We all know about Hawaii and the fact that a mantle plume, or hotspot, is creating a string of islands as the Hawaiian plate moves slowly over it. The hotspot explodes at the surface as a volcano and the molten rock that it spews out builds a new layer above the water. It flares up repeatedly so creating an entire new island.
Finally the volcano becomes quiet, while the Hawaiian plate moves on. When it next explodes again the process is repeated in a new location, so creating the string of islands that we know. Very recently there was a flare up of the volcano situated on the latest island.
Ever thought how we would experience a volcano-creating hotspot that is stationed below a part of Southern Africa for more than a million years at each site? Over the million years it would flare up now and then, but it would be touch and go whether one would have lived during that specific epoch when it flared up.
The last time a hotspot happened to erupt underneath Southern Africa was between 200 million years ago and about 90 million years ago and there were presumably dinosaurs roaming over this particular landscape at the time. The large volcanic outpourings from the massive volcanoes must have made life very difficult for them at best, and could have caused the mass extinction of dinosaurs at worst.
Knowing the footprint that this particular hotspot made on aeromagnetic maps means we can determine the path it took over Southern Africa. It came from the north along the eastern coast of Africa, swung inland over current South Africa, made a U-turn well to the north of the southern coast of South Africa and headed straight north again. The consequences of the turn it took over our part of the world are all too clear: massively thick layers of lava over South Africa, Namibia and Botswana. It is a pity that the lava of this hotspot was not well mineralized, except for the diamonds that it exploded through to surface. The lavas of its predecessor hotspots were mostly well mineralized and some of that is now buried quite deeply today.
From knowing the footprints that the different hotspots left when they visited Southern Africa we can determine that there have been at least fifteen of them so far. Each hotspot that visited left its own peculiar footprint, except for two of them that had an identical footprint (at about 3200 million years ago and at 2200 million years ago). Luckily for us it is not likely that we will have a similar arrival of a hotspot from the north for another 500 million years. It is also lucky for us that Africa has such a stable, stationary foundation that does not move. It therefore retained a memory of all the hotspots that came and went over billions of years.