1-2 millimeters per year. Simultaneously, global sea levels are rising due to climate change, with local measurements indicating a rise of around 3 millimeters per year. The combined effect creates a relative sea-level rise of 4-5 millimeters annually, putting the islands in a precarious position. Projections indicate that this could lead to the submergence of significant land area, particularly on islands like Kavaratti and Minicoy, by the end of the century. One uninhabited islet, Parali I, which covered 0.032 square kilometers in 1968, has already been completely lost to erosion.
A biological defense under threat
The islands' primary defense against submergence is the very ecosystem that created them: the coral reef. Healthy coral atolls grow vertically through a process called accretion, where corals and other calcifying organisms build new limestone structures. This biological growth can, in theory, keep pace with or even outpace rising sea levels. The reef acts as a natural breakwater, dissipating up to 75% of wave energy, which protects the islands from erosion and flooding. The sediment produced by the reef—fragments of coral, mollusc shells, and foraminifera—also naturally nourishes and builds the islands themselves.
This natural defense mechanism is failing. Rising sea surface temperatures have caused multiple mass coral bleaching events, with severe occurrences in 1998, 2010, 2016, and 2024. In 2016, sea temperatures reached 31 degrees Celsius, far above the normal threshold for coral survival. Studies show that between 1998 and 2017, the absolute coral cover in Lakshadweep fell from 51.6% to just 11%. While corals can recover from bleaching, they require several years without stress. The increasing frequency of marine heatwaves prevents this recovery, compromising the reef's structural integrity and its ability to grow. Ocean acidification further hinders the corals' ability to build their skeletons. This weakening of the biological engine means the islands are losing their race against the combined forces of geological subsidence and climate change.