Chagos-Laccadive Ridge

Chagos-Laccadive Ridge. It is a major, largely submarine, linear aseismic ridge in the central Indian Ocean, extending southward from the Lakshadweep archipelago off the coast of Kerala, India, to the Chagos Archipelago near the Maldives. This prominent geological feature, spanning approximately 2,500 kilometers, represents the surface expression of the Réunion hotspot track and forms a significant barrier influencing ocean currents and marine ecosystems. The ridge's northern and southern extremities emerge as low-lying atolls and islands, which have played roles in regional maritime history, colonialism, and contemporary geopolitics.

Geography and Geology

The ridge runs in a north-south orientation, broadly parallel to the western coast of the Indian subcontinent. Its northernmost expression comprises the Lakshadweep islands, a union territory of India, while its central section remains submerged as the Maldives Ridge, connecting to the Maldives archipelago. The southern terminus rises as the Chagos Archipelago, including the large atoll of Diego Garcia. Bathymetrically, the ridge separates the deep Arabian Sea to the west from the Central Indian Ocean Basin to the east, creating a shallower platform that affects the flow of major currents like the South Equatorial Current. Geologically, it is composed primarily of basaltic lavas and is overlain by thick sequences of carbonate sediments, forming the characteristic coral reef structures of its emergent parts.

Formation and Tectonic Setting

The ridge is interpreted as the product of the Réunion hotspot, a mantle plume that has been active for over 65 million years. As the Indian Plate moved northward over this stationary hotspot, a chain of volcanic edifices was created, with the oldest rocks found in the northern Deccan Traps of India and progressively younger formations extending southward. This makes the feature a classic example of a hotspot track. The formation of the ridge is intimately linked to the tectonic rifting and seafloor spreading associated with the separation of the Seychelles microcontinent from India, following the breakup of the ancient supercontinent Gondwana. Studies of its magnetic anomalies and dredged rock samples have been crucial in reconstructing the tectonic history of the Indian Ocean.

Biogeography and Ecology

The shallow platforms and atolls of the ridge support diverse and productive marine ecosystems, including extensive coral reefs, seagrass beds, and mangrove forests, particularly in the Lakshadweep and Chagos Archipelago. These areas are recognized for high levels of marine biodiversity and endemism. The British Indian Ocean Territory, which encompasses the Chagos, hosts the world's largest marine protected area, the Chagos Marine Protected Area. The ridge acts as a partial barrier to oceanic circulation, influencing the distribution of pelagic species and creating unique habitats for fauna such as the Chagos brain coral and various species of sea turtle. Its isolation has made it a key site for studying biogeography and the impacts of climate change on coral atolls.

Human History and Exploration

The northern islands of Lakshadweep have been known to Indian and Arab sailors for centuries, referenced in texts like the Periplus of the Erythraean Sea. The Chagos Archipelago was likely discovered by Portuguese explorers like Vasco da Gama in the early 16th century. Control over various segments of the ridge shifted among European colonial powers, with France and later the United Kingdom exerting influence, particularly over the Chagos. The islands were historically used for coconut plantation economies reliant on indentured labor. Significant modern exploration has been conducted by scientific vessels like the RV *Vityaz* and through expeditions by organizations such as the National Institute of Oceanography, India and the Chagos Conservation Trust.

Economic and Strategic Significance

The ridge's economic importance has historically centered on fisheries and copra production. In the modern era, its exclusive economic zones are valuable for tuna fishing. However, its primary significance is geopolitical and strategic. The island of Diego Garcia hosts a major joint military facility operated by the United Kingdom and the United States, serving as a critical base for operations in the Middle East and South Asia. This presence has been a source of ongoing diplomatic controversy, including disputes at the International Court of Justice and the United Nations General Assembly regarding the sovereignty of the Chagos Archipelago and the resettlement rights of the displaced Chagossians. The ridge's location astride key Indian Ocean shipping lanes further amplifies its strategic value.

Category:Indian Ocean Category:Oceanic ridges Category:Geography of Asia Category:Hotspot tracks