Those rocks and stones

2008-08-07 00:00

We are at the end of our 1,1 billion-year journey. We started out on the oldest basement rocks of our province, exposed in the Valley of a Thousand Hills, and have travelled up through almost a quarter of the age of the Earth.

This is all very well, but other than a romantic waltz down the millennia, what effect does this all have on our everyday lives?

Well, last week, amid the thorn trees and aloes and beautiful vignettes of a river overhung by palm trees and colonies of weaver birds, was a water well recently drilled for the KwaZulu government. An estimated 35 000 litres of water per hour was gushing from the well head — a plastic bucket wired over the top to prevent a fountain of water spurting into the azure sky.

For the local women, this was heaven-sent, beautiful, sweet, fresh water — gone now were the days of filling water containers from the turbid river further down the hill.

These artesian conditions, as they are known, cause the water to be driven out of the borehole by high hydraulic pressures within the rock mass. This borehole, part of a programme to augment the water supplies to the rural communities of the province, had been set out by an Earth scientist — well-schooled in geological principles and with an eye for the terrain and the rock structures of the area.

Geology affects our lives in fundamental ways. The computer on which this is being written is made essentially of plastic — a by-product of the petroleum industry. The silicon chips and semiconductors which make up its electronic wizardry are products of mining and ore benefication.

Much of the car in which you travel to work is derived from petroleum products —the plastic dashboard, seats, head cloth, instruments, steering wheel and tyres immediately spring to mind, never mind the fuel which powers it.

The steel for the body- work probably comes out of the banded iron formations of Sishen, the aluminium from bauxite mines of Australia and the platinum in the catalytic converter from the mines of the Bushveld Complex.

You will probably be reading this article within the confines of four walls made up of brick, cement, concrete or stone. All are geological materials with their own particular properties and a good understanding of geology is required for their manufacture.

The tsunami of the Day of Goodwill, December 26, 2004 was the result of movement along tectonic plates, acting as a giant piston to send a deadly wall of water across the oceans, devastating coastal regions in Indonesia and Thailand and as far away as Somalia. Volcanoes disastrously erupt, perhaps the most famous being Vesuvius and the associated destruction of Pompeii and Herculaneum.

Mount St Helens blew her top spectacularly in 1980 and every day Californians, Japanese and Turks live with the threat of earthquakes. To understand, predict and reduce the effects of these natural disasters requires an understanding of geology.

Perhaps a little more mundanely, but no less important to our ongoing wellbeing, is the application of geology to the built environment. The Gautrain project received a bad rap due to a “collapse” in Oxford Road a few weeks ago.

Discussions with people involved indicate that it was due to conditions not directly attributable to the tunnelling operation going on below.

To prevent collapse the rock mass needs to be well understood by the tunnel engineers. The spacing and orientation of natural joint systems, faults, soft and weathered areas and the occurrence of groundwater are all factors which impact on the stability of a tunnel.

On the northern section of the Gautrain the piers for the overhead rail lines are founded on dolomites, prone to solution cavities and sink holes. A detailed drilling programme and borehole radar surveys allows the designers to peer into the rock to see if there are unwelcome cavities which may impact negatively on the project.

Then there are the large rail and road cuttings and embankments to be constructed, and similar to the tunnelling operations, they require an understanding of the geological materials through which they are being driven. Locally we have had ongoing problems with the stability of Town Hill and repairs are currently under way to repair a portion of the road which failed late last year after heavy rains. Whether this is due to a slip plane forming at the toe of the slope remains to be seen.

Geologists therefore wear many hats, whether they are exploring for ore bodies, mapping the ore-bearing reefs of a gold mine, setting out groundwater boreholes, finding limestone reserves for cement production, or determining the engineering properties of the rock on which a skyscraper is to be founded.

In short, modern society cannot exist without their services and next time you consider the origins of any object of the modern world, remember that in all likelihood a geologist has been involved at some stage in its production.

• Allan Davie is a consulting geologist and may be contacted at 082 926 0626 or e-mailed at geologist@netactive.co.za for all things geological.

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