The Drakensberg - Soul of the Zulu Kingdom

The Geology or Geological Formation of the Drakensberg

The imposing Drakensberg escarpment as we know it is the product of millions of years of sculpting by the elements. The foundations of the mountain range reach back billions of years. Its formation provides a fascinating story, and its imposing rock walls and deep, green valleys have provided a home for an ever-changing variety of life through the ages.

zoom Rockeries Pinnacles, carved from Basalt, Mnweni area Photo: R.Biggs

Eons before the first lavas began to flow in the area of the present- day mountain range we call the Drakensberg, the place was part of a shallow depression fed by inland waterways. It was an enormous inland lake, the waters of which floated upon a vast area of an ancient land mass called Gondwanaland. This supercontinent included Africa, Australia, New Zealand, South America and Antarctica. The sediments carried into the lake were gently deposited upon granite foundations which had formed almost three billion years ago. Today, in areas such as Wit Umfolozi, Old Baldy in Valley of 1000 Hills and Kloof Gorge, small portions of these grandfather granites are exposed giving visual evidence of the ancestry of the landforms. These oldest of rocks are exposed nearest the coast where the elements have worked hardest to reveal their secrets.

The sediments of mud and sand were deposited for millions of years into the vast central swamp - a place where dinosaurs lived and died. They became agglomerated and compacted through the immense pressure caused by the weight of all the overlying layers. This thick blanket of sediment built up about 490 million years ago and today the resultant sandstone can be seen forming the typical table- top shapes in the Valley of 1000 Hills and around Oribi Gorge near Port Shepstone.

Through the next 250 million years, several more thick layers of sediment were deposited into the swampy depression. These sediments resulted in the formation of red, green and purple- coloured mudstones that contain rich fossil deposits of both carnivore and herbivore reptiles and of the vegetation they fed upon. However, during the deposition of what is known as the Beaufort Series of sandstones, life on earth all but disappeared. Fossil evidence shows that more than 90% of known species became extinct, but no one really knows why.

The next layer of sediments deposited over the Beaufort sandstones built up the blue and grey Molteno and red coloured Elliot formations about 200 million years ago. These form the small cliffs in the foothills of the Drakensberg. The layer is easily recognised due to the way it sparkles in the sun. The glistening is due to tiny quartz crystals, which form a cement between the sand grains. It was also the even Molteno layers that the Bushmen were to use as canvas for their art and even later was to be used by farmers to build their houses.

These layers also contain early dinosaur fossils. The footprints of these early creatures can be found in the sandstone caves of the Drakensberg foothills, often exposed on the ceilings where the softer sediment layers below them have been worn away.

Towards the end of the period during which these sandstones were deposited, a long period of desication occurred with the deposition being caused no longer by rivers, but by wind in a desert environment. These wind-blown deposits formed the Cave Sandstone and built up the massive sandstone cliffs which today run along the entire length of the Drakensberg sometimes reaching heights of 200 metres.

zoom Geological Structure of the berg Source: R.Porter

It was on top of these deposits that the Drakensberg mountain range was to grow, and it was partly the immense weight of all the sediments, which contributed to the massive breaking up of the landmass which occurred.

Some 160 million years ago, enormous internal pressures contributed to the cracking apart, breaking up and drifting away of the continents which once constituted Gondwanaland. This movement also resulted in enormous cracks in the crust of the African continent and it was through a series of these cracks or fissures that the massive lava flows which were to create the Drakensberg began. This was volcanic activity, but it was not of the explosive kind. Rather, the thick lavas flowed and cooled, flowed and cooled, adding from 30 cms to 50 metres of lava at a time from the fissures which occurred roughly where Lesotho is today. Throughout 20 million years these flows built up a deposit of basaltic rock over 1,5 kilometres thick in some places and covered an area extending from inland of present day Lesotho over most of KwaZulu-Natal as far as Mozambique and the Indian Ocean.

The basaltic lavas were far from solid, being riddles with holes from trapped gas bubbles and tubes where the hot bubbles escaped upwards. Later these spaces were filled with white zeolite minerals, resulting in the white inclusions called amygdales, some of which are the beautiful blue, grey and white agates, chalcedony and quartz crystals which delight rock collectors and reward sharp-eyed hikers. In the lower reaches, amonites existed at the same time as the mountain dinosaurs and both faced the same fate when, about 65 million years ago, a large meteorite impact contributed to their extinction.

At the same time as the fissure flows were adding a massive cap over the softer sandstones and shales, other flows which could not reach the surface were being forced into underground cracks and crevices. Unlike the brittle basalts of the cap layers these underground lavas formed hard blue dolerite dykes and sills throughout the area. The resistant horizontal sills resulted in time if the formation of land forms, usually waterfalls, such as Howick Falls.

In some places the doleritic dykes have eroded much faster than the surrounding rock, as is the case in the high Berg where it is surrounded by basalt, and this process created the Crack in the Royal Natal National Park area, and the pass at Bannermans Pass in the Giants area of the Drakensberg, amongst other features.

Once the massive flows of basalt lavas had cooled they were immediately exposed to the erosive forces of wind, rain, ice, lightning, heat and drought. Where the elements broke through the basalt cap into softer layers, erosion was faster and caused steep sided valleys with churning rivers tumbling seawards. The erosion backwards to the present-day escarpment was a relatively rapid process - about 200 kms in 140 million years, or an average of 1,42 mm per year. Even so the Drakensberg lavas are resistant to erosion and form the high peaks of the escarpment as well as the protective capping of the little Berg.

zoom Mountain Rescue Teams, Drakensberg Photo: Mervyn Gans

The lava flows ceased about 140 million years ago and since then no more building up has occurred. Instead of deposition, erosion became the dominant force in the mountain paradise, forming the imposing peaks and steep sided valleys we know today. The high peaks and vertical walls were to issue an irresistible challenge to mountaineers, just as the hills and valleys would call to hikers, rewarding their efforts with opportunities to swim in clear icy pools and shower beneath refreshing waterfalls. Much was still to happen in these mountains before that time came to pass.

The geological formation of the Drakensberg continued ....

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