Masses of water cascade over the imposing rocky edge, thundering 65m to the depths below. While the waterfall is the major attraction at the Augrabies Falls National Park, it is one of many geological features in this protected area that tell the story of the tumultuous past of this awe-inspiring landscape.
Once, volcanic activity ripped and shape the seemingly unbendable rocks, a rich marine life flourished and rocks tore apart to bend and force the landscape into being.
The famous falls were formed about 1.8 million years ago, progressively cutting back eastwards along faults in the pink gneiss. This is a widespread rock-type formed by the metamorphosis of granite due to extreme heat. You can often see layers of coarse mineral grains in it. From the falls the Orange River flows into a deep, 100 metre wide gorge which extends 18 km. The formation of the gorge and the evolution of the falls are associated with the continental uplift during the late Tertiary, a period 66 million to 2.58 million years ago, roundabout when Gondwana finally split apart. Ararat and Oranjekom viewpoints offer spectacular views overlooking the gorge.
Another distinctive landmark in the central area of the park are the Swart Rante, black hills that loom razor sharp on the horizon. These form a divide between a harsh environment that spans towards the gorge on the one side, and fertile soil on the other. The imposing hills are built from Metagabbro, a rock that formed when lava cooled and solidified and later metamorphosed. It contains no quartz and is made up entirely of dark ferromagnesian minerals and feldspar.
Moon Rock, a large granite rock dome is a prominent feature, and the moonlike round surface was once molten lava that set and retained its shape after the softer rock surrounding it weathered away. This ‘moon’ is scattered with ‘pop ups’ – thin slabs of rock that detached from the rock surface due to extreme changes in the rock, pop up, and lean against another thin slab, forming an ‘A-tent’ shape.
Different weathering patterns can be seen in the park, such as hollows in the rock, exfoliation domes, and Kobus van Coppenhagen is passionate about the geology of the area and says that the western side of the park is an even bigger gem. The Nama Plateau was formed because of high grade metamorphic processes. This happens when temperatures are greater than 320 degrees combined with relatively high pressure. Today Spieëlkop in the Blouputs area, the highest point in the park at 904 m, is the best-preserved remnants of this plateau south of the Orange River.
This plateau is the floor of what was once a shallow sea, and the fossils of the rich marine live that thrived here 540 million years ago were once discovered here.
Also in the western section, far away from the existing riverbed, you will find potholes, cavities in the rock caused by turbulent water. They were formed more than 30 million years ago and proves that water played an important role in establishing the terrain. These formations are unfortunately not accessible to park visitors, but can be seen from a viewpoint on the neighbouring Daberas farm.
There is another visible formation that spans across the entire length of the park and all the way to Upington, a 130km long dolerite dyke. Dykes form when hot magma pushes up through cracks in the earth’s surface. This one can be seen from aerial photographs and Google Earth. It runs from west to east next to the river.
The oldest rock formations are found in the north of the park in the Melkbosrand area owned by the Riemvasmaak community. They are called “kinzigites”, or metapelites (high grade metamorphic mudstone). These rocks are rich in minerals like Iceland spar (pure form of calcite), quartz crystals, fluorite and amethyst. The presence of hot springs at Riemvasmaak are proof that joints in the earth’s crust provide a deep circulation of groundwater resurfacing as hot mineralized water. The water away from the river is brackish.
Van Coppenhagen reiterates the importance to preserve all the formations. There will never be duplications if they are destroyed. “With plants and animals you could relocate and breed to restock an area with specimens, but with iconic geological features you have to be much more careful.” If you remove a rock to inspect it, make sure you return it like you found it and not upside down. This changes the landscape.
Read about the geology of the central section in Augrabies Splendour/Weelde (Prof P. van der Walt) and Geological Journeys (N. Norman and G. Whitfield).
Photographs taken by Petro Kotzé
Content courtesy of SANParks Times: www.sanparkstimes.co.za