Houtman Abrolhos

Travel Guide Oceania Australia Western Australia Houtman Abrolhos



The Houtman Abrolhos (often informally called the Abrolhos Islands) is a chain of 122 islands, and associated coral reefs, in the Indian Ocean off the west coast of Australia. Nominally located at 28°43′S 113°47′E, it lies about eighty kilometres west of Geraldton, Western Australia. It is the southernmost true coral reef in the Indian Ocean, and one of the highest latitude reef systems in the world. It is one of the world's most important seabird breeding sites, and is the centre of Western Australia's largest single-species fishery, the western rock lobster fishery. It has a small seasonal population of fishermen, and a limited number of tourists are permitted for day trips, but most of the land area is off limits as conservation habitat. It is well known as the site of numerous shipwrecks, the most famous being the Dutch ships Batavia, which was wrecked in 1629, and Zeewijk, wrecked in 1727.




The Houtman Abrolhos is made up of three island groups, the Wallabi Group, Easter Group and Pelsaert Group.

The most northerly group, the Wallabi Group, consists of an island clump about 17 kilometres by 10 kilometres, and also takes in the outlying North Island, located 14 kilometres to the northwest. The main islands of the Wallabi Group are North Island, West Wallabi Island, East Wallabi Island and Beacon Island. The group is best known for the shipwreck of the Batavia on Morning Reef near Beacon Island in 1629,[4] and the subsequent mutiny and massacre that took place among the marooned survivors.

The Easter Group lies to the southeast of the Wallabi Group, from which it is separated by a 9 kilometres wide channel named Middle Channel. It is about 20 kilometres by 12 kilometres, and consists of a number of islands including Rat Island, Wooded Island, Morley Island, Suomi Island and Alexander Island.

Further to the southeast, across Zeewijk Channel, lies the Pelsaert Group, the most southerly true coral reef in the Indian Ocean. The main islands of this group are Middle Island, Square Island, Long Island, Pelsaert Island, Basile Island and the Mangrove Group. A great many ships have been wrecked in the Pelsaert Group, most notably the Zeewijk, which was wrecked on the Half Moon Reef in 1727, the survivors staying on Gun Island for some time afterwards. Other wrecks include the Ocean Queen, wrecked on the Half Moon Reef in 1842; the Ben Ledi, wrecked off Pelsaert Island in 1879; and the Windsor, wrecked on the Half Moon Reef in 1908.




The islands have a Mediterranean climate, with warm dry summers and cooler, wet winters. Mean temperatures range from 9.3 °C to 19.5 °C in July, and from 19.1 °C to 32.4 °C in February. These temperatures have a substantially smaller range than on the mainland: the summer temperature is typically a degree cooler, while winter temperatures are a good deal warmer. This is due to the influence of the ocean, and to the Leeuwin Current.

86% of the rain falls between April and September; on average there are 89 raindays, resulting in 469 millimetres of rain. The wettest month is June, when over 100 millimetres typically falls. In contrast, only about 70 millimetres can be expected to fall between October and March.

It is nearly always windy. During summer a high pressure ridge lies to the south, causing persistent winds from the southeast or southwest, at speeds exceeding 17 31 km/h almost half the time. During autumn and winter, the ridge moves northwards, increasing the atmospheric pressure over the islands, resulting in highly variable winds. Winter tends to produce both the strongest gales and the most frequent periods of calm.

In addition to these winds, there is daily pattern of land breezes in the morning, followed by the onset of south-westerly sea breezes in the afternoon. This pattern is caused by temperature differences between the land and the ocean, and is not as strong in the Houtman Abrolhos as on the mainland, but is present nonetheless.

Three classes of storm have been identified for the region. Brief squalls may occur between December and April. A tropical cyclone occurs in the area about once in three years, between January and April; these may generate extremely high wind speeds that are potentially destructive. During winter, extra-tropical cyclones sometimes pass south of Geraldton, generating winter gales with gusts of up to 35 metres per second, the wind direction from the northwest initially, then gradually moving around to southerly.





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This is version 2. Last edited at 8:41 on Jul 24, 17 by Utrecht. 2 articles link to this page.

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