ENG-1993 — Page 466

THE ENVIRONMENT

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volcanic in origin and about 20 per cent is granitic, while slope deposits cover 15 per cent. A further 20 per cent is alluvial in nature, while about five per cent of the land is currently formed by reclamation and fill.

The highest peak is Tai Mo Shan (957 metres), located in the central New Territories. Four other peaks exceed 750 metres, all on Lantau Island. Victoria Peak, the highest on Hong Kong Island and best known as a major tourist attraction, is ranked 18th in the territory with an elevation of 554 metres.

The territory lies on the edge of the ancient Sinian land mass formed more than 600 million years ago, and which now extends from Shandong in northern China to the Gulf of Hainan. The oldest geological strata forming Hong Kong's land mass were deposited beneath the sea but were subsequently folded and faulted in mountain-building earth movements. A second period of mountain-building, beginning about 160 million years ago, was accompanied by explosive volcanic activity which deposited thick layers of ash and lava. Large granitic intrusions accompanied this volcanism, which lasted up to about 136 million years ago. These mountains were subsequently eroded, and the material washed from the slopes into the valleys, plains and shallow seas formed flat-lying sedimentary rocks and soft sediment deposits.

During the Quaternary period of the last 1.6 million years, world sea levels fell and rose several times. There were four major glaciations when water was taken up to form great ice sheets. In Southeast Asia, the sea level fell to between 120-150 metres below its present level, which would have exposed an area of continental shelf about 130 kilometres wide to the south of Hong Kong. During these low sea-level periods, the Pearl River deposited alluvial sand and silt over this wide plain. As the ice began to melt at the end of the last glaciation, sea levels rose, reaching their present level about 6 000 years ago. The returning sea deposited fine clays and silts (marine mud) over the earlier alluvial deposits. Sea level fluctuations during the Quaternary have therefore resulted in a sequence of mud, sand and gravel up to 100 metres thick in the present offshore area.

The erosion of the hills accelerated following destruction of the natural vegetation during the widespread colonisation of the area in the Sung Dynasty (960–1279). Hong Kong's rocks are generally deeply weathered, and much of the terrain is prone to landslips. More than 20 per cent of the terrain in the territory shows evidence of instability.

Generally, the weathered granitic and volcanic rocks can be excavated quite easily for use as reclamation material. However, sand dredged from offshore areas provides the most valuable fill resource. Hong Kong has few mineral resources, although iron and tungsten were once extracted in significant amounts, and deposits of lead, silver, zinc, quartz, kaolin, beryl and graphite have been mined in small quantities. Granites in Hong Kong were once extensively quarried for masonry, but are now mainly used as aggregates.

The natural landscape in the urban areas has been extensively modified as a result of site formation associated with development. Many of the natural granitic hills have been removed, and the material used as fill for the various reclamations. Almost 4 000 hectares of the developed land is reclamation.

Much of the undeveloped terrain in Hong Kong consists of steeply-sloping ground where soils are thin and nutrient-deficient. These soils support only grassland or shrubland, except in protected valleys where small areas of broad leaf woodland survive, or in water catchments and country parks where re-afforestation has succeeded in establishing pines and deciduous trees.