Geology

Thank you to Dave Mourant of the Overberg Geoscientists Group for authoring this page.

Every rock has a story…

Rooiels is a fascinating and beautiful village, sitting between the mountains and sea. But what has contributed over geological time to make it such? The immediate view highlights two things: the most obvious is the dominating Klein Hangklip mountain and cliffs. Also the lower flatter areas on which most of the village is situated.

Google Earth image: Rooiels from the sea looking east

Formation Of The Area

The Gondwana supercontinent formed some 600 million years ago. As what is now South America closed in and docked by the West Coast, sediments were laid down in what we call the Adamastor Ocean. These sediments became rock that we can see as we drive along Clarence Drive going to Gordon’s Bay. They are called the Malmesbury Group. Malmesbury Group rock is visible at Kogel Bay and at Blousteen.

500 million years ago a rift opened between the Falklands plateau and the southern coast of Africa. A shallow sea formed – this was the repository for clean white sands which then were buried, and hardened into the Table Mountain Group rocks.

330 million years ago the rift started to close, and this folded the sedimentary rocks.

290 million years ago, continued compression between the two land masses continued, forming the Cape Fold Mountains we see around us.

Then, about 128 million years ago, the South American and Falklands land masses started to break away to the south and west, forming the continents as we see them today. This tension led to the exposure of the folded Table Mountain rocks and some breaking of the rocks on a more local scale.

Topography Of The Area

The topography was then subject to erosion – mainly by weathering. The Table Mountain group contains not only the very hard sandstone that forms the high ridges, but 2 other types of rock that can be seen lower down. These were formed under different conditions.

Immediately above the Peninsular formation which forms the base of the Table Mountain Group is a rock laid down by glacial action. It is called the Pakhuis Tillite and was formed as glaciers carved their way down valleys eroding the underlying rock and carrying it along. When the glaciers reached the sea the rock was dropped as they melted. That forms the grey substance of the Tillite, but, distinctively, there are numerous white quartz pebbles that were much harder, and remain. Some of the larger pebbles even have scratch lines where they were transported by glaciers. Tillite can be very easily seen on the Aasbank and Sea Farm peninsulas.

Immediately above the Tillite is a much softer rock called the Cedarberg Shale. It was deposited as mud in quiet, deeper water. It forms a rock which is much softer and more easily eroded. However, it contains more nutrient minerals and water than the sands. Thus it usually has more verdant Fynbos. Shale makes the Hangklip Valley in Pringle as it has been eroded to form the valley. The Tillite forms the seaward side of the valley and is very accessible. Notably as one walks up the valley there are many small white pebbles on the path, eroded from the Tillite.

This image shows the layers of the Table Mountain Group above the Buffels dam between Rooiels and Pringle Bay. It can clearly be seen that the shale forms a lower relief and has more greenery.

The main valley along which the R44 road runs between the villages follows a weakness in the rock formations caused by a fault or movement. This major move was caused by the tension during the splitting up of Gondwana and the Southeastern movement of the Falklands Plateau. All these continental moves are initiated and powered by plate tectonics, caused deep in the mantle of the Earth.

There is another fault line that greatly affects the topography and environment of the village. This is one line of weakness that has been eroded by the Rooiels river to form the course of the valley and to create the conditions that allow the beach to be situated at its estuary.

The Coastal Platform

The coastal platform forms the areas on which most of us live. These are the flat areas between the mountains and the sea, sometimes seen as bare rock and sometimes covered in sand. All the villages in our area, and indeed extending to Hermanus and beyond are based on the flat area near the sea, though there are different elevations.

Rooiels from the air (piloted by Gavin Lundie)

Greater Hangklip area from the air (piloted by Gavin Lundie)

A World Under Water

So why do we have these very welcome platforms?

They are referred to as “Wave Cut Platforms”. As the name implies, they refer to a time when the sea level was much higher than now. This was probably during the last warm interglacial period some 125-150 thousand years ago. Back then, our mountain range would have been sea cliffs, and the areas where we live now would have been underwater.

There is further evidence of this in Rooiels itself. Heading toward Gordon’s Bay, just over the river and before the first view point there is an outcrop of a sand dune on the right-hand side. This is a marine dune, as it contains shell fragments and sponge spicules. The loose rock fragments and debris (known as talus deposits) have fallen from the cliffs in recent times, or may have accumulated some 35 million years ago, and become ‘rubified’ i.e. stained with iron that has been dissolved from the eroded rocks above.

This deposit is 30m above the present sea level, proving higher historical sea levels.

Rooiels Today

So let’s look at how all these events and processes have intersected to make Rooiels the beautiful village it is, in such a stunning setting.

As we have seen, the topography and soil types depend largely on the underlying geology. The cliff faces and talus slopes consist largely of sandstone. This does not supply a lot of nutrients, but the slopes have a covering of fynbos which has adapted to the nutrient-poor conditions. While this substrate does not support a huge variety of fynbos, the specialised vegetation is certainly enough to stabilise it.

The wave-cut platform that fringes the seaward side of the mountains has many small pockets of differing environments as it is not a completely flat plain. There are areas that contain remnant ancient dunes and some hollows with wetlands and vleis. There’s also evidence of some higher-level platforms that display slight variations as well. The Rooiels river valley is well watered and contains much sediment brought down by the river. This is a very good, if restricted, environment for larger trees and shrubs.

The main valley behind the ridge along the R44 is one of the best fynbos environments in the region. It is floored by alluvial soils eroded from the surrounding mountains and the differing rocks have provided a much better soil. The river or streams running through it provide much more constant water than the “flash floods” off the mountain faces.

The area from Rooiels to Betty’s Bay is magnificent fynbos, and has been helped by the efforts of the various hack teams in the area.