The Sphinx EarthCache
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The Sphinx is an interesting rock formation in the Drakensberg, which when viewed from a distance looks like the Sphinx in Egypt.
Access is via the walking trails from some of the hotels in the area, or from the nearby Monk's Cowl Nature Reserve.
The trail is well signposted, and we hope you enjoy your walk as much as we did.
In order to substantiate your visit and be able to log this EarthCache, a number of questions need to be answered and submitted to the cache owner via e-mail.
Geology of the Drakensberg
The geology of the Drakensberg consists of igneous and sedimentary rocks, which in this area usually lie horizontally.
Igneous rocks (derived from the Latin word ignis meaning fire) are formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface as intrusive rocks or on the surface as extrusive rocks.
Sedimentary rocks are formed by the depositing of material at the Earth's surface and within bodies of water. Sedimentation is the processes that cause mineral and/or organic particles to settle and accumulate or when minerals precipitate from a solution.
The Drakensberg escarpment is the product of millions of years of sculpting by the elements. 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, which included what is now 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. They became compacted through the immense pressure caused by the weight of all the overlying layers. This thick blanket of sediment built up over 490 million years.
Through the next 250 million years, several more thick layers of sediment were deposited into the swampy depression. These sediments(known as the Beaufort Series of sandstones) 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.
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. 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 desiccation 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.
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 180 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.
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.
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.
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.
Logging this EarthCache
To log this EarthCache, please answer these questions:
- Describe the layers of rock that make up the Sphinx. What colours are they, and what type of rocks are they likely to be?
- Standing at S29 03.347 E29 23.888 there are some interesting erosion patterns developing on the rock face in front of you. Describe the type of erosion that you see, as well as what you believe is causing this to happen.
- Also walking along the path around S29 03.347 E29 23.888 there are noticeable differences in the rocks that make up the path. Compare these to the rocks you can see in 1. and comment on the texture and colour and makeup of the rocks now that they form part of a path that has regular traffic along it. How does this differ from the rocks next to the path.
- Optional, post some photos of your visit and the views you get to enjoy.
PLEASE NOTE: You may log your visit prior to approval, but you must still submit your answers, logs that do not meet the above criteria will be deleted.
References:
http://www.zulu.org.za
http://en.wikipedia.org
Additional Hints
(Decrypt)
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