maandag 29 juli 2013

Australia, Lord Howe Island Group

A remarkable example of isolated oceanic islands, born of volcanic activity more than 2,000 m under the sea, these islands boast a spectacular topography and are home to numerous endemic species, especially birds.

Located in the South Pacific, 700 km north-east of Sydney, the property is included administratively in New South Wales. The preserve includes some 75% of the land area of Lord Howe Island and all of the offshore islands and rocks of significant size in the region. These are the Admiralty Group; Mutton Bird and Sail Rock; Blackburn (Rabbit) Island; Gower Island; and Ball's Pyramid, together with a number of small islands and rocks. The seaward boundary follows the mean high water mark and consequently excludes all littoral and marine areas. The entire island group has remarkable volcanic exposures not known elsewhere.
The main island of Lord Howe measures 10 km from north and south and is little more than 2 km in width. It roughly describes a crescent, enclosing a coral reef lagoon on its south-western side. The island's topography is dominated by the southerly Mount Gower and Mount Lidgbird. Only a narrow isthmus of lowland country in the north-central part of the island is habitable. The northern tip consists of steep hillsides culminating in extensive sea cliffs against the northern coastline.
Lord Howe Island is the eroded remnant of a large shield volcano which erupted from the sea floor intermittently for about 500,000 years in the late Miocene (6.5-7 million years ago). The island group represents the exposed peaks of a large volcanic seamount which is about 65 km long and 24 km wide and which rises from ocean depths of over 1,800 m. Four separate series of volcanic rocks are recognized on the main island group: tuffs, breccia and basalts, with widespread intrusion of basaltic dykes. The dominant landforming process on Lord Howe since the last of the volcanic eruptions has been marine erosion, which has cut and maintained major cliffs. Slope failure and accumulation of talus at the foot of some cliffs, especially in the south, have modified their original shape.
The island supports the southern truest coral reef in the world, which is of Pleistocene to Recent Age and differs considerably from more northerly warm water reefs. It is unique in being a transition between the algal and coral reef, due to fluctuations of hot and cold water around the island. A wide variety of vegetation types has been described for the islands, with the diversity corresponding with the range of habitats. Variable exposure to wind and penetration of salt spray appear to be the main determinants of vegetation occurrence, structure and floristic.
 A population of the large forest bat occurs on the Island. No other indigenous native mammals are known. Introduced species, however, include mice, rats and goats.
There are at least 129 native and introduced bird species. Lord Howe is now the only known breeding ground for providence petrel. Fleshy-footed shearwater breeds in large numbers, with possibly half the world's population present seasonally. Other important species breeding within the preserve include kermadec petrel, black-winged petrel, wedge-tailed shearwater, little shearwater, white-bellied storm petrel, masked booby, and red-tailed tropic bird in greater concentrations than probably anywhere else in the world.
The earliest European discovery of Lord Howe appears to have been in 1788 by the British. A small permanent settlement was established in the 19th century, subsisting on trade with passing ships. There is no recognized evidence of prior Polynesian or Melanesian discovery or settlement.

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