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NAMIBIA Jenny Martin In July and August 2005 we went on a train safari to Namibia. As Namibia is four times the area of Germany, this was an excellent way of seeing the country. The scenery is fascinating, the minerals very varied, the wildlife wonderful and the geology amazing. This is just a snippet of what we saw. The rocks vary in age from more than 2000 million years old, in the remnants of the Vaalian mountains that arose when land was added to the Congo craton, still visible in the North West, to the very recent extension of the dune belt along the coast from Walvis Bay to Swakopmund caused by the sparse rainfall allowing the barchan dunes to cross the delta area of the Kuiseb river. The first place we visited was Fish River Canyon, photograph 1. This is second in size only to the Grand Canyon at 90km long, more than 20km across and 549m deep at its deepest. evidence in the area now. When Gondwana began to break up at about 120ma, the Atlantic ocean opened pretty well along the present day coast, the edges of the African continent lifted, due to equalisation and the gradient of the river was greatly increased and began to cut down within its existing bed through the Nama group into the metamorphic rocks below. With the current climate the river only flows intermittently in the rainy season.We walked about 3 kms along the Canyon rim marvelling at the view of meanders and islands, also enjoying the birds and flowers. We were lucky as there had been some rain in the previous fortnight so, although it was winter, we saw Namaqualand daisies, desert roses and many more varieties that we did not know. Back to the train for a BBQ then we travelled on to Aus for the night. On the way we had to climb up from the Fish river gorge on to the plateau, a circuitous route crossing dry riverbeds and gradually rising through the rock layers. There were baboons and gemsbok and, at one point, we were allowed to get off to take a photo of the train in the gorge! Next morning we boarded coaches to descend from the plateau to cross the stone desert to Luderitz, photograph 2. Photograph 1: Fish River Canyon The lowest rocks are the roots of the Namaqualand Metamorphic Complex mountains of 1500ma (million years old) and are gneisses. 800ma dolerite dykes were intruded. Erosion continued until 650ma when there was a marine transgression laying down horizontal layers of sandstones, (later to become quartzites) and conglomerates first, then black limestones and mudstones (later to become schists); these are the Nama Group sediments. After the sea dried, about 550ma, once again there was a gap. 350ma a tectonic event activated faults and a graben was formed and it is within this graben structure the Fish river flows. Originally the gradient was shallow and most of the erosion was sideways producing a riverbed with meanders and cut-offs. At this time Namibia was part of Gondwana and as the continent got closer to the South Pole the area was affected by the Gondwana Glaciation; the canyon was filled by ice and further eroded, although there is no visible 26 Photograph 2: Luderitz At first there was quite a lot of feathery grass; this has deep fleshy roots to survive the lack of rain. Here there were ostriches, gemsbok and a herd of horses that have managed to adapt to the conditions after being abandoned in the First World War! As we got towards the coast, the bushes of Ostrich grass died out and there was nothing except sand and stone with a few low granite hills against which the sand had piled. Right down at the coast the old railway running alongside was buried in places by Barchan dunes; these are the wandering dunes that move along in the wind. Sometimes the road gets blocked but not while we were there. We finally dropped to the coast between amazingly Journal of the Bath Geological Society, No. 25, 2006 convoluted rocks, once again the Namaqualand Metamorphic complex, but this time black and grey dolerite, anatexite, gneiss, amphibolite and pink granite. Out on the peninsula it is just a rock desert with flamingos, cormorants, gulls and fur seals. Luderitz itself is very interesting with old (1906!) German houses and the Church on the Rocks overlooking the harbour. We drove out onto Shark Island and looked across to the Dune Sea sand hills as high as the coastal mountains - that extend from Luderitz to Walvis Bay. The sand sea is a consequence of the arid climate and the prevailing wind. The cold Benguela Current cools the South Westerly wind which is pushed under the warm inland air masses so that no rain clouds form. The sand comes up the coast from South Africa, the product of erosion in central Africa washed down the Orange River, deposited on the coast and blown inland. On our way back to the train we visited the deserted town of Kolmanskuppe, once an extremely prosperous diamond town; and also the First World War German POW camp at Aus. I will skip our visit to Windhoek except to mention the descent into the graben structure in which it is situated between the Khomas Hochland mountains to the West, which are mica schist, and the Auas mountains to the East, which are quartzite. Both these ranges are the eroded remains of the Damara Mountain Building event formed from 750ma to 650ma when the Kalahari and Congo Cratons joined, closing the sea between them and adding to the eventual Gondwana continent. Our next stop was Tsumeb in the Otavi mountains, which are well known for the lead-zinc-copper deposits, and 226 different minerals have been found. The Tsumeb ore deposit is a hydrothermal event in an ancient dolomite pipe that was progressively filled with breccia and sand during the closing of the sea between the Congo and Kalahari cratons before the mountain building and associated magmatic activity caused the mineralisation.Unfortunately we only had time to drive round the town as we were visiting Etosha National Park. The Etosha NP is in the Ovambo Basin, which was the foreland of the Damara mountains and collected erosional materials. Later a glacier in the Gondwana Ice Age scoured the depression and later again it became a desert with dune sand that became consolidated as the Etjo sandstone. After the break up of Gondwana and the uplift of the earth’s crust, it became the recipient of river erosion debris from the carbonate mountains of Angola, a huge lake formed with only the Kunene river to partially drain to the sea. Consequently, as the climate warmed, the lake shrank and left salt crust behind. The Etosha Saltpan makes an excellent place for viewing game, particularly on its Southern edge where there are springs caused by the meeting of the Karst Otavi mountain rocks with the clays of the saltpan. We saw desert elephants, giraffe, zebra, gemsbok, springbok, wildebeest, dikdik, impala, jackals, yellow and red hornbills, Koori(!) bustards, ostriches, bateleur eagles, louries, eland, hartebeest, vultures, secretary birds, duiker, Cape starling, goshawks, steenbok and wart hogs. The saltpan looked blue/green from a distance but grey up close. There were dust devils and mirages; altogether a memorable visit. On our way back to the train we visited another fascinating place. Otjikoto Lake is a very deep, almost round pool of blue/green water set in white limestone cliffs. It is where the roof of a cavern has fallen in; there is another fairly nearby, and they are part of an underground system in the very old (700ma) underlying dolomite rocks. The water was sometimes still and then the surface would be disturbed by up-welling from below and set up overlapping ripple patterns before becoming calm again. Looking down one could see fish, tilapia and something smaller in the water. It is a bit commercialised and I bought some tourmaline and beryl from the mines. Next morning I woke to find we were passing the cliffs of the Erongo volcano. The upper layers are ignimbrite over ash and lava, these on top of Karoo sediments, with granite exposed around the bottom. It looked magnificent in the pink dawn light. We were on our way to Swakopmund so once again we were leaving the mountains for the coastal desert. We travelled in the Kahn river valley and had to climb up the Stingbank to descend to the plain. Here we had another chance to leave the train to roam the sand and rock with low rises of granite and a fascinating array of rocks to collect. We came across tracks that looked like snake tracks except they would suddenly end; eventually we found the cause - - it was ants, thousands of them scurrying back and forth carrying eggs and twigs. They seemed to be relocating their nest. The track was about 20 yards long and worn about ½ inch deep! Once again the desert was endless flat sand with a few plants; we saw oryx, ostrich and springbok; they must be very hardy. We left the train at Arandis, close to the uranium mine, and boarded the buses to visit Gounikontes, which is an oasis actually in the bed of the Swakop river. As we crossed the desert we passed through several long black ridges standing above the plain, some were 1m across, up to 10m for others. These are a dolerite dyke swarm that intruded the area 130ma with the break-up of Gondwana. We descended through steeply dipping granites and mica schist strata into the river gorge where there is an olive grove and many trees. Earlier last century there was a thriving vegetable business using the seasonal water but the whole enterprise was destroyed in 1934 by a catastrophic flood which they could hear coming 3 hours before it arrived; this did not save the livestock or some of the people! I wonder when the next one will be! We then drove up the canyon and out on to the plain where we stopped to look at the amazing Badland scenery carved by the Swakop river. It was a real ‘moon landscape’ with dozens of river beds where water must have poured over the edge over the millennia, but it was hard to see where it had come from; it must have been from the far away Journal of the Bath Geological Society, No. 25, 2006 27 mountains. The granite in Namibia’s arid conditions is a soft rock as the frequent heat variation and the salt-laden fog causes it to disintegrate into granules that then get washed or blown away. caused by a superheated steam eruption; red finger dunes reaching out from the Kalihari; visiting the Giants’ Playground, balanced dolerite blocks, and the Quiver tree forest, photograph 4, in time for sunset. We drove along Welwitchia drive to see these strange plants, photograph 3, which only ever have two leaves which get longer and longer and split lengthways. Some of the plants are immensely old and are obviously well adapted to desert conditions. Photograph 4: Quiver Tree Forest at sunset Photograph 3: Plants along Welwitchia Drive We drove down the coast between the dunes and the sea to Walvis Bay where we visited, briefly, the salt works and saw the flamingos in the lagoon. One of the features of Swakopmund is the salt, sand and gypsum roads. We walked on the beach and collected pebbles for polishing, then watched the sun go down over the sea. This is the only day we experienced the fog, which is amazing as it usually a feature of the morning four days out of five. A word about water in the desert - for many years all water was shipped into coastal towns until it was realised that all the water that flowed from the mountains and Escarpment to disappear before reaching the sea must be going somewhere! Nowadays large underground aquifers provide enough water for everybody. In Swakopmund there is a fascinating museum-cumjewellers called the Kristall Galerie. It has large rock specimens outside including stromatolites, tourmaline in situ, boulders with amethyst and many more semi-precious stone-bearing rocks. Inside there is a collection of huge quartz crystal clusters, the biggest is taller than a person, weighs 14100kgs, is 520 million years old and was found on a farm in a cavern along with several smaller clusters. The gallery has displays of crystal clusters of tourmaline amethyst, dioptase, sulphur, pietersite and much more. We finally started the return journey, back to Windhoek and across the plateau to Keetmanshoop passing dry river beds; the escarpment running parallel for miles then gradually receding; past Brukkaros, a carbonate volcano 28 That night we left Namibia but it was not the end of the trip. In South Africa we stopped at Upington and travelled through the vineyards around the Orange river to visit the Augrabies Falls, then, on our last day we popped in for a quick visit to the Big Pit at Kimberley. All in all a memorable trip leaving me wanting to go back; there is so much more to see, - Spitzkoppe and Brandberg, the Fingerklip, Sossusvlei and Waterberg to name just a few. YET MORE LIMERICKS Asthenosphere The asthenosphere really is not An inviting or welcoming spot, For its frightfully deep (Nuff to make the skin creep) And the climates oppressively hot. S. A. Mc Burnie Aquifers The aquifers under our home Beneath filtering trees, grass and loam, Amid layers of clay Are a tri-tiered array Of groundwater, cached in a dome. Carol June Hooker Amygdale Im sure it wont come as a shock That small bubbles appear in a flock Filled with stuff of all sorts, Such as calcite and quartz; Theyre amygdales in igneous rock. Sheila B Journal of the Bath Geological Society, No. 25, 2006