Geology
There are two contrary hypotheses how the rocks on site were piled up:
I) In primeval times the family of the giant Mbombo used to live further north (today Democratic Republic of the Congo) in the area of the Kuba Kingdom and the three giant kids named Nyonye Ngana, Chonganda, and Chedi Bumba stacked up the boulders. This theory could explain today's name of the place Giants Playground, but there are no references in Kuba history to have had an impact on rock formations in Namibia.
II) A second theory is favoured by most geologists. They start from the premise that in the time of the Early Jurassic epoch (that's 180 Million years ago when heavy tectonic plate movements devided the supercontinent Pangaea into Laurasia and Gondwana) magma pushed its way through long cracks into the overlaying Karoo rocks. When the magma cooled off (in this case the solidified magma is called dolerite) it also began to shrink. That caused first vertical and horizontal rifts. Over tens of millions of years the softer Karoo rocks were eroded and unfold the dolerite on the surface so that rain and ground water could start to pit the existing fractures. The latter process is called spheroidal weathering and is the reason for the spectacular dolerite outcrop, that you can see here today.
This cache description was intentionally kept brief to just provide a rough overview of the geology of the spot. Nevertheless the information should be sufficient to both understand what happened here in the last 180 Million years and to cope with the questions associated with the EC. For advanced details please click the links to wikipedia articles in the text or continue reading with the literature listed at the bottom.
Global view beyond Giants Playground
More formations caused by spheroidal weatheringloss can be found world-wide. The EXTERNSTEINE rocks in the German Teutoburg Forest are a good example in sandstone. Others in granit are Karlu Karlu … in the Australian Northern Territory, Myanmar's Golden Rock or the Haytor in South England's Dartmoor (Geological Dartmoor.).
Log Requirements
Please have a look at the four tasks below and send us the answers via one of our GC profiles (J or ts). After submission you are allowed to log online immediately without waiting for further approval. In case of any discrepancies we will contact you. Please make sure you've sent your e-mail address along with your message so that we can contact you directly.
- Task 1: Which of the two geneses mentioned in the first paragraph seems to be more likely to you? Explain why in your own words.
- Task 2: To get an idea of the time scale of weathering processes, take two small dolerite stones and rub them against each other. Tell us about your experience with respect to hardness and give us based on your abrasion experiment an estimation on the amount of material that spheroidal weathering eliminates every year (this question is more about your valuation than an exact number).
- Task 3: On some of the rocks you will find white stripes. Explain where this comes from (hint: it's more a biological than a geological phenomenon. You might be lucky and catch out one of the polluters).
- Task 4: Take a picture on site and post it along with your online log. The picture has to either show your GPS device or your GC nick name written on a piece of paper or on your hand in front of the rocks. In accordance with the updated EC guidelines this is an obligation effective 10th June 2019. Logs without the requested photo proof will be deleted after 24 hours.
How to get there
The Giants Playground belongs to the Farm Gariganus and you have to pay a entrance fee (55N$/person) at the farm office (see waypoint FO) to enter the geological site. The ticket will additionally give you access to the nearby Quiver Tree Forest where you might want to have a look at the Quiver Tree Cache.
From the office the Giants Playground is a few kilometers down the gravel road (C17) to the East. There is a fenced parking area where you can start your 45 min sign-posted walk through the rock formations. Since the route of the path is ambiguous from time to time and the signs are not consistent, it is recommended to take your GPS with you in order not to get lost in the lithic maze. Please also do not forget water and sun protection.
References