Triple Watershed! EarthCache
Hidden : 2/5/2013
Difficulty:
1.5 out of 5
Terrain:
1.5 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

A triple watershed!

 

The Witwatersrand is a large sedimentary range of rocky hills in South Africa. The Witwatersrand runs in an east-west direction through Gauteng. The word in Afrikaans means "the ridge of white waters”. It is a well known fact that this quartzite ridge, the “Witwatersrand”, that stretches east to west from Bedfordview to Krugersdorp respectively, forms a main continental watershed dividing rainfall to flow to the Limpopo in the north and the Vaal River in the south.  The most important reason for this ridge to exist is that the quartzite forming it is by far one of the hardest rocks found and takes millions of years to weather away, especially by water. To get an idea of the hardness of quartz, if one would research the Mohs scale of hardness used for minerals, quartz is number (7) on this scale. The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science. The Mohs scale is a purely ordinal scale. For example, corundum (9) is twice as hard as topaz (8), but diamond (10) is four times as hard as corundum.
 
What is not such a well known fact is that the location of this earth cache is approximately where there is a triple watershed. It might not be dividing the water to two different oceans, but it divides the runoff on the western part of the ridge stretching from Aasvoëlkop to Krugersdorp to run in an easterly and westerly direction until it meets again some distance north of the Lanseria airport (at S25° 52,567’ E27° 55,640’) before it flows into the Hartbeespoortdam. A major drainage system for half of the area between Johannesburg and Pretoria! A possible reason for this east west division of water is the formation of the granite dome that looks almost like a helmet when viewed on a plan. This dome covers a large part of the area between the ridge and Pretoria with its centre approximately at Four Ways. During the uplift of the granite millions


Fig. 1 - Halfway house granite dome


of years ago the highest point of the dome would probably have been in the middle of the yellow area in figure 1 meaning a downward slope to the east and the west that could have resulted in a watershed running north to south that ended more or less at the location of this earth cache.

The triple watershed is shown in figure 2. WP (A) is the highest point in the area. The line H-F-A-D-E is the approximate position of the Limpopo – Vaal watershed. The line A-B-C is the east west watershed this earth cache refers to.


Fig. 2 - The triple watershed

In order to qualify to log this cache, you need to answer the following questions and e-mail the cache owner. Any logs not accompanied by an email will be deleted.

1) Take a photo of you and your GPS at location (D) (the coordinates of this earth cache) with the water tower visible and include in your log [Optional]. This is an extremely busy road, use extreme care. It is recommended to park around the corner in Beverley Drive South.
2) Visit WP (B) where there is fresh broken rock and describe what it looks like, colour and structure? Using a magnifying glass of 8X magnification or more will be of great help to reveal the structure of the quartzite very clearly.
3) If you are standing at WP(D), which wind direction will the runoff flow?
4) Name the streams (or rivers) that the water will flow in (east) to get to the Hartbeespoortdam starting just east of the water tower?
5) Name the streams (or rivers) that the water will flow in (west) to get to the Hartbeespoortdam starting at WP(F)?
6) On Mohs scale of hardness, which two minerals come before quartz (number 5 and 6)?

Additional Hints (Decrypt)

Erzrzore gb fraq gur nafjref!

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


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