A rocky outcrop, set in an upland hollow, glistens in the morning light. The depression, enclosed by steep slopes, hides the wider setting. But just a stone's throw away is a wide open, exhilarating scene. Beyond a ridge landscapes and seascapes spread out: the vista reveals hills and ridges, ravines and valleys, bays and islands, cliffs and long promontories.
Exploring Hong Kong walkers delight in its complex, surprising topography. There are rugged uplands, sheltered lowlands, and a coastline of extraordinary intricacy. Amidst this beauty are hiking trails that, reflecting the land itself, vary from pleasant to challenging. Yet few people appreciate how beautiful is the landscape - or how long ago the natural setting was formed.
Geologically and climatically, Hong Kong is part of South China. Situated just east of the Pearl River estuary, its landforms are an extension of Guangdong's - with the province's most indented coastline. Including reclamations, Hong Kong's land covers about 1,090 square kilometres; and within this small area there are numerous landforms and great natural diversity.
The summits rise to over 500 metres, and the highest peaks reach over 900 metres. There are only a few small upland plateaus, and the mountains mostly drop down steeply to confined valleys. Countless hillside streams plunge through ravines. In the wet summers they can be torrents, but during winters most of them barely run. There are few major lowland streams and Hong Kong has no proper river.
Isolated lowlands lie scattered between the ranges. Most are small valleys that nestle beneath steep slopes or lie behind coastal bays. Only in the northwest is there any extensive flat land: there a wide alluvial plain spreads out between Hong Kong's highest mountain and the sea. Around the coastline there is generally very little flat land - and often there is none at all.
The coastline, including some 260 islands and islets, extends for about 800 kilometres. In the east there are numerous cliffs and caves, coves and inlets; while in the west the coast is generally gentler, with long beaches and wide bays. An arc of islands, some 60 kilometres long, adds to the coastal charms - with treacherous crags, tiny islets and precipitous islands.
The geology of Hong Kong is varied. Volcanic rocks underlie almost half the area, granite rocks underlie a third, and sedimentary rocks make up only a small fraction. The main ridges and valleys are aligned northeast to southwest, while some lesser features lie northwest to southeast along the geological grain. The eastern half of the territory has the steepest, most rugged landscapes, with narrow valleys and a cliffed coastline. The western half has more rounded slopes, large areas of flat land, and a lower-lying coastline. How and when did these features originate?
Hong Kong's oldest rocks were laid down in the Devonian Period, 400 to 360 million years ago. First deposited as sands on the flood plain and in the channels below an ancient mountain range, the material was later compressed into sedimentary conglomerates, sandstones and mudstones.
Standing on the coast today it is hard to comprehend the massive fluctuations in sea levels that have been part of the story of land formation. But the fact is - from the early Carboniferous Period through to the early Jurassic, no less than 170 million years, the Hong Kong region was submerged beneath the sea.
In early Carboniferous times (some 340 million years ago) the local seas were shallow, and coastal swamps later replaced them. Limestone formed under the seas, coal in the swamps - which were later transformed into, respectively, marble and schists. Still deeper seas covered the area in the early Jurassic. Silts settled to form siltstones and sandstones, which held the fossils of ammonites, primitive life forms.
For some 20 million years, from the Jurassic to the early Cretaceous (165 to 142 million years ago), Hong Kong was located on a chain of volcanoes along the coast of China. Molten rock erupted explosively. Minute ash particles settled to form a rock called tuff. Other magma, cooling slowly below the surface, formed today's granite.
From 100 to 80 million years ago there were bare rocky mountains, wide flat valleys, seasonal streams, and sparse vegetation. The subsequent 30 million years were wetter, with the beginnings of a seasonal climate and shallow lakes. In the first period conglomerates and sandstones formed; and in the latter silts that held the remains of early plants.
A gradual wearing down of the earlier rocks occurred during the last 60 million years. Slowly our modern landscape appeared: mountains took on distinct shapes, valleys widened, and limited alluvial plains formed. By the start of the Quaternary Period, two million years ago, the topography was largely as we see it today - though the seas were lower.
In the last two million years sea levels have varied by as much as 150 metres, during the glacial periods. At the height of the last glacial period, about 16,000 BC, the sea level was 130 metres lower than today, and the regions' streams joined to form rivers which flowed southwards for about 120 kilometres to the ocean. Then, from about 15,000 to 5000 BC, the climate warmed. As the ice sheets melted the sea rose. Valleys became bays, ridges became headlands, and peaks became islands. Gradually, beaches formed along the new shoreline.
The global climate stabilised about 5000 BC. Even before then, the alternate heating and cooling of the Asian continent was the main force controlling Hong Kong's climate. Today, as for past millennia, in winter the continental northeast monsoon brings dry, chilly and even cold weather to Hong Kong; and in summer the oceanic southwest monsoon brings tropical heat, humidity and intense rainfall. Warm temperatures, heavy rain and typhoons contribute to weathering, landslips and coastal erosion.
Unweathered granite has joints that allow penetration by water, together with the natural acids that rain absorbs. The penetrating water gradually weathers the granite - then loose surface material slowly erodes away, leaving large boulders or corestones on the slopes. The water saturation of weathered rocks on steep hillsides can lead to instability, and landslides occur when this happens.
Around the coast the primary erosive force is the explosive power of storm-driven waves. Along the eastern coastline crashing swells have cut the rock into cliffs, platforms, caverns and sea arches. Around the western coasts the Pearl River estuary is the main influence. There, over countless centuries, the river has deposited vast volumes of silt, steadily rounding off the coastline and making the bays and channels ever more shallow.
The story of Hong Kong's land formation and its geology is best told 'in the field'. Take a copy of Hong Kong Rocks, a well-illustrated field guide, and go exploring. Study the rock faces in the country parks; examine the hillside boulders with their joints. And explore the coast, where almost everywhere wonderfully coloured and textured rocks lie waiting.
The next activity allows you to integrate your map reading skills with information from the Stokes reading in order to summarize and analyse the key landscape features in Hong Kong.
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