Thursday, June 03, 2010

South Pacific Coral Islands Growing

A study of twenty-seven islands in the Pacific Ocean has shown that twenty-three of the islands have grown in size or stayed the same in the last sixty years. This is despite sea levels rising nearly five (4.7) inches (120 millimeters).

The key part of the study is below:

[Arthur] Webb [of the South Pacific Applied Geoscience Commission in Fiji] says the trend is explained by the islands' composition. Unlike the sandbars of the eastern US coast, low-lying Pacific islands are made of coral debris. This is eroded from the reefs that typically circle the islands and pushed up onto the islands by winds, waves and currents. Because the corals are alive, they provide a continuous supply of material. "Atolls are composed of once-living material," says Webb, "so you have a continual growth." Causeways and other structures linking islands can boost growth by trapping sediment that would otherwise get lost to the ocean.

All this means the islands respond to changing weather and climate. For instance, when hurricane Bebe hit Tuvalu in 1972 it deposited 140 hectares of sedimentary debris onto the eastern reef, increasing the area of the main island by 10 per cent.

The study was done by looking at areal imagery of the islands from the past sixty years. The study shows that at least some Pacific islands have an active growth cycle which can protect them from sea level rise. However, not all the islands have this mechanism. So threat of submersion for other, non-coral Pacific islands still exists.

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