![]() It has two densely vegetated cays, which lie close together on the windward lagoonal terrace near the border of the lagoon basin. 1996a).Īlbuquerque Cays atoll, about 35 km SW of San Andrés, is the only atoll in the area that has a roughly circular outline, with a diameter of about 8 km ( Figs. Two (formerly three) small sandy cays and a tiny sand spit are the only emergent portions of the atoll ( Díaz et al. The lagoon is quite open to the leeward side. It is kidney-shaped and nearly 13 km long in a NW-SE direction. Jaime Garzón-Ferreira, Juan Manuel Díaz, in Latin American Coral Reefs, 2003 2.2 Courtown, Albuquerque and Roncador atollsĬourtown atoll lies 22 km ESE from San Andrés. It is often observed that the dominant constituents of reef-island sediments vary from atoll to atoll, across the globe ranging from coral or crustose coralline algae to calcareous green algae called Halimeda (Caribbean Islands) and foraminifera (dominate on Pacific atolls) ( Yamano et al., 2005). For these reasons, they have developed some degree of dynamic equilibrium with current climate and oceanographic environment, but are continually subject to readjustment, erosion and sedimentation, in response to varying sea levels, wind patterns and storms. But depending on rates of sea level rise (SLR) and coral productivity, reefs may keep up with sea level, fall behind (becoming submerged), or catch up if the rate of SLR diminishes or productivity increases ( Neumann and Macintyre, 1985). However, during the geological period the sea level has changed. ![]() A typical example of this kind is Kaafu Atoll, Maldives and Agatti Island, Lakshadweep, India ( Fig. 1.5). In general, atolls lack an emergent volcanic core and are characterised by very low maximum elevations, limited land area, and thin freshwater lenses ( Singh et al., 2009). The atolls and atoll reef islands observed today are geologically young features, having formed on older foundations since global sea level stabilized about 6000 years ago ( Bard et al., 1996). Darwin (1842) referred to barrier reefs surrounding volcanic islands as an intermediate stage in the development of atolls through long-term subsidence and reef growth. Atolls are more or less annular reef and reef-island systems found mostly in oceanic mid-plate settings, where they rest on the peaks of submarine volcanic edifices.
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