BLAST Vredefort Dome Tours

01/11/2026

01/11/2026

CHASING RABBITS THROUGH GEOLOGICAL TIME
Origins of Sasol's oil and the meteorite crater

* Only the picture is AI

When I was a young upstart teaching at Rhodes University, Saturday night's entertainment for postgrads was driving on bushy back roads in the hunt for rabbits. The trick was to get drunk first and then, stumbling along in front of the pick-up's headlights, try to grab a startled veld hare by the ears without falling and getting run over.

No harm was ever done to hares or hairy seventies hippies but it was agreed all around that this was exhilarating exercise and a good way to sleep it all off afterwards.

Since I became a writer I've realised it's like catching - or failing to catch - rabbits on dark twisting roads. Especially if you're writing up research for a popular audience, ideas spring up everywhere and seem very exciting: you just have to lay hands on them.

Right now I'm busy with the concluding chapters of my book on the world's biggest known meteorite impact crater, the Vredefort Dome. The section, called The Dome in Future, reaches well beyond Dome studies as such into crater research literature in general that's both speculative and controversial.

One idea that I covered in a previous post ("How deep did it go?") deals with the idea that massive impacts may have helped to build Earth's continental plates. Another, which is sketched out here, holds that impacts have created fractured landscapes that trap hydrocarbons (peat, which can turn into coal or gas fields).

The 2 billion year old crater forms a landscape that later hosts steamy tropical swamps in hollows and faults. The researcher who prompt this line of thinking of me is Alaskan geologist David Buthman who came to the Dome last year out of curiosity. We blew his mind on a deep mine visit to Moab Khutsong near Klerksdorp: the deepest single shaft descent on Earth featuring a terrifying, drenching drop of more than three km straight down packed in a crowded cage. Water pours down the shaft as you drop.

David was duly impressed and looked wrung-out on reaching the surface after a lengthy trek in the hot tunnels. There's gold down there, not coal, but his interest was in the fracturing of rocks by the tremendous shock of impact. On the North Slope of Alaska he searches for hidden meteorite craters and then drills their margins to find oil and gas. He's been fairly successful in this new field of prospecting.

So I put it to him that the coalfields of the Sigma mine and Coalbrook near Sasolburg could have formed in the landscape left by the asteroid blast. Like a good scientist he was non committal but did agree it was plausible.

Further reading of scientific papers has shown that there is some substance to the idea. Sasolburg is where South Africa began making liquid gas, petroleum and various waxes as a strategic government project in 1956. Using the prewar German chemical Fischer-Tropp process on coal from the Sigma mine, the country sought self-sufficiency in fuel production.

The story of Sasolburg is a remarkable intersection of geology, German chemical science, South African mining enterprise and government industrial policy. It began long before apartheid, although the apartheid government ultimately built the first large-scale plant.

Sasol has been one of those rabbits that spring out of the ground as writing unfolds. It's not directly relevant to the impact story but is fascinating it its own right and does suggest there's more to the eye than just a big bad crater. My training in journalism and later popular science writing helps to tell the story with all its spin-offs.

The larger theme is geological inheritance: how a landscape shaped by events billions of years earlier may have influenced the distribution of resources that ultimately made Sasolburg possible. Buthman's observations can provide a thought-provoking concluding connection to modern exploration methods, without presenting an impact-related origin for the coal as established fact.

The Sasolburg coal belongs to the great Permian coal-forming episode of southern Africa, roughly 280–250 million years ago. During this period, southern Africa formed part of the supercontinent Gondwana.

The landscape was very different from today's dry Highveld. Large low-lying areas accumulated sediments, while wetlands and vegetated floodplains developed in low lying environments. Dead plant matter built up without completely decomposing. Then rivers, floods and muddy deposits covered the organic layers. Over millions of years, increasing burial, pressure and temperature transformed organic matter into coal. The coal seams survived within the sedimentary rocks of the Karoo Supergroup.

The critical geological point is that coal did not form because of volcanic activity or the Vredefort meteorite impact. It formed through ordinary sedimentary and biological processes hundreds of millions of years after the Vredefort event. The coal deposits near Sasolburg were particularly attractive because of their scale and accessibility, although much of the coal was relatively low grade.

Although the impact had nothing to do with coal, there is a relationship between Sasolburg's coal and the Vredefort Dome.
According to the geological review by Hancox and Götz, the Sigma coal sub-basin lies along the western side of the Vereeniging–Sasolburg coalfield. Its western geological boundary is formed by pre-Karoo rocks of the Vredefort Dome, while an ancient ridge of Ongeluk volcanic rocks separates it from the Cornelia sub-basin to the east.

The coal accumulated in an irregular landscape of older rock, with valleys and ridges influencing the thickness and distribution of the deposits. The Vredefort impact did not create the coal, but the much older geological architecture of the region helped shape the terrain upon which the coal-bearing Karoo sediments were subsequently deposited.

In other words, the geology of the Dome and the coalfields is not entirely independent. There is a relationship through the ancient basement landscape, even though the two geological events were separated by approximately 1.7 billion years.

After much stumbling, I did lay hands on this particular rabbit.

JOIN ME FOR AN ILLUSTRATED DOME TALK OR TOUR. Prof Graeme Addison +084 245 2490. https://vdome.co.za

16/10/2026

THE ROCK THAT SEEMS ETERNAL
It isn't but it keeps recycling and returning

I am fascinated by a very common rock that seems hardly exceptional because it is found almost everywhere. Its name does not actually mean “hard”, as is sometimes claimed, but comes from an old word meaning “grain”.

But in English we often use its name as a synonym for hard and unyielding.

It has a grainy, crystalline appearance. It may be pink, grey, white or faintly greenish, speckled with pale quartz, white or pink feldspar, and flakes of black mica. Stone merchants also sell polished rock as "dimension stone" because it is cut to certain sizes.

It was born deep within the continental crust when molten rock intruded upwards and cooled very slowly, allowing its interlocking crystals to grow. Great underground masses formed batholiths and smaller intrusions. Over immense periods, erosion stripped away the rocks above them and exposed these ancient foundations of the continents.

Cut into slabs, the rock is prized for polished kitchen worktops, floors, walls and monuments. Far from being impossible to carve, it was shaped with extraordinary labour by the ancient Egyptians into statues, obelisks and enormous columns. Its hardness made such work difficult, but also made the finished objects endure.

Yet this seemingly everlasting rock contains the seeds of its own destruction. Rainwater, made mildly acidic by carbon dioxide and substances in the soil, enters the joints and attacks the feldspar, slowly changing it into soft clay. Mica also alters, while the tougher quartz crystals are freed as grains.

Much of the pale sand on beautiful beaches is not the rock itself, but quartz released from rocks like this and carried by rivers to the sea.

The rounding begins underground. Water reaches a buried block along its cracks and attacks its corners from three directions, its edges from two and its faces from one. The corners decay fastest, then the edges, until a once-angular block becomes a rounded corestone enclosed in softened, crumbly material.

When erosion carries that material away, immense boulders appear at the surface, sometimes in large numbers like the heads of a crowd.

The broad, whale-backed domes and rounded shoulders form in a related way. As kilometres of overlying rock are removed, pressure on the buried mass is released. The exposed outer layers expand slightly, fracture roughly parallel to the surface and peel away in great curved sheets, rather like layers coming off an onion.

Hence onion-skinning to describe roundish plates of the rock.

Weathering softens the forms further. Small shelters, fissure caves and spaces beneath fallen boulders may develop, but not the extensive solution caverns found in limestone.

Under great heat and directed pressure, this rock may be transformed into gneiss. It does not usually melt. Instead, its minerals recrystallise, flatten, stretch and separate into pale bands rich in quartz and feldspar and darker bands rich in mica or other dark minerals. Folding and shearing may bend these bands into the lovely stripes, waves and swirling patterns that make polished gneiss look almost like frozen movement.

There is something else remarkable about it. Although it looks permanent, it participates in a vast cycle: magma becomes crystalline rock; rock decays into clay and sand; sediment is buried and transformed; and deep crustal material may eventually melt again. A kitchen worktop and a grain of beach sand can thus be different moments in the life of the same planet.

I fell in love with this rock because so much of my favourite landscape is made from it: the ancient central uplift of the Vredefort impact structure. The name “Vredefort Dome” can be misleading. The feature is not confined to the town of Vredefort, and today there is no great dome standing above the countryside.

The original uplift has been profoundly eroded, leaving a largely flat central core surrounded in places by the rugged, upturned ridges of the Dome Bergland. It is not an igneous plug but the exposed root of a colossal rebound structure, raised from deep in the crust when the meteorite struck more than two billion years ago.

What is this rock called?

Come to the Dome to see it for yourself. Talks, walks and guided drives with Prof Graeme Addison.
+27 84 245 2499. Https://vdome.co.za

09/10/2026

UNIVERSITY DOME TOUR

The mighty Vredefort Dome meteorite impact site draws hundreds of school and varsity students who come to learn what the fuss is all about.

Today they came, they saw, and they hiked the new Dome Geotrail. 170 Geography students. Geography is not exactly geology but it includes an understanding of Earth processes, and these students from North West University had a day of it.

The town of Parys is the big drawcard with all its tourist facilities. The name Vredefort Dome is a bit of a misnomer because the crater is not at Vredefort and it isn't a visible dome. Vredefort is merely closest to the centre of what's now gently rolling platteland grassland.

Geologists call the immense plug of granite that fills the crater centre a dome.

This and much more is explained and illustrated in talks and videos. Our team also opens up discussions of Vaal River ecology and pollution (the river flows right through the Dome) and throws light on the human history of the region - especially the San, Khoi and Tswana before the arrival of whites. Lastly we do a fun mapping game to show how to orientate maps by the compass.

These are things geographers need to know. The afternoon is spent hiking the Geotrail, looking at exposed samples of rocks from the moment of impact.

All in all this is an educational adventure - a Day in the Dome that removes any idea that the crater could be an ancient volcano. It isn't. It is a "star scar" on the Earth created by the biggest known impact - a rock estimated to be between 15 and 24km in diameter, that struck here 2 billion years ago.

That's twice the size of the one that killed the dinosaurs: the second largest known impact crater at Chicxulub in Yucatan.

Bring your University or school group to experience this awesome place!

Prof Graeme Addison: 084 245 2490 . Https://vdome.co.za

07/10/2026

SOME CRATER, SOME GHOST!
We don't know what we don't know

Winston Churchill once mocked those who had predicted Britain's rapid defeat in 1940. French generals had warned Churchill that England would have its neck wrung like a chicken. Eighteen months later, with Britain very much alive, Churchill retorted: “Some chicken! Some neck!”

Something of the same thought occurs when you look at the Vredefort crater. It's a ghost of its former self. Nearly two billion years of erosion have stripped away the crater walls and much of the landscape created by that colossal impact. Yet the ghost is still enormous.

Some crater. Some ghost!

What we see today is not really the crater at all, but its deeply eroded roots. It deserves to rank with Kilimanjaro and the Grand Canyon as a Wonder of the World - and yet it is far less well known. It is also quite difficult to understand if you only look at the mountains of the Dome Bergland.

What are they? How did they emerge from the catastrophe? They are not one of the original crater rings.

Situated in the heart of South Africa just south of Johannesburg the crater - what remains of it - marks what UNESCO says is the site of the “world’s greatest single, known energy release event.” It also calls Vredefort the oldest, largest and most deeply eroded complex meteorite impact structure on Earth.

Because the crater tells an obscure story, some incorrect myths have grown around it. While it appears to have three "rings" these are not the true multi-ringed crater as it originally took shape. And while the bottom half of it disappears this is not because it is slanted underground due to the angle at which the asteroid struck.

Also, this is by no means just a surface feature. Its shock effects stretch far and wide and deeper than some blip on the face of the Earth. It is a monster of a thing.

The truth is we know too little about it because it happened so long ago. Much that is said in the orthodox scientific version of the impact today is open to doubt as more research findings turn up surprising facts.

Some things are well established: an impact occurred at about 2.02 billion years ago; it produced shock metamorphism, shatter cones, impact melt and enormous structural deformation. What remains uncertain includes the original crater diameter, projectile size and velocity, detailed crater morphology and some consequences of the event.

What really formed when a massive rock between 8 and 24 km slammed into the remnants of the primitive continent, Vaalbara, some 2 billion years ago? Vaalbara is a hypothetical reconstruction of what was possibly the first continent in earth stretching between what is now southern Africa and Australia.

My own readings of the latest papers - and I am no geologist but rather a well practiced popular science writer - suggest that the impact may have had a lot to do with the remodelling of the Kaapvaal Craton. The Craton is the vast shield of rock lying at the centre of the subcontinent, and the crater happens to be more or less in the centre of it.

The impact profoundly deformed and exposed the Kaapvaal Craton. The craton was already ancient when Vredefort struck it.

Like all questions in science there is much detail unproven. Half of the crater rim seems to be missing in the southeast because the rocks that were there before impact were softer - and have eroded more quickly - than the much harder Witwatersrand quartzites to the northwest.

Much of the southern/southeastern structure is also covered by younger Karoo-age sediments and dolerite, rather than simply having disappeared.

It's not my job as a mediator between scientists and the public to decide questions, but to report the state of play.

The so-called three rings of the crater which we can still partly see today are exposed from deep down as impact-uplifted, tilted/folded geological strata. The resistant quartzites of the Witwatersrand have stood up particularly well under subsequent erosion.

Glaciation and later erosion modified the landscape, but they did not create those geological rings from scratch. They are what a moving field of ice left behind as it ground down the original landscape.

The rings we see are genuine expressions of the impact structure, but they are not surviving crater walls. We are looking at an erosional cross-section through the deeply exhumed structure left after two billion years.

That's nearly half the age of the Earth! The geomorphology - changes to the planet over time - are mind boggling and difficult to follow. Again, the evidence is sparse and debatable.

So what I do in my Dome presentations and tours is not sugar-coat the complex story that at times has caused bitter divisions amongst the experts. It all deserves to be told in summary form and with colourful examples.

We have the body of the blast victim but the rest is a whodunnit - and how.

Come and see it for yourself. +27 84 245 2490. https://vdome.co.za

28/09/2026

RAFT CAMPING IN THE DOME
First 2-night trip of the season

We're two days on the beautiful Vaal in the Vredefort Dome world heritage site. This is the only major river on Earth that flows right through a meteor crater - and it's the biggest known crater at that.

Our camp overlooks the Spinning Rapid, a smooth flow of current that's great for swimming. The water accelerates and carries you buoyed up by your floatation (PFD or "lifejacket" into the calm eddies below.

We camp on islands in the river but you can choose bed-and-breakfasts. Trips may be one, two or three nights. The rafts are what you choose: two seaters, a social paddle rafts, and passenger oarboats.

We had a braai last night and plan to enjoy a chicken potjie tonight with potatoes baked in their jackets and fresh salad. The tarp we put up on landing at camp protects us from dew and any drizzle. Everyone sleeps warm in their tents with mattresses.

It's a great outdoor experience, especially for youngsters with their parents.

Trips run from September to April on a river that is always reliable. We need eight to make it viable (max 14) but if your number is smaller you can join a scheduled trip. Discounts for couples, families and groups, with special packages for teambuilds.

And, of course, the river is exciting. Vaal rapids are moderate and no experience is required. Join The Riverman and our professional guides for a memorable two or three days rafting through a breathtaking landscape.

084 245 2490. https://riverman.co.za/