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Christmas Island - Geography

Christmas Island is located in the Indian Ocean at latitude 10°30‘ south and longitude 105°40' east. The Island is the summit of a submarine mountain. It rises steeply to a central plateau dominated by rainforest. The plateau reaches heights of up to 360 meters and consists mainly of limestone with layers of volcanic rock.

The Island's 80 kilometer coastline is an almost continuous sea cliff reaching heights of up to 20 metres. There are thirteen places where breaks in the cliff give way to shallow bays and small sand and coral beaches. The largest of these bays forms the Island's port at Flying Fish Cove. The Island is Point (see Map), about nine miles; the least on a line drawn north and south through Murray Hill, about three and a half miles. The total area of the island may be roughly stated as 43 square miles.

If the coast be examined in a boat, or from the edge of the sea cliff, it is found that round the greater part of the island there is a submarine terrace or shelf, which varies greatly in width and in its depth beneath the surface. At Flying Fish Cove this terrace consists of two portions—an inner, which is partly dry at lowwater, and outside this and about two fathoms below it, a second, which slopes away seaward to about 20-30 fathoms, beyond which the water deepens suddenly. The upper reef is best developed at the northern and southern ends of the cove, and is almost absent in the middle. It exactly resembles the reef flat of an atoll. At low-water it can be seen to be composed of blocks of coral cemented together and forming a smooth, hard surface, like concrete, bored in all directions by marine worms. Some of the individual corul masses surrounded by a coral reef. There is virtually no coastal shelf and the sea plummets to a depth of about 5000 meters within 200 meters of the shore.

The island consists of a central plateau, highest towards the north and cast, and descending to the sea on all sides by a succession of terraces, separated by slopes or cliffs. In most places the arrangemeut of these, from the edge of the plateau downwards, is — (1) a steep slope strewn with blocks; (2) a broad terrace, followed by a similar slope (this seems to be wanting on the south); (3) a second terrace, terminating in a cliff 200 or 300 feet high; (4) the shore terrace, sloping gently down to the sea cliff; (5) the present fringing reef. There are, however, many local differences.

The greatest length of the island is from North-East Point to Egeriu Point, a distance of about 12 miles. The greatest width is from North-East Point to Southare of considerable size, and the section of one spherical mass was about four feet in diameter. On the surface of the reef are numerous loose blocks and large plate-like masses of coral, and towards the beach are a number of enormous masses of white foraminiferal limestone.

Nearly the whole of the coastline is formed by limestone cliffs, varying in height from about 15 to 150 feet or more. The latter height only occurs at Steep Point, in consequence of certain movements which will be described elsewhere; in other places tri" height seldom exceeds 50 feet. The cliff's are nearly everywhere much undercut, and sometimes overhang to the extent of 30 feet or more. There are numerous caves, and occasionally these have openings on the shore terrace at some distance from the sea.

When a heavy sea strikes the cliffs, the air is driven through these passages with great violence, and sometimes accompanied by a column of spray 60 or 70 feet high. These hlowholes are most numerous on the south coast, where the cliffs are exposed to the heavy ocean swell caused by the south-east trade-wind, which prevails during the greater part of the year.

Speaking generally, the whole of the upper part of the island consists of a plain, sloping gently to the south and west, and possessing a surface varied with shallow valleys, rounded flattopped hills, and low ridges and reefs of coral limestone. On the northern and eastern sides the edge forms, in most places, a raised rim, bounded externally by a low cliff, below which comes the uppermost of the inland cliffs above described. In other places it passes into the inland cliff by a more gentle slope. The actual margin is usually marked by a belt of limestone pinnacles of greater or less width. Another notable feature is the occurrence on the northern and eastern borders of several peculiar hills, the long axis of which lies parallel to the edge of the plateau.

The distribution of plants on the island is related to soil depth moisture retention as well as exposure to and distance from the sea. A dense rainforest has evolved in the deep soils of the plateau and on some terraces. The forests are dominated by several tree species. Ferns, orchids and vines flourish on the branches in the humid atmosphere beneath the canopy.

Christmas Island National Park covers approximately 63 per cent of the Island and contains large tracts of tall rainforest, beaches, caves, freshwater streams and waterfalls as well as rare plants, bird life and other wildlife. A Visitor's Centre is operated by Parks Australia at Drumsite where advice on plants, wildlife and sightseeing is provided. The park is accessible by road and there are many walks along boardwalks or tracks. Guided tours are also available.

Spectacular fish, corals, rock formations and caves provide exciting snorkelling and diving opportunities on Christmas Island, from both the shore and by charter boat. The famous migration of large numbers of red crabs occurs between October and January each year. Whale sharks are also seen at this time. There are many vantage points to watch birds, some unique to Christmas Island, such as the Christmas Island Frigate Bird and the majestic Golden Bosun.





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Page last modified: 26-07-2017 19:17:10 ZULU