Hard braking on the steep winding descent. Sun reflecting off the distant Indian Ocean, to be replaced by glints off the Umgeni River. Houses scattered in happy abandon across the escarpment, with the local residents up and about in the dawn. There is an election tomorrow, so it is a long weekend, and there are hints to remind us all that a big party had gone down the night before. But this is a new day, with the dawn fresh and clear to blow away the cobwebs.
A civilised river crossing
to be turned away
It is Halloween – which is perhaps a good day to be looking into the dark past. The day hadn’t started out well – Alex, our trusty cameraman, and I had arrived at the Krantzkloof Nature Reserve only to be turned away as there was a trail run on that morning. The whole idea had been to riff on gorges and rock joints. But now we had to go to Plan B. Which wasn’t a chore, but a bit frustrating to say the least, as we had hit the road at 5 am. This had meant getting up at 4 am, which is pretty early.
Happy cows wandering across Ordovician Silurian aged Natal Group Sandstone with the deeply incised Valley of 1000 Hills below
Lugubrious cows chewing the cud
The winding road down into the valley was some compensation, and there certainly was plenty to look at from a geological point of view – 1.1 billion year old granites and granite gneisses, towering cliffs of Natal Group Sandstone, and some wonderful emergent inselbergs sparkling in the morning sun. Not to mention the feisty goats sunning themselves on the blacktop or the lugubrious cows chewing the cud – the conservative ones on the verges and the more adventurous ones parking themselves right in the roadway.
Pass of the Angels
A climb over the Pass of the Angels
After hacking through a few river crossings, some ventures up some dead-ends just to see what was there, and a climb up over the Kwa Ngcolozi Pass (Pass of the Angels), we found ourselves at our Plan B destination – a normal fault below the high plateau of Natal Group Sandstone.
some contradictions in the term ‘normal fault'
Which brings us to where we need to be – a riff on things geological and geomorphological. This fault is what is called ‘normal’ which is perhaps pertinent in today’s trend towards newspeak and gobbledygook and such terms as the ‘new normal.’ Having lived with this terminology for so long I barely give it a second thought, but there does appear to be some contradictions in the term ‘normal fault,’ but let us not digress.
Where we were. The geological map of a heavily faulted area. Greenish grey is Tillite, light blue is Sandstone, and pink is Granite. Bold black lines are faults.
On the downslope side of the fault is 1.1-billion-year-old granite and granite gneiss – the weathered remnants of what used to be the core of an ancient mountain range. On the upslope side of the fault is Dwyka Tillite – a glacial deposit which was laid down in the Late Permian when Gondwana was situated over the south pole, and in the grip of vast ice sheets much like what exists in present day Antarctica.
The mashed up, tectonised, chewed up material
The layer cake geological sequence is, from oldest to youngest; Granite, Natal Group Sandstone and Dwyka Tillite. Only the tillite and granite are represented in the fault. Between the two rock types is a fault breccia (pronounced ‘brechia’) which is the mashed up, tectonised, chewed up material which formed when these massive movements in the Earth’s crust took place.
The icing sits against the chocolate layer
So the layers in the cake have been disrupted. Imagine a cake with chocolate at the bottom – representing the granite, vanilla in the middle – representing the sandstone, and icing on the top - representing the tillite. Run a knife through it, and then drop the right hand side down so that the icing sits against the chocolate layer. You have just reproduced a model of faulting that illustrates the point – tillite against granite. You will also observe that the sandstone is still present on the right side of the fault, but that it now lies at a much greater depth.
So this is how the stratigraphy gets disrupted, which has all sorts of implications from a geological and geomorphological point of view. Those implications we shall leave for another day.
a David Attenborough impersonation
The sun beat down on us as we wandered up and down across the fault zone. There is some great footage by Alex as I hack into granite, breccia and tillite alike. There are cars going up and down the road drowning out my attempts at a David Attenborough impersonation. There are a couple of dodgy scrambles up the rock face to get a closer look at things.
But all in all, we had fun. However the real fun was editing out the bloopers, the roar of the passing cars, the cheers of happy people on a sunny day on a weekend before an election, and the impending goblins, gremlins and angels buried deep in the editing software. It was a happy Halloween indeed.
Go check the video out here.
Find out about these courses we are building out to support you in the classroom below.
Evolution of Landscapes
We take an in depth and integrated look at how our Earth formed, the development of plate tectonics, how this operating system drives the rock cycle to form the rock trinity of igneous, metamorphic and sedimentary rocks. We also dive into the formation of fold mountains, folding, faulting and igneous intrusions. And armed with this knowledge we then venture out onto the peneplains and pediplains to do battle with scarp retreat and the evolution of landscapes.
We are building out courses on geomorphology to support you in your teaching endeavours, and are pushing to launch these in early 2022. So why not leave us your best email address so that we can keep you updated on when we launch – it will be a grand day for us all, so we look forward to having you on board and engaging with you on what would be of particular use to you in the classroom – valuable feedback for us when trying to decide on where to put our energies.
So looking forward to adventuring with you