Norscot Koppie (Castle Koppies) Earthcache
When we started out caching, and as we are absolute geological amateurs who love doing earthcaches, we thought that we would’ve liked a few more reasonably simple earthcaches that possibly just look into a few of the tongue twisting names or other basic concepts. Hopefully this earthcache can be one of those.
This delightful small nature reserve, situated in the northern suburbs of Johannesburg is well worth a visit on one of its open days. The reserve consists of 22ha of rocky outcrops, dense bush, open grassland and some small dams that abound with birdlife.
The little blue information board (GZ) belonging to the Geological Society of South Africa, states the following: “the hills in this area form one of a number of Archaean granite tor clusters”, or castle koppies. One of the characteristic features of these rocks or castle koppies are the very large boulders on top of one another. These tors were formed over three thousand million years ago.
(According to Wikipedia “A tor, which is also known by geomorphologists as either a castle koppie or kopje, is a large, free-standing rock outcrop that rises abruptly from the surrounding smooth and gentle slopes of a rounded hill summit or ridge crest.”)
Directly behind the blue information board, you will see some rocks, just protruding above ground. Spend a moment or two studying those, especially the grey one, which is a granodiorite.
The older granites of the Halfway House Dome formed 3 100 million years ago and are among the oldest of the rock outcroppings of the earth’s crust. Various land movements and cycles of erosion have sculpted the present land surface. At present, this surface is in a continuing phase of erosion, which began some 65 million years ago. These granite tors host a variety of trees and shrubs, which have taken a great deal of time to develop. Sadly, the quarries on Norscot Nature Reserve show that man can destroy these fascinating rock formations in just a few years.
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Some random info, about the area, which isn’t geological but is interesting, is that the altitude of the koppies varies from 1440m to 1463m. The annual rainfall is 400-600mm p/a.
Questions:
1) (Location question) In the tree, behind the “registration” table, their is a sturdy upright structure that is most certainly not a part of the tree. Can you identify it?
2) Please describe the rock visible directly behind the Geological Society of South Africa’s blue information board. What colour is it and is it’s texture smooth or rough?
3) How, in your opinion, did the weathering (erosion) of the rocks take place?
4) Just for fun- take a walk down the little path to the birdwatching shelter and even further down to where you can see the castle koppies clearly.
Entrance to the reserve is free however a small donation going towards the upkeep of the reserve is always appreciated. Visitors are required to sign in and out and the friendly ladies and gents at the gate will be happy to answer any questions you may have about your visit. (Remember they are only open the 2nd and last Sunday of every month)
https://en.wikipedia.org/wiki/Tor_(rock_formation)
Acknowledgementy: David Mourant
