An Earth cache is a special type of Virtual Cache that is meant to be educational. Therefore to log a find you must demonstrate that you have learnt something from the site and experience.
Send your answers to us in an email via our profile page.
Any logs not accompanied by an email will be deleted.
Logging Tasks:
YOU WILL NEED A LITTLE WATER FOR THE EXPERIMENT.
1) Explain what makes this river an ephemeral river.
2) Describe the texture and colour of the sand at the listed coordinates.
3) Take a small sample of the sand and moisten it. See if a ball can be formed. What is the result and explain the reason for this.
4) Visitation confirmation - On the south side of the pole is a plaque. What is the inscription on this plaque?
5) Optional: Share your experience with the caching community by log or by uploading photos of special sightings you’ve had while visiting the park.
Today Unions End still marks the meeting place of borders of South Africa, Botswana and Namibia. This is also the point where the dry Nossob (meaning dark clay) River enters South Africa from Namibia. Here you may alight from your vehicle and examine the sand of the surrounding area.
THE KALAHARI DESERT
The Kalahari is a semi-arid region with the largest continuous area of sand in the world. The modern Kalahari Desert, a small remnant of the original dune desert, lies within the Kalahari sand beds – a massive expanse of sand that covers 1 630 000 sq km from just north of the equator to the banks of the Orange River in South Africa. The sand originated from rocks lying in a shallow basin that were eroded by wind over millions of years.
The red colour of the dunes is caused by iron oxide, which covers each sand grain. The rainfall of the area is too low to reduce this iron oxide, and a wonderful variety of colours can be found in the desert sand. The dunes of the Kalahari hide the ancient sedimentary rocks which are believed to be rich in fossil deposits. The dunes are fixed and are no longer moved by the wind. They do, however, owe their characteristic shape to wind which exposes the moist sand beneath. The moist sand is then eroded further. The sand that is removed is deposited on the southwest side of the dune, which results in a more gentle gradient. These longitudinal dunes are called seif dunes, an Arab word meaning ‘sword’.
Five groups of Kalahari Sands are recognized and range in colour from red in the dunes, through to yellow-brown, white and grey on the pans and riverbeds. The sands are predominantly of aeolian origin, emanating from within the basin itself. In the southwest, the sands are piled into vegetated linear or seif-dunes. They break down into a more gentle undulating terrain about 40 km east of the Nossob River.
Soils in the Kalahari are largely based on sand, are reddish in color, and are low in organic material. Chemically, they are relatively alkaline, and they are extremely dry. In and near the pans, the soils tend to be highly calcareous or saline, and frequently they are toxic to most vegetation.
Soil textures are classified by the fractions of each soil separate (sand, silt, and clay) present in a soil. Classifications are typically named for the primary constituent particle size or a combination of the most abundant particles sizes, e.g. "sandy clay" or "silty clay." A fourth term, loam, is used to describe a roughly equal concentration of sand, silt, and clay, and lends to the naming of even more classifications, e.g. "clay loam" or "silt loam."
THE GEOLOGY OF THE KGALAKGADI NATIONAL PARK
The floor rocks of the Kalahari Group are only known from boreholes. It consists of rocks of the Karoo Sequence with its associated intrusions of dolerite. The pre-Kalahari topography was dissected by rivers which drained in the direction of the present Botswana. The distribution of the oldest formation of the Kalahari Group, the Wessels Formation (clayey gravel), and the overlying Budin Formation (clay) was also determined from borehole records. The Karoo Sequence was probably the source of these rocks. The overlying Eden Formation (sandstone, grit and conglomerate) had a source which could yield much sand. All these formations were deposited under fluviatile conditions. The Mokalanen Formation (calcrete) and the Gordonia Formation (sand) indicate a change from a humid to an arid environment. The Lonely Formation (clayey diatomaceous limestone) was deposited in a lacustrine environment. It also indicates a higher rainfall in an otherwise arid period. The Goeboe Goeboe Formation consists of clay and sand in the pans and rivers.
The pans and the river floors are practically horizontal with sparse or no outcrop and are covered by brown to white, fine grained sandy sediment. Some pans have a white salt crust and during dry periods mud cracks and peels appear on the surface. Analysis on the mineral composition indicates that quartz, calcite, montmorillonite and feldspare are the main components.
THE NOSSOB RIVER OF THE KALAHARI
With an annual rainfall between 200 and 350 mm annually, water is scarce in the Park. Due to the sand, water leaches quickly through the sand forming large underground lakes. This groundwater is then pumped from the Nossob River to provide water to man and animals inside the Park. The average depth of boreholes in the Nossob River is 75 m.
The Nossob is an ephemeral river, meaning that it only flows for a short period during a very good rainy season and perhaps twice every 100 years. The Nossob River last flooded in 1963/64 (reference SanParks). It does, however, carry rainwater in the wet season and there is moisture beneath its beds, a precious resource that is tapped to sustain life in the area. The Nossob meanders a lot. In the north the riverbed is wide with slightly raised alluvial plains and widely flanking dunes. Further downstream between the Nossob and Twee Rivieren restcamps, the number of trees seem to dwindle and the course suddenly cuts through calcrete deposits turning south-westward. The banks are relatively steep, narrow and rocky.
References:
SanParks booklet Reception Nossob Camp
http://www.sanparks.co.za/parks/kgalagadi/tourism/history.php
The geology of the Kalahari Gemsbok National Park - S. J Malherbe