How old are the formations at Sudwala Caves?

South African born geologist, Dr Robyn Pickering, is really fascinated by this question and has been working with the staff and management of Sudwala Caves since last 2010 to try and discover the age of the wonderful formations.

Dr Pickering studied Geology and Archaeology at the University of the Witwatersrand, in Johannesburg and then went on to the University of Bern in Switzerland to do a PhD. She is a specialist in dating cave formations, in particular stalagmites, and uses the natural radio-active decay of uranium, which is trapped inside the stalagmites as they form. This ‘clock’ is similar in concept to carbon dating but uses uranium as this has a much longer half life and rocks as old as a few million years can be dated. As they grow stalagmites record changes in the world outside the cave, mainly variations in the amount of rain and the type of plants growing about the cave.

Robyn first visited Sudwala Caves at the age of 11 with her family on their way home from a holiday in the Kruger Park. From what she can remember, Robyn much preferred the dinosaur park to the caves! Luckily things have changed over the years, and on her visit in 2010 Robyn and her field assistant/husband worked very hard collecting small samples from the various formations at Sudwala, such as the Weeping Madonna and the Screaming Monster etc. These formations are beautiful and precious, so to minimise damaging them, Warrick drilled out small 3-4cm cores, using a hand held diamond bit drill from the back of the formations. The team drilled out small cores from each one of the major formations and collected three little stalagmites from the Fairyland Chamber. All this material was then sent back to the laboratory at the University of Melbourne for dating and analysis in the School of Earth Sciences where Dr Pickering works.

The process of dating cave formations is a long slow one, so for now…watch this space!

You can read more about Dr Robyn Pickering and her research here: http://www.earthsci.unimelb.edu.au/research-area/isotope-geochemistry

The Ampitheatre

A stream of fresh, cool air from an unknown source permeates the spacious corridors, maintaining them at an even temperature of 17°C all year round.

The Sudwala cavern complex is dominated by this spectacular chamber, with a lofty corridor measuring 150 metres to its centre. The ampitheatre is 70 metres in diameter, and 37 metres high to the peak of a dome-like feature in its roof. It is named the PR Owen Hall, after the Mr Owen who bought the caves and developed them as an attraction which could be visited and appreciated by the public.

It has natural ‘air conditioning’ and makes a wonderful performing arts venue. The veteran concert singer Ivan Rebroff, who sang here in 1970, declared its acoustics equal or superior to any other.

For concert purposes more than 500 people can be seated in this dolomite chamber.

Other guests and visitors

The Ampitheatre has over the years been the venue for musical entertainments including recitals by the University of Pretoria’s Youth Orchestra, various choirs, distinguished local musicians and regular drumming workshops.

Dramatic performances have included Shakespeare’s Macbeth, Sandra Prinsloo’s production of the hilarious monologue Groet Die Grotman, and a demonstration of their cultural traditions by a family group of Namibian Khoisan.

Chambers and tableaux

As well as the PR Owen Hall, some of the most popular attractions for visitors to the Caves are the ‘Devil’s Workshop’, the ‘map of Africa’ on the Caves’ ceiling, and the magical alcove dubbed ‘Fairyland’

Geology

The Sudwala Caves are part of the Malmani Dolomite Ridge, in turn part of the Drakensberg escarpment, near Nelspruit in Mpumalanga. They are solutional caves – that is to say they were formed by natural acid in groundwater seeping through faults and joins, and dissolving rock. This most often occurs when the rock is dolomite rock and/or limestone.

The Sudwala Caves are formed in both: mostly in dolomite rock, as well as erid, shale, conglomerate, chert and limestone.

Dolomite and other rocks

Dolomite rock, or ‘dolostone’, is a sedimentary carbonate composed predominantly of the carbonite mineral dolomite (calcium magnesium carbonate – CaMg(CO3). Where the magnesium content of mineral dolomite becomes greater than its calcium content, dolomite rock is formed.

Chert is a fine-grained silica-rich sedimentary rock that may contain small fossils. Chert varies in colour, from white to black through grey, brown, greyish brown and light green to rusty red, depending on the trace elements present in the rock.

Limestone is the sedimentary rock, composed largely of the minerals calcite and aragonite – which are different crystal forms of calcium carbonate (CaCO3) – that makes up about 10% of the total volume of the world’s sedimentary rocks.

4 600 million years ago: The Malmani Ridge

The various elements of the Malmani Ridge’s rock were precipitated in successive layers during the Precambrian Period, between the formation of Earth around 4 600 million years ago and the beginning of the Cambrian Period about 542 million years ago. They formed beneath the waters of a warm, shallow sea, starting about 3000 million years ago.

The limestone in the Sudwala rock dates from a period when the sea water was concentrated enough for chemical precipitation of lime-rich material to be possible.

240 million years ago: Birth of the Sudwala Caves

The Caves themselves were formed about 240 million years ago, and in geo-morphological terms they have Karst topography, that is to say that they are shaped by the dissolution of soluble bedrock, especially carbonate rock such as limestone or dolomite.

Karst systems are typically ancient, defined and moulded by aeons of natural environmental processes. A note for the ecologically minded is that Karst systems are fragile, and even slight changes in groundwater chemistry, while not immediately and dramatically evident, may become so over a long period.

Karst Systems

A typical way for a Karst system to begin is with rain passing through the atmosphere picking up carbon dioxide – CO2 – which dissolves in the water. On the ground, the rain may pass through soil, picking up more carbon dioxide, to form a weak solution of carbonic acid – H2CO3 – which dissolves calcium carbonate such as that in dolomite and limestone bedrock. The effect on the rock is that its surface begins to dissolve, along fractures caused by tectonic shifts or other geological stresses.

Over time, such fractures enlarge as the bedrock continues to dissolve. Openings in the rock increase in size, and an underground drainage system begins to develop, allowing still more water to pass through, and accelerating the process. Ultimately, as at Sudwala, complex underground drainage systems and extensive caves and cavern systems may form.

This starts with water-filled underground chambers being created in the dolomite, and the dissolved rock being carried away in solution by the water as it finds ways to seep or flow away. The process is evolutionary: a water passage may become blocked and a chamber re-fill, until another way out is found.

The chambers of Sudwala were not originally connected. Rather, they were a sequence of caverns and reservoirs, constantly enlarging over time as rock and water got away, were replaced, and escaped again. Then a major geological upheaval occurred, the water table dropped, and the water that steadily leaked away from the underground reservoirs was not replaced. And thus we had, more or less, the structure of the Sudwala Caves of today.

That was, however, by no means the end of the Caves’ evolution. Solutional caves are often adorned with calcium carbonate formations produced through slow precipitation. These secondary mineral deposits in caves are called speleothems.

Speleothems, or cave formations

A speleothem (Greek: ‘cave deposit’), commonly known as a cave formation, is typically formed in dolomite or limestone solutional caves.

Once the carbonic acid so essential to the formation of the caves reaches an air-filled chamber, it trickles and drips down from the ceiling, where it encounters an atmosphere far less rich in carbon dioxide than the solidified sediments it has come through. Nature’s predisposition to maintain a balance induces a carbon dioxide transfer from the water into the air. The acidity of the water drops, and bicarbonate emerges from the solution as solid calcium carbonate particles, which are then precipitated by the water. The rate depends on the amount of carbon dioxide held in solution, and on temperature, among other factors.

Over time, which may span millions of years, the accumulation of these precipitates may form speleothems.

Speleothems take various forms, depending on whether the water drips, seeps, condenses, flows, or ponds. Many are named for their resemblance to objects, whether man-made or natural. Types of speleothems found at Sudwala include dripstones (stalactites and stalagmites), columns (resulting when stalactites and stalagmites meet, or when stalactites reach the floor of the cave), sheet-like flow stones, and pillars.

Stalactites are pointed pendants hanging from the cave ceiling, from which they grow. As each drop of water falls from the ceiling, the calcium content it sheds forms a calcite ring, which is left behind as the purified water drops. As this sequence is repeated the rings build up, creating a hollow tube (although as the formation develops, the centre tends to fill), eventually forming a stalactite.

If the dripping is too rapid for the calcium to be deposited, or if the water contains more calcium carbonate than can be shed in time, the surplus calcium falls in the water drop to the floor of the chamber to form a stalagmite, often with a saucer-shaped hollow, known as a splash cup, at the tip.

Curtains and walls of stalactites and stalagmites can develop, where water is dropping from a crack rather than a point in the ceiling.

The growth rate for a stalactite at the Sudwala Caves is approximately 2,5cm per century.

Sudwala’s cave formations: older than Africa

Some of the most striking speleothems at Sudwala are Samson’s Pillar (about 200 million years old), the Screaming Monster (160 million) and the Rocket (140 million). Their age has been determined by the Rhebedium Strontium test, which measures the radioactive decay of cave formations.

To give an idea of the antiquity of these formations, at the time they began to be formed, between 510 to 180 million years ago, our planet still consisted of two supercontinents, one of which – Gondwana – included most of the landmasses in today’s Southern Hemisphere, as well as the Arabian Peninsula and the Indian subcontinent, which have now moved entirely into the Northern Hemisphere.

Biology

Fossils: Collenia

In the Precambrian period all the early animals were soft bodied and thus did not fossilise well. However, primitive plant fossils called Collenia, dating back 2000 million years, may be seen in the Sudwala caves. They were a type of blue-green algae, tubular shaped and about 2cm long, which used to float on the ocean. They were one of the first plants to produce oxygen safe enough for our prehistoric ancestors to breathe. The plants would get trapped among the rocks at high tide, and get mixed up with sand and silt, before the whole lot became compacted in the rock. In time, successive layers accumulated on top of the previous ones.

Cave animals

Two factors strongly preclude the possibility of finding true cave animals in the main Caves:

- The Caves are extremely dry compared to when they were developing.
- The tourist traffic, and required illumination, drive cave life forms into more remote and inaccessible areas of the Caves.

Horseshoe bats

The only organisms that can be seen by tourists in the Caves are insectivorous bats of the Horseshoe species (Rhinolophus Londeri and Rhinolophus Hildibrandi). There is a colony of about 800 throughout the cave system. They leave the caves at about 7:00 pm each evening to feed, mainly on mosquitos. They fly at an average speed of 20kph in a radius of 200km from the Caves. By the time they return, at about 4:00 am, each will have consumed roughly its own body weight, or about 800 insects per bat. The bats live for about 24 years and do not carry rabies, although they do have lice, which help to keep them clean. They present no threat at all to humans.

Algae and ferns

The algae and ferns in the PR Owen Hall, and along the tourist trail, are not to be considered as part of the biology of the Caves. They exist only because of the lights in the Caves. From the viewpoint of the professional speleologist their presence is undesirable, since the green stain contaminates the true colour of the formations. Unfortunately it is practically impossible to prevent the introduction of spores and seeds into the Caves as long as they are remain a tourist attraction.

Small fry

Centipedes and rodents can be seen occasionally in the entrance zone.