Flight 41B; 23S, 135W, 9 Feb 1984
Iles Gambier is seemingly an anomaly in the Tuamotu Archipelago, in which 95% of the islands are atolls. This extraordinary island-barrier reef complex is in the southeasternmost end of the Tuamotus, some 120 kilometers from the mature Groupe Acteon. Clearly on a subsiding platform, the reef and lagoon indicate such rapid sinking that shallow lagoonal beaches and lagoonal coral knolls are precluded, except in the very northwest corner. This barrier reef system is in sharp contrast to that of Bora-Bora, where broad coral beaches and a gleaming white shoal lagoon have expanded on a gradually subsiding island mass. The platform on which Iles Gambier sits is undergoing complex subsidence apparent from the topography of the island-reef complex. The reef exposed on the northeast has subsided to depths greater than 75 meters compared to the southwest of the main island. This differential rate is probably created by a submarine fault.
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