Photographer's Note

Namibia is like an open book for anyone interested in geology, rocks are exposed and the effects of erosion is plain to see. Sesriem Canyon is virtually hidden until one walks to its rim. A slot canyon well worth walking through to read a visual history of the area's climatic past.

This shot was taken on our recent trip around the country.

Sesriem Canyon owes its name to the first settlers who had to connect six lenths of leather rope (Afrikaans: ses rieme) to scoop water out of the canyon. Its geological past began in the middle Tertiary about 30 million years ago. At these times a true desert climate prevailed as in the present Namib Desert. Large parts of the country were covered by up to 200 m thick desert sands, which later solidified into the Tsondab Sandstone Formation. As so often in the history of the earth a climatic change occurred and wetter (semi-arid) conditions commenced. Numerous rivers were formed which rose in the area of the Great Escarpment further to the east and unlike today often even reached the Atlantic. The Tsauchab River was one of these. This river transported large amounts of erosion debris and dissolved carbonites form the nearby Naukluft and Zaris Mountains and deposited these gravels on the desert sands of the Tsondab Sandstone Formation. This debris is about 50 m thick and fans the foot of the Great Escarpment. The carbonate transported in the river water was precipitated and this lead to a cementation of the deposited sand and boulders forming conglomerates.
The actual formation of the Sesriem Canyon was initiated by a drop in sea level about 2 million years ago. This drop was connected to the commencement of ice ages in the Northern Hemisphere. Large amounts of seawater were absorbed as ice in the newly formed glaciers, which caused a worldwide drop of the sea-level. This led to an increase of the gradient to the ocean and thus to an increase of the erosional forces of the rivers, which resulted in the Tsauchab cutting into its own, previously deposited conglomeratic sediments. The erosion processes, which formed the small canyon (about 30 m deep and 3 km long) still show this effect, when the water flows at high speed through the gorge in good rainy seasons. The recent return to full arid conditions makes further shaping of the canyon take place progressively slower.
During a walk through the Sesriem Canyon you can read its geological history from the steep canyon walls. A distinct change from the fine sandy layers to mighty boulder beds is obvious. This sequence in the sediments reflects the different water load capacity of the Tsauchab River during the single sedimentation phases. Coarse boulders point to strong flowing water with large transportation power and thus high rainfall. Fine grained sand deposits are an indication of weaker flowing water due to lower rainfall. By means of such outcrops, the geologist can reconstruct the climatic history of the whole region.
After good rainy seasons, water remains in the gorge for many months. Numerous tree branches have trapped alluvial material, showing very impressively how strong the floods in the canyon can swell. However the Tsauchab, which hundreds of thousands of years ago poured into the Atlantic near Meob Bay, only flows sporadically for a further 65 km into the desert, before it finally oozes away in the Sossusvlei

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Additional Photos by Rosemary Walden (SnapRJW) Gold Star Critiquer/Gold Star Workshop Editor/Gold Note Writer [C: 2806 W: 84 N: 6959] (31631)
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