One Tree Reef is one of fourteen reefs in the Capricorn Group, southern Great Barrier Reef. The reef has an asymmetrical triangular shape, 5.5 km long and 3 km wide, with a small coral shingle cay on the southeastern corner. One Tree Reef evolved from a karst carbonate platform, now 10 to 25m below sea level, but emergent during the last sea-level low before 9600-9000 years B.P. With rising sea level, vertical organic accretion was dominant, although there was some lateral accretion on the higher southeastern corner. By 4400 years B.P. the reef grew up into the influence of the present wind-induced southeasterly wave regime. Present reef shape approximates a bow of a ship facing into wind, with the resultant wave refraction and diffraction producing a symmetrical energy pattern which has influenced the present sediment pattern. This pattern is symmetrical about a lagoonal axis of interaction of wave fronts. Present lagoonal sedimentation is controlled by flood tide and swash or wave surge transport, swash sorting and slack water periods when sediment in suspension is deposited.
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