One of the characteristic features of the Karoo Heartland is the flat-topped Karoo koppies standing out on the traditionaly flat Karoo landscape. Two of the best known Karoo koppies are Koffiebus and Teebus, visible from the R390 between Stynsburg and Hofmeyr. Koffiebus (the coffee pot) being the wider hill and Teebus (teapot) the narrow one. Ground zero is one of my favorite spots to stretch my legs and take in the views of the Karoo Heartland countryside on the road to and from the north. Koffiebus and Teebus can be seen to the northwest from here.
Safe parking is available at Ground Zero
| LOGGING REQUIREMENTS
In order to substantiate your visit and comply with the educational requirement for Earth Caches you have to submit your answers to the following questions to the CO via the message function on their profile.
Please answer the following questions.
1) How long ago did the lava force its way up through the rock layers and how long after that did the uninterrupted period of erosion start?
2) If the hard rock at the top of a Karoo Koppie is formed by dolerite, what group would the rock below it be from?
3) If you face in a southern direction and look to the right of the road, you will see another couple of flat-topped mountains? What type of flat-topped mountain would you say these are and why? (Locational question)
4) Optional task but not essential to logging the EC. Please post a photo of yourself in front of another icon of the Karoo Heartland located at Ground Zero
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Geological history of the Karoo Supergroup
The Karoo Supergroup was formed in vast inland basin starting 320 million years ago, at a time when the part of Gondwana which would eventually become Africa lay over the South Pole. Icebergs that had calved off the glaciers and ice sheets to the north deposited a 1-km-thick layer of mud containing dropstones of varying origins and sizes into this basin. This became the Dwyka Group consisting primarily of tillite, the lowermost layer of the Karoo Supergroup. As Gondwana drifted northwards, the basin turned into an inland sea with extensive swampy deltas along its northern shores. Rivers drained the mountains to the north and deposited the sediment into these deltas and the inland sea. This formed a 3-km-thick layer known as the Ecca Group, which is overlain by the 5.6-km-thick Beaufort Group, laid down on a vast plain with Mississippi-like rivers depositing mud from an immense range of mountains to the south. Ancient reptiles and amphibians prospered in the wet forests, and their remains have made the Karoo famous amongst paleontologists.
After the Beaufort period, Southern Africa (still part of Gondwana) became an arid sand desert with only ephemeral rivers and pans. These sands consolidated to form the Stormberg Group, the remnants of which are found only in the immediate vicinity of Lesotho.
Finally, about 180 million years ago, volcanic activity took place on a titanic scale, which brought an end to a flourishing reptile evolution. These genera represent some of the extinct, mainly predinosaur, animals of the Karoo:
How did Karoo Koppies form?
Flat-topped hills (called Karoo Koppies) are highly characteristic of the southern and southwestern Karoo landscape. These koppies are hills capped by hard, erosion-resistant dolerite sills. This is solidified lava that was forced under high pressure between the horizontal strata of the sedimentary rocks that make up most of the Karoo’s geology. This occurred about 180 million years ago, when huge volumes of lava forced its way, under high pressure, between the horizontal layers of sedimentary rocks belonging to the Ecca and Beaufort groups, to solidify into dolerite sills. The long vertical fissures through which the lava welled up solidified into dikes. From about 150 million years ago the South African surface has been subjected to an almost uninterrupted period of erosion, particularly during the past 20 million years, shaving off many kilometers of sediments. This exposed the dolerite sills, which were more resistant to erosion than the Karoo sediments, forming one of the most characteristic features of the Karoo landscape, namely the flat topped hills, called "Karoo Koppies".
Types of flat-topped hills (or mountains)
A butte is a small flat-topped hill or mountain. Most geographers would say that a butte is taller than it is wide.
A mesa is a medium-size flat-topped hill or mountain usually with steep slopes.
And a plateau is a really large flat-topped hill or mountain that rises sharply above the surrounding area on at least one side.
References:
Wikipedia - Karoo Supergroup
Wikipedia - Karoo
Karoo Space - Layered cake
Firefly the Travel Guy
National Geographic Society
There are traditional caches on both Koffiebus and Teebus, as well as at the Orange-Fish Tunnel outlet nearby. The Landforms #3 Earth Cache is also located at the koppies.