. Atoll research bulletin. Coral reefs and islands; Marine biology; Marine sciences. 14 50-100 LEACHING & SOLUTION. ASTHENOSPHERIC BUMP Figure 6. Idealized history of an atoll emerging-subsiding as it passes over an asthenospheric bump. After Menard (1973). due to the islands own mass. Although some atolls have been subsiding for more than 50 ml years and have undergone subsidence exceeding 1,000 m it is very unlikely that isostasy alone could occur over such long periods of time. McNutt and Menard (1978) suggest that lithospheric loading by a new volcanic island produces a response over g
. Atoll research bulletin. Coral reefs and islands; Marine biology; Marine sciences. 14 50-100 LEACHING & SOLUTION. ASTHENOSPHERIC BUMP Figure 6. Idealized history of an atoll emerging-subsiding as it passes over an asthenospheric bump. After Menard (1973). due to the islands own mass. Although some atolls have been subsiding for more than 50 ml years and have undergone subsidence exceeding 1,000 m it is very unlikely that isostasy alone could occur over such long periods of time. McNutt and Menard (1978) suggest that lithospheric loading by a new volcanic island produces a response over geologic time scales of 100,000 years or more, while Watts and Cochrane (1974) state that after only a few million years of loading isostatic adjustments approach zero and that the ocean plate then seems capable of supporting seamount chains for periods of tens of millions of years. Isostatic subsidence, for newly formed volcanic islands and submerged seamounts is very real, however, and immediately gives rise to a "moat-arch" development (McNutt and Menard, 1978, 1979; Jarrard and Turner, 1979). Depression of the lithosphere by a new volcanic mass is variously described as crustal loading or lithospheric loading, and a crustal moat develops peripheral to the seamount. This moat may fill rapidly with sediments and not appear on bathymetric maps. Beyond the outer edge of the moat, flexuring develops an arch which experiences uplift in the order of tens of metres. If there are islands at various distances from this new loading mass those within the developing moat will experience gradual subsidence, while those on the developing arch will be slowly elevated. McNutt and Menard (1978) argue that the uplift of Atui, Mitiara, Mauke and Mangaia atolls in the Cook Islands result from lithospheric loading by three nearby volcanoes. Jarrard and Turner (1979), while agreeing with this conclusion, disagree as to the exact amount of resultant elevational change. When magmatic outpo
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