Fairfax Islands - Geomorphology and Landscape

Geomorphology and Landscape

The eastern cay is composed of shingle and the western of sand and shingle. Interference with the vegetation of the eastern cay occurred as a result of phosphate mining and secondly during the period when the Australian Military Forces used the area as a bombing target. The cay is no longer used for either purposes. Vegetation is dominated by Pisonia grandis which is restricted to the centre of the island. Two brackish pools are located towards the eastern end of the island.

The western cay features an elongated sand spit that supports vegetation on its western extremity. Vegetation is similar to that occurring on the larger sand cays of the Capricorn Group. A tin shed, erected by the Australian Navy when the eastern cay was used for bombing practice, is located in the centre of the island.

The Capricorn and Bunker Cays form part of a distinct geomorphic province at the southern end of the Great Barrier Reef (Hopley 1982). The cays and their reefs lie on the western marginal shelf, and are separated from the mainland by the Curtis Channel. The cays are not generally visible from the mainland, although Masthead Island may be viewed from Mount Larcom on a clear day.

Geologically the cays are young, having developed during the Holocene period, they are mostly around 5000 years old. The sea level was much lower during the last Ice Age (at the end of the Pleistocene period) and the coastal plane on which today’s reefs and cays developed was completely exposed. Early in the Holocene (around 10,000 years ago) the sea level began to rise, until it stabilised at its present level around 6000 years ago. Once the sea level stabilised, it was possible for reef flats to expand and provide potential sites for the formation of cays.

Fairfax Islands area a Closed Ring Reefs and the two coral cays belong to two distinct types:

• 1. Vegetated sand cays:- Fairfax (West).
• 2. Shingle cays:- Fairfax (East).