The Natural Bridge was formed by the dissolving of the dolomite rock structure through groundwater, and the subsequent lowering of the surrounding land surface.
It belongs to the Malmani dolomite which is part of the Transvaal Supergroup that was deposited in a vast inland sea on the Kaapvaal Craton. It makes up a 2000m thick carbonate sequence over large parts of central South Africa. Dolomite is a fine grained, calcium magnesium carbonate rock, originally formed by the slow accumulation of microscopic grains of calcium carbonate in a warm tropical sea. This process was intimately involved with the production of layers of sticky algal growth, called algal mats, in the very shallow intertidal to subtidal zone. The calcium gets replaced with magnesium, and hence changes from limestone to dolomite. One can notice the fine crinkly lamination that reflects the original sticky algal layers that formed on the sea floor and trapped or precipitated the fine carbonate material.
Dolomite was also instrumental through the algae growth, in generating oxygen from carbon dioxide by the process of photosynthesis on a vast scale, and releasing it into the sea.
References: Geological Journeys – A traveller’s guide to South Africa’s rocks and landforms. Nick Norman and Gavin Whitfield
PLEASE WALK DOWN CAREFULLY TO THE WATERFALL AND THE BRIDGE. THE STAIRS CAN BE SLIPPERY WHEN WET.
In order to log this Earthcache and claim a find, you will need to complete the following tasks / questions.
Educational Logging requirements:
1. At the published co-ordinates describe the rock face in front of you. (Colour, texture and formation)
2. Describe in your own words how this rock has formed. Do you see any evidence of the prehistoric algal mats in the dolomite rocks?
3. Estimate the thickness of the bridge where the Mac Mac River has eroded and formed the natural bridge.
4. In which year was this natural heritage site proclaimed a national monument?
5. Post a picture of yourself/geocaching team, and with your GPSr, with the waterfall in the background (optional but appreciated).
Please do NOT detail your answers in your Found log. Email answers directly to me via the GC.com website.
You may submit your Found log without waiting for confirmation. If there is a problem with your answer(s) I will get back to you. Found logs will be deleted if an email is not received within 2 days.