ENG-1994 — Page 492

THE ENVIRONMENT

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Royal Observatory, the highest for any three consecutive days in July. A Rainstorm Black Warning was issued on July 23. Among many reported incidents, the most disastrous involved the collapse of a retaining wall at Kwun Lung Lau Estate in Kennedy Town, killing five people, injuring three others and requiring the evacuation of two thousand families.

The wet conditions continued into August. However, Harry was the only tropical cyclone in the month that necessitated the hoisting of local tropical cyclone warning signals.

September was more humid and cloudier than normal. There were only 124.8 hours of bright sunshine

the second lowest on record for September. The total rainfall of 298.9 millimetres was near the September average of 299.7 millimetres.

Under the influence of persistent northeast monsoons, October was a fine and dry month. The mean cloud amount was only 36 per cent - 20 per cent below the October normal.

In the absence of significant surges of the winter monsoon, November was much warmer than usual. The mean minimum temperature of 21.1°C and the mean temperature of 22.9°C were the highest and the second highest, respectively, on record for November. The month was also relatively humid, but the weather was generally fine with little rain.

December was mild and humid. The mean temperature of 19.8°C and the mean dew-point temperature of 16.4°C were both the second highest on record for December. It was also very cloudy, with total bright sunshine amounting to only 70.2 hours the lowest December record. Heavy rain fell on December 8 and necessitated the issuance of a flood warning for the first time in December, a normally dry month.

Topography and Geology

Hong Kong's natural terrain is dominated by mountains and hills with steep slopes, many of which descend sharply into the sea. Offshore, the seabed is relatively flat, sloping gently towards the south. The highest points in Hong Kong are Tai Mo Shan in the New Territories (957 metres) and Lantau Peak (933 metres). The deepest point is in the Lo Chau Mun (Beaufort Channel) north of Po Toi Island, in which a sounding of 66 metres is shown on the Admiralty chart. Other deep areas are in Kap Shui Mun and the Ma Wan Channel, between Lantau and Tsing Yi islands.

The mountains are composed primarily of volcanic rocks, with some of the lower hills formed of granite. Low-lying areas tend to be underlain by granite or sedimentary rocks. In places, hillslope debris forms a mantle over the bedrock and alluvium fills some of the valleys overlying bedrock. Offshore, the deepest areas are usually scoured by currents and bedrock is exposed. Much of the remainder of the seabed is covered by marine mud with scattered sand banks, though many of these have recently been removed as fill for reclama- tion projects.

The territory lies on the southern edge of the ancient Sinian land mass, formed more than 600 million years ago. The oldest exposed rocks are Devonian sediments which were deposited 300 million years ago, possibly by a river draining the land mass to the north and feeding a delta to the south. The area was subsequently inundated by the sea and shallow marine sediments were deposited, represented by the Carboniferous marble of Yuen Long and Ma On Shan and the sandy and muddy sediments of the Permian rocks of Tolo Harbour. During the Jurassic and Cretaceous periods, 170 to 135 million years ago, while dinosaurs roamed the land to the north, Hong Kong was the scene of violent volcanic activity, with lava and volcanic ash being deposited over the territory. The eruptions were associated with