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.
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Logging Tasks:
1. At these coordinates S28 27.874 E020 17.108 (in the corner) there is a formation caused from the water flowing over the rocks. Describe how this differs from the surrounding rocks and what causes it? Can you name this type of formation? (Hint: answer is in the listing.)
2. At these coordinates S28 27.858 E020 17.210 you will find a split rock. Describe this rock in terms of colour, grain and what rock would you say this is?
3. At the coordinates S28 27.824 E020 17.217 there is an Oxwagon etched on the rock. What name appears below it?
4. OPTIONAL: Please share your experience with the caching community by uploading photos of the landscape, any geological features at the site you found interesting and/or your caching party with your log. No spoilers please.
Overview
Riemvasmaak is 74 563 ha in extent. It is situated in the Northern Cape Province and borders on the Orange River in the south and Namibia in the west. Commercial farmland occurs to the north and northeast of Riemvasmaak while the National Parks Board owns adjoining land in the east and leases 4 270 ha of Riemvasmaak land from the Riemvasmaak Trust in the southeast.
Many people ask what is to be found at Riemvasmaak. Picture a granite canyon with rock faces 80 m high, the home of many exotic raptors nests, opening up to the kind of blue sky that can only be found over the Kalahari. And dispersed in and around the rocks, glorious hot springs. Chalets and campsites with rudimentary ablution facilities can be found here.
Riemvasmaak’s hot springs are reputed to be good for skin ailments and rheumatism. You’d think that with the ambient temperature touching 36° C, a hot bath would be the last thing on anyone’s mind. But not at Riemvasmaak. Set in a kloof and surrounded by impressive rock cliffs the spring has a soothing effect on body and mind.
Geology & Soils
The geology of the region is tightly coupled to the landforms of the region and is comprised of 3 main geological groups: the Namaqualand Mobile Belt sediments and intrusive rocks; the Nama sediments comprising the plateau; the more recent Kalahari and Quaternary sands.
Numerous pegmatites exist in the region and form the basis for the mining industry that existed in the region in the past. Pegmatites are highly crystallized veins in granite.
The Riemvasmaak settlement is situated on an alluvium with supporting Gneiss with an inserted mission. The Gneiss at Riemvasmaak under the alluvium is however eroded to a depth of 70 m.
The dominant soil type in the area is alluvial sand and sand dunes. Metasediments of the Korannaland formation can be traced from the east and south into the area but further north and east appears other metasediments of which some are known in the Korannaland formation. These rocks are grouped in the Koelmanskop metamorphic suite. No stratigraphic sequence can be recognised in them because the metasediments are usually found in the granites as big enclosures. Granites that are in contact with each other ages are not known.
The oldest group of rocks is represented by the basement material of the Namaqualand Mobile Belt which dates to about 1.1 billion years. These are sedimentary, volcanic and intrusive rocks. Following the collision of the original continental material or Kaapvaal craton with other major blocks to the north of it (e.g. the Zimbabwe craton) an unstable region called a mobile belt or geosyncline was created. The sedimentary and volcanic rocks of the Koronnaland sequence and Hartbees River complex were deposited within this region at the time and the intrusive rocks of the Keimoes and Eendhoorn suites are also related to this collisional event. Subsequent erosion over millions of years has exposed both the basement gneisses and other material of the Namaqualand Mobile Belt. This material forms much of the rocky pediments at the base of mountains in the region. An unrelated and substantially more recent event (from 550 million years ago) has been the laying down, within a shallow sea environment of the Nama Group of sediments. It is this sedimentary grey and red-brown quartzite, shale and conglomerate which comprises the plateau and steep rocky slopes of Riemvasmaak. The Kalahari group of sandy alluvial depositions occurred relatively recently during the Quaternary (the most recent 2.6 million years of Earth's history). It is these wind- and water-transported materials which comprise the sandy pediments and sandy dry river beds below the plateau today.
There is another aspect that is visible here, but is in its infancy - a tufa waterfall. It is formed when water running over dolomite rock absorbs calcium. Mosses which grow on the rocks in the stream extract carbon dioxide during photosynthesis which precipitates the calcium from the water to deposit it as layers of tufa on the surface of the waterfall – a process that takes millions of years.
Climate and Rainfall
The area is semi-desert, with low summer rainfall levels. The average summer temperatures differ between 18° C and 36° C, with extremes of up to 43° C. Winter temperatures are moderate and differ between 30° C and 20° C and minimum temperatures dropping as low as 0ºC.
The area falls within a rain shadow. Rain generally occurs early in spring and then again between February and April. Average rainfall of the area ranges between 75 and 125mm per annum.
Topography
The topography of the area around Riemvasmaak is characterized by the Kalahari desert, wavy hills, sand plains and red sand dunes.
The topography of the area where the settlements are located is generally flat with an estimated slope gradient of 1:10. However, both settlements are surrounded by mountains which pose a threat to the settlement due to small tributaries flowing from these hills/mountains down to the settlements. As a result of these tributaries and streams, a huge water catchment area is formed where they meet (in particular the Mission area). This is the area of concern due to the flooding history associated with it.
The Molopo River catchment area is the largest of the four main catchment areas which decrease in size from the Bak, Kourop and Orange River catchments respectively. Only three of the twenty water points (boreholes, dug wells, fountains , natural springs as well as the Riemvasmaak Hot Springs) sampled by Toens (1994) contained potable water. The remaining sources had excessive levels of either fluoride or nitrates or were too saline for healthy human consumption.
A brief history
Riemvasmaak is known as one of the first land restitution projects of the new democratic government of South Africa, and was registered as a Presidential Launch Project; as a result, this area has had a very high political profile.
Between 1973 and 1974 the residents were forcibly moved to Namibia and the Eastern Cape. It was during this time that the apartheid government utilized this area as a training ground for the South African Defence Force. Twenty-one years later in February of 1993, the entire 74 000 hectares of land was given back to the rightful people. The Xhosa people were relocated at the Vredesvallei settlement on the banks of Orange River. The Nama people, who account for approximately two-thirds of the Riemvasmaak community, were settled around the Old Mission Station.
By the end of 1995, most of the original residents were restored to their land, and by 2002 the people of Riemvasmaak were handed the deeds to the plots on which they lived.
What’s in a name? There’s another story about the origin of Riemvasmaak’s name. According to it, two Bushmen who’d shot cattle belonging to a farmer were caught and taken to the village at sunset.
A ‘riem‘ (belt/strap) was used to tie to an oxwagon for the night, but the next morning they were gone. The 'riem' was obviously not ‘vas’ (tight) enough, and from that the community got its name.
References:
On site information.
Riemvasmaak – Northern Cape - Parliamentary Monitoring ...
Monitoring in Riemvasmaak - Plant Conservation Un