THE ENVIRONMENT
October was the fifth-wettest on record. Daily rainfall exceeded 100 millimetres on three days during the first week. The total monthly rainfall of 476.9 millimetres was more than three times the normal figure. Typhoon Sibyl came close to Hong Kong in the beginning of the month, necessitating the hoisting of Tropical Cyclone Warning Signal No. 8.
November was dry, with only 1.8 millimetres of rainfall recorded against a normal of 35.1 millimetres. The relative humidity dropped to 17 per cent on November 24, the lowest on record for November. Fire Danger Warnings were issued for 19 days in the month. About 160 cases of hill fire were reported on November 1.
With the prevalence of the winter monsoon, December was generally fine and dry. Fire Danger Warnings were issued for 18 days in the month. Frost was reported at the Sha Tin Racecourse on the morning of December 31.
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. 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, where the Admiralty chart shows a sounding of 66 metres. Other deep areas are in Kap Shui Mun and the Ma Wan Channel, between Lantau and Tsing Yi islands.
The mountains consist 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 reclamation 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 deposited 375 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 experienced violent volcanic activity with lava and volcanic ash being deposited over the territory. The eruptions were associated with the development of giant craters. At the end of each main phase of volcanic activity, these craters collapsed to form calderas and the lava and ash pile was intruded by magma, which slowly crystallised to form granite.
During the Tertiary period, 60 million years ago, the area became less active, though the environment was still quite hostile. Rocks now seen on the island of Ping Chau represent sediments laid down in a temporary lake on the edge of a desert extending to the north.
During the Quaternary period, spanning the last two million years, major glaciations in polar regions affected the global sea level, which fell to 120 metres
387