New model of reef-island evolution: Maldives, Indian Ocean

A new model of reef-island evolution, based on detailed morphostratigraphic analysis and radiometric dating of three islands in South Maalhosmadulu Atoll, Maldives, is presented. Islands initially formed on a foundation of lagoonal sediments between 5500 and 4500 yr B.P. when the reef surface was as much as 2.5 m below modern sea level. Islands accumulated rapidly during the following 1500 yr, effectively reaching their current dimensions by 4000 yr B.P. Since then the high circum-island peripheral ridge has been subject to seasonal and longer-term shoreline changes, while the outer reef has grown upward, reducing the energy window and confining the islands. This new model has far-reaching implications for island stability during a period of global warming and raised sea level, which will partially reactivate the energy window, although it is not expected to inhibit upward reef growth or compromise island stability.