Africa, nuclear power and earthquakes

Posted on May 13, 2011


The massive earthquake off the coast of Japan in March triggered a ten-metre tsunami wave that swept up to 10km inland, devastating whole towns and villages. It also smashed into the Fukushima nuclear power plant causing widespread — and still ongoing — concern about the safety of such plants.

This tragedy gave anti-nuclear power advocates an ideal platform around the world to trumpet their cause. It also put the still considerable pro-nuclear lobby into high propagandistic gear and has triggered debates about the hows, whys and wherefores of earthquakes. Japan and Christchurch in New Zealand alone have this year shown what devastation these shifts in the earth’s surface can cause.

But what has this to do with countries such as landlocked Zambia — and Africa as a whole? The truth is: a great deal. Not only because nuclear power is still being seriously mooted as a viable alternative global source of electricity, but because, like the continent, the African land mass is part of the the earth’s hard “crust”. This relatively thin, often brittle, surface layer of our world floats on a hot, semi-solid mantle that sits atop a molten outer core of magma near the centre of the planet.

The hard crust extends beneath the oceans of the world, and has many cracks in it, known as fault lines. These occasionally slip or slide against one another, causing upheavals on or near the surface. And there is nothing new or unusual about this. Every year there are roughly 50,000 earthquakes around the world that are strong enough to be felt by people near them. However, fewer than 100 are strong enough to do any great damage — and many of these occur in remote areas or far out to sea. But, on an average of about once a year, somewhere on the earth, there is a very powerful slippage in the earth’s crust that causes damage over a wide area. The slippage that resulted in the latest Japanese earthquake and tsunami, for example, occurred in the sea, 134km from the coast of Japan.

In the past 30 years, across the African continent, there have been more than 50 such events that have resulted in more than 23,000 known deaths and damage that has never been quanitified. As regards southern Africa, Chris Hartnady, an internationally recognised and Cape Town-based expert on geotectonics, says it is not a matter of if, but when, a major event will occur somewhere in the region.

The strengths of these natural disturbances vary and are measured by the Richter scale with each “notch” on the scale representing ten times the strength of the previous one. So a Force 7 earthquake would be 100 times more powerful than a Force 6. The earthquake that devastated Christchurch in February measured 6.3 on the scale, but its epicentre was just 10km from the city’s centre. Seismologists are still arguing about whether it was technically an aftershock following the 7.1 strength quake that struck the city in September last year. The argument arose because the latest slippage occurred along a previously unknown fault line, highlighting the fact that scientists are still not fully aware of where all the fault lines are.

But the fault lines running down and across Africa are fairly well mapped. Africa’s Great Rift Valley, for example, is a depression in the earth’s surface bounded by two parallel fault lines that extend from Syria to Mozambique. Almost imperceptibly, the rift valley is widening, causing, as a result, a number of volcanic eruptions and generally minor earthquakes in regions north of the Zambezi. Evidence of this can be seen in the many hot springs and more than 30 active and semi-active volcanoes along the length of the rift, many of them in and around Kenya.

There have also been a number of earthquakes in the Lake Tanganyika region, some of which have been felt in Zambia. In many instances, areas between or on fault lines also result in depressions — in valleys that provide courses for rivers and that tend to be seen as the ideal places to build dams. The Kariba dam, like the Hoover in the United States or the Koyna Dam in India and the Kremasta Dam in Greece have all experienced what is known as “reservoir-induced seismicity” (RIS) events. This is assumed to be the effect of the weight of water on an existing fault, causing a movement beneath the earth’s crust resulting a series of sometimes major tremors on the surface.

Several years ago, geologists at South Africa’s University of Cape Town raised fears about the huge Katse dam in Lesotho, the second largest and deepest dam in Africa, that sits on a known fault line. The geologists maintained that millions of tonnes of water resting on a crack beneath the earth’s surface could trigger a major slippage. Engineers agreed that there could be some slippage, but pointed out that the 185m high dam was built to withstand an earthquake measuring 6.6 on the Richter scale. Anything more powerful that this was “extremely unlikely”.

It is this question of doubt that has strengthened the argument of the anti-nuclear lobby. People such as South African campaigner Mike Kantey point out that nobody knows exactly what the full extent of the danger is. Before getting into the question of the cost of the disposal radioactive waste or of the decommissioning of nuclear plants, the objectors point to the possible consequences of serious accidents; of “melt downs” and radioactive leakage.

Both of these, they maintain, can come about as a result of human error or by a natural disaster such as an earthquake and an accompanying tsunami. Looked at in this way, Africa’s only nuclear power plant — Koeberg, across the bay from Cape Town — is “an accident waiting to happen”.

Not so, say the supporters of nuclear power. And they point out that Koeberg — it came on stream in 1998 — is of a more modern design than Fukushima, with a range of safety procedures that did not exist when Fukushima went into operation. Even a 10-metre tsunami such as the one that crippled the Japanese plant, would not, they maintain, cause serious damage to Koeberg. However, with a known fault line just 8km off the coast from the power station, a slippage could cause a large wave and this would wreak havoc in South Africa’s “Mother City”.

Much of the land on which the city’s foreshore development is built is reclaimed from the sea and is barely above sea level. A huge wave, moving east across Table Bay, might not cripple Koeberg, but it would almost certainly flood the Milnerton suburb and lagoon before being channelled across the low-lying areas of Paarden Island and into the city itself. “It would cause very severe disruption,” admits University of Cape Town (UCT) oceanographer, Geoff Brundrit.

However, UCT geologist Ake Fagereng notes that the Milnerton fault line is “not very volatile”. But he also points out that activity has occurred in the past, with the last major quake in this area taking place in 1809. Another strong — 6.1 — earthquake struck north-west of Cape Town in 1969 resulting in the deaths of 12 people and considerable damage to 70 per cent of the buildings in the town of Tulbagh. But earthquakes of even more moderate magnitude can cause tremendous damage and loss of life. Africa’s worst earthquake disaster, for example, was the quake that struck the Moroccan coastal town of Agadir in 1960. It measured just 5.7, but killed an estimated 15,000 people.
Hartnady and others are now calling for more education about these occurrences and for better preparation in terms of building regulations and emergency measures in the case of earthquakes. The current focus, because of the Japanese experience, is on Koeberg, which engineers for South Africa’s electricity parastatal, Eskom, maintain is built to withstand a force 7 earthquake with its epicentre immediately under the plant.

This assurance has not impressed Kantey and other protestors. And, as local geologist Nik Wullschleger has pointed out: “Fukushima shows that, in the final event, anything can happen, despite risk assessments.” And the anything that could happen is anywhere that the fault lines run.

Posted in: Environment