1. Fish River Canyon

                                 
                                         Millions of years ago in Namaland.
                                A trip to Namibia taken by our treasurer.

    By Maire Lohan, 2012

As a member of the Galway Geological Association I’ve enjoyed taking part in the activities of its first year of existence – completing the course in Geology in the Moycullen VEC, going on wonderful field-trips in the Burren and Connemara and attending some fascinating lectures at NUIGalway. In November I ventured further afield and travelled to Namibia on holiday with my husband, David, who took the photos below. Not knowing much about the country, I did some research before we left and realised that there were so many places with wonderful geology that it would be difficult to plan an itinerary for our limited time. When I visited a region there called Namaland I realised that the word has other meanings than the gloom-laden one it has in this country……….

Millions of years ago Namaland was a very different place and over that time­­ it has become imprinted by some amazing geological events. Namibia is an enormous country – 825,418 km2 compared with Ireland’s 84,412 km2 – with a population of just 2.3 million, so there are vast, open areas of desert, thorn-scrub, savannah and salt pans. The Namib desert stretches along the entire coastline and is backed by the Great Escarpment beyond which is the Central Plateau. The Kalahari desert lies to the east. The only perennial river in Namaland is the Orange River which forms its southern boundary with the Republic of South Africa.

Fish River Canyon
(see photos below)

Situated in complete wilderness and second only in size to the Grand Canyon, this gigantic gorge is 160 km long, up to 27 km wide and in places almost 550 m deep. Some 770 million years ago the original layers of sediments and volcanic rocks were invaded by doleritic magma which formed prominent dark dykes that can be seen on the canyon walls. By c. 350 million years ago erosion had removed most of the Nama rocks and the initial river valley had formed as a wide meandering depression, which was eventually filled up with glacial sediments, sandstone and shale. The canyon as we see it today began to form during uplift after the break-up of Gondwanaland c. 130 million years ago.  The increased velocity of the river caused it to incise deeply, revealing the deepest layers as outcrops on the canyon floor. Along the fault zones forming the sides of the canyon groundwater rises to the surface to create a number of sulphate-and fluoride-rich hot springs believed to have natural curative properties. The Fish River is an exception among Namibian rivers in that it retains perennial pools outside the rainy season.

Though not as jaw-dropping in perpendicular scale as the most-photographed sections of the Grand Canyon, the sense of isolation and absolute wilderness here is unsurpassable. The hotel where we stayed is the only one permitted on its entire rim and is some 2 hours journey from the nearest road. A hair-raising trip right into and along the floors of canyons within canyons will not be quickly forgotten.

Petrified Forest near Twyfelfontein

The Petrified Forest (fig. 2) lies further north in Namibia (Damaraland) in a dry, rugged area. Scattered all over the site are many fossilised trunks of tall trees, lying vertically, which are estimated to be c. 280 million years old. Members of the early Cordaites family of trees, they grew to heights of over 40 m. and are ancient ancestors of present-day conifers and ferns. About 320-270 million years ago Namibia was covered in ice fields and glaciers during the Great Gondwana Ice Age. As the waters melted, floods ripped through this ancient forest, tree trunks were literally snapped off and carried far distances. At this site they were buried almost immediately under a thick layer of sand and rubble. Further sedimentation over many millions of years resulted in the trees being buried under hundreds of metres of overburden. Immense pressures caused quartz in the sediments to dissolve and the silica-rich solution permeated the wood and replaced it with crystalline quartz. When the ancient continent of Gondwana split apart surface levels rose. In the following millions of years ice ages came and went and erosion, first by water wash and later by desert wind, eventually uncovered the tree trunks.

Wandering around this site and following the haphazardly-scattered tree trunks until they became covered by the ground made us really appreciate the power of water and wonder where these trees might have originated. Unfortunately, our guide could only say ‘from a far distance’.

Dinosaur Footprints at Otjihaenamaparero

In the Otjiwarongo district of northern Namibia, we travelled to a privately-owned farm where crossing tracks of dinosaur footprints can be seen on flat sandstone outcrops of the 190 million year old Etjo Formation – think a flat Burren landscape except with very hot red sandstone. These sands accumulated under increasingly arid conditions as wind-blown dunes - similar to dunes further south in the Namib desert today. Imprints in wet sediments around waterholes - fed by occasional rainfalls and thunderstorms - were covered by other layers of wind-blown sand. They were preserved as trace fossils when the sand solidified into rock due to immense pressure. All tracks show the form of the 3-toed, clawed hind foot of a bipedal animal. The longest track (which can be followed for about 28m) contains 30 imprints (c.45 by 35cm) spaced some 70-90 cm apart which are believed to be made by Ceratosaurus. (fig. 3)

Some tracks contain smaller imprints c.7cm long spaced about 28-33cm apart; these are believed to be those of Syntarsus (fig. 4) . Due to the unfavourable changes in climate, it is assumed that the animals became extinct not long after they left their footprints. However, as no body fossils of these creatures have been found in the area, the identification is based on comparison with other sites.

Tracing the tracks of these animals of such different sizes that were forced to concentrate near shallow waterholes brought into sharp focus the fragility of life in times of climate change.

Petrified dunes near Sesriem

The Petrified dunes (fig 5) are situated near Sesriem, on the eastern edge of the Namib desert which is the oldest desert in the world; they are sometimes called the Fossil dunes because they contain fossils of the ancestor of the modern-day ostrich. They provide wonderful visual evidence of an earlier desert. Towering red sandstone cliffs, some reaching 90 m, are remnants of a dune system that was created during a period of accumulation of wind-blown sand c.65 million years ago. As the climate changed, gradually getting wetter, the additional moisture caused the sand to solidify into sandstone which is estimated to be 23 million years old. The establishment of the cold Benguella Sea current along the west coast of Africa, some 5 million years ago, heralded a return to very dry conditions and the development of the current dune system.

The Meteorite at Hoba

In the north of Namibia near Grootfontein, the Hoba meteorite is the largest known single meteorite in the world.  (fig 6) Tabloid-shaped, it measures 2.95m by 2.84m and its thickness varies between 122cm and 75cm; when found in 1920 it was estimated to weigh 66 tons but erosion, scientific sampling and vandalism have reduced its bulk to a present estimate of 60 tons. It comprises 82.4% iron, 16.4% nickel, 0.76% cobalt and other trace elements. It is classified as an ataxite, a structure-less, relatively rare and very dense iron meteorite. The presence of a rare radioactive nickel isotope has enabled scientists to date its fall to earth at less than 80 000 years. Analyses of the age of the meteorite vary between 190 and 410 million years.

It is situated on the edge of the Kalahari plain which is underlain by white calcrete, under which are ancient granites, dolomites and limestones. No crater or altered rocks have been found associated with the impact site; the flatness of the meteorite on both major surfaces possibly slowed its terminal velocity sufficiently to allow it to skip across the lower atmosphere in the way a flat stone skims across water. After the meteorite fell it was gradually covered with a layer of calcrete formed by the evaporation of near-surface groundwater – suggesting a more humid climate in the recent geological past. Ease of access to this huge meteorite encourages one to touch it and examine it closely. The imagination can go into overload when one sees it hurtling through space and landing at Hoba without leaving any perceptible crater.

Tourist literature rightly proclaims Namibia to be ‘a geologist’s paradise’. Having visited these sites it is very easy to see why. I certainly wish I could have stayed longer to explore further – and that my geological knowledge was much, much deeper.

 

References

Dinosaur Footprints: info from a leaflet printed by the owner in which he refers to www.dinosaurtracks.com      

Fish River Canyon: www.fishriverlodge-namibia.com/ ; www.gond-collection.com?id=57

Hoba Meteorite: Info from leaflet at site. Further info at www.giantcrystals.strahlen.org/africa/hoba.htm       

Petrified Dunes: Info from leaflet at Namib Desert Lodge Hotel. 
www.namibian.org/travel/lodging/private/namib_desert_lodge.html

Petrified Forest: www.namibia-1on1.com/petrified-forest.html

Hover your curser over a photo to see captions.