A team of Umvoto geologists recently set out for four days to conduct field mapping along a major fault network within the Steenbras area. The fault network crosscuts through rocks of the Malmesbury and Table Mountain Groups, with the latter being targeted for groundwater development as part of the City of Cape Town’s New Water Programme. Borehole drilling aims to target secondary fractured aquifers of the Table Mountain Group, namely the upper Nardouw Aquifer and lower Peninsula Aquifer. In fractured aquifers, groundwater is stored in fractures, joints, faults, cavities and along bedding planes. Field mapping was conducted to complement the current understanding of the major Steenbras-Brandvlei Megafault Zone (SBMZ), which has brecciated and broken the lithologies in the area.
After traversing through long, and sometimes treacherous, terrane of near-vertical slopes in the blistering Steenbras sun, a well-deserved break should always be on the cards. Key elements of a good lunch spot should always include a good field partner, a good snack and, most of all, great views.
The SBMZ is a major NE-SW orientated fault system traversing through the Table Mountain Group in the southwestern Cape area, extending from Steenbras in the southwest to Brandvlei (terminating against the Worcester Fault) in the northeast. This fault zone created conduits for groundwater flow in the rocks, which has been the target for groundwater development at Steenbras Wellfield. At the SBMZ Lookout you can see the northern and southern strands of the SBMZ that traverse through the area, while overlooking the Atlantic Ocean at False Bay and the Steenbras Dam. Heads up, always check your surroundings before choosing a spot to rest, because you never know what critters may be lurking about. Staff encountered both a scorpion and a Klipsringer hiding out in the shade of outcrop that had been heavily faulted.
Kogelberg Anticline Lookout
After navigating 4×4 trails for an hour, you will find yourself gazing out over the Kogelberg Mountains. These mountains form part of the Cape Fold Belt, and have been folded into an arch-like shape known as an anticline (or A-shaped) fold. Of any southern African coastal stretch, the Kogelberg Mountains has the steepest and highest drop directly into the ocean. Lunch in this area comes with a display of aerial acrobatics, consisting of swallows swooping and dive bombing for insects at speeds which attempt to break the sound barrier. A new species of butterfly was also recently discovered at this lookout point.
Steenbras Syncline: Crystal Pools
Crystal Pools is situated along the Steenbras River and below the Lower Steenbras Dam wall. The Pools are hosted by the heavily faulted and fractured zone of the Steenbras Syncline. A syncline is the opposite fold of an anticline, in that it forms an inverted arch-like (or U) shape. To the public, this area is well known for its breathtaking hiking trail, in the sense that you require moderate levels of fitness to complete it, but also that it houses exquisite and aesthetically pleasing sights. Two major contributions to these sights would be the majestic waterfalls and pools, which are fed by the Steenbras River and groundwater through fractures related to the fractured Nardouw Aquifer. Based on the description just provided to you, it would be redundant to state that one could sit in awe, and actually forget about the two other aspects to a good lunch spot (these being the snacks and field partner).
Lower Steenbras Dam
At the base of the Lower Steenbras Dam lies a densely populated garden, located along the core of the Steenbras Syncline. The area is densely fractured, and the rocks have been tilted and folded. Due to the restricted access to the area to the public, the fauna and flora have largely reclaimed the land creating a picturesque ‘Garden of Eden’. We had to navigate through dense brush to find suitable outcrops to take geological readings while keeping a close eye out for the many poisonous snakes which call the area home.