Macquarie Island, Australia

in Wonders of Islands Wonders of Nature by admin — January 12, 2011 at 7:53 pm | 0 comments

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Macquarie Island (34 km long x 5 km wide) is an oceanic island in the Southern Ocean, lying 1,500 km south-east of Tasmania and approximately halfway between Australia and the Antarctic continent. The island is the exposed crest of the undersea Macquarie Ridge, raised to its present position where the Indo-Australian tectonic plate meets the Pacific plate.

It is a site of major geoconservation significance, being the only place on earth where rocks from the earth’s mantle (6 km below the ocean floor) are being actively exposed above sea-level. These unique exposures include excellent examples of pillow basalts and other extrusive rocks.

Macquarie Island is an oceanic island in the Southern Ocean, lying 1,500 km south-east of Tasmania and approximately halfway between Australia and the Antarctic continent. The island is the exposed crest of the undersea Macquarie Ridge, raised to its present position where the Indo-Australian tectonic plate meets the Pacific plate. It is a site of major geo-conservation significance, being the only place where rocks from the Earth’s mantle (6 km below the ocean floor) are being actively exposed above sea level.

It is the only island on the planet composed entirely of oceanic crust and rocks from the Earth’s mantle deep below the surface.

Macquarie Island probably began as a spreading ridge under the sea with the formation of new oceanic crust somewhere within 11 million and 30 million years ago.

At some stage the spreading halted and the crust began to compress, squeezing rocks upward from deep within the mantle. As the ridge grew it eventually became exposed above the ocean surface about 600,000 years ago. Thus, rocks normally only occurring deep within the Earth’s mantle have become exposed on the surface.

Since Macquarie Island emerged, it has mainly been carved by marine processes such as wave action, unlike other subantarctic islands, which have been shaped by glaciers.

These unique exposures include excellent examples of pillow basalts and other extrusive rocks.

The main landscape feature is a central rolling plateau 250-300 m above sea level, bounded on all sides by steep cliffs, from the foot of which extends a coastal platform up to 800 m wide. Glacial drift up to 20 m thick covers much of the plateau and there are some lakes.

One of the most aesthetically appealing sights of the island are the vast congregations of wildlife, particularly penguins, on suitable parts of the coastal terrace, especially during breeding seasons.

During the breeding season on suitable beaches elephant seals also form impressive colonies. Four species of albatross nest on steep and rugged cliffs, both on the main island and on nearby Bishop and Clerk Islands.

The terrestrial area of Macquarie Island is a State Reserve with protection extending to low water mark. The marine values are safe by the Macquarie Island Marine Park declared by the Commonwealth on 28 October 1999. The main function of the marine park is to protect the conservation values of the region from human disturbance. The marine park contains the world’s largest marine highly protected zone, covering more than 16 million hectares.

Sealers discovered the island in 1810 and inhabited it periodically through the 19th century, exterminating the fur seals and greatly reducing the elephant seal population. In 1870, gangs came to exploit the king and royal penguin populations for oil, eliminating the former. The original elephant seal population of about 100,000 animals was reduced by 70% as a result of these operations. The visitors also brought exotic mammals and caused the extermination of two endemic subspecies of land birds.

There are no permanent human inhabitants on Macquarie Island even though Australian Antarctic Division station is occupied all year long. The only access to the island is by sea and there are no harbors or landing facilities, so ship-traffic in the location is minimal.