Put on the air
Disasters rarely announce themselves. It is therefore a stroke of luck if sufficient protective measures can be taken in good time. And all the sadder when they fail due to a lack of funding.
15. August 1984. 37 people lie dead - suffocated - in their homes on the shore of Lake Monoun in north-west Cameroon. Wild speculation about the cause of death circulates, from secret chemical weapons testing to a terrorist assassination. Scientists, after much deliberation and analysis, believe the lake to be the culprit.
26. August 1986. A catastrophe occurs just a hundred kilometers away: 1,700 people and countless animals die at Lake Nyos, again from suffocation. For the researchers, the event brings the sad confirmation of the cause: In both cases, huge clouds of carbon dioxide and methane had collected at the bottom of the lake and, for unknown reasons, had suddenly risen to the surface in a fountain - like an overflowing champagne bottle. The gases then spread near the ground, taking the breath away of people and animals alike.
"Limnic eruption", experts called the process the following year at a conference. The reference to volcanism is deliberate, after all, such a gas ejection is as unpredictable and sudden as a volcanic eruption. Both lakes are in a volcanically active region where they fill former craters. The gas comes from the subsoil, where methane, carbon dioxide and co are still escaping from magma chambers. They then flow into the lakes with the groundwater.
In most cases this is not a problem: as long as the water bodies of the lakes are regularly overturned, the gases come to the surface in harmless quantities and escape without endangering life. However, at Lake Monoun and Lake Nyos, the maars had literally exploded. Because there is no upheaval here: the lakes are layered in a stable manner, and there is no exchange between the top and bottom. In this way, a gas supply could accumulate in the depths over a long period of time, which eventually reached lethal dimensions.
But how should the people in the region be protected from further outbreaks? The idea was soon born, but due to financing difficulties, the implementation then dragged on for years. And this despite the fact that time was of the essence: Gas reserves that are larger than the quantities released during the eruptions have long since accumulated again in the depths. Since 2001 on Lake Nyos and since 2003 on Lake Monoun, however, deep pipes have been allowing the gas to escape in a controlled manner - and this by their own drive: After a pump had gotten the whole thing going, the pressure at the depths now ensures that it is constant a meter-high fountain brings relief.
It was a delicate experiment for the scientists and engineers involved: would the constructions they calculated work as planned? Finally, in a preliminary test, a pipe shot up again, shocking everyone. Or would their intervention possibly lead to the worst - a disruption of the stable stratification of the lakes and thus to another deadly eruption?
George Kling of the University of Michigan and his colleagues can sound the all-clear. The researchers have been following developments in the water bodies since the pipes were installed. And as the measurement data show, the stability of the stratification has even increased as a result of the controlled withdrawal of CO<sub2 - so there is no reason to fear a renewed eruption through the lines. However, such an event is not excluded, after all, subterranean tremors can also bring the unstable balance into devastating swaying.
And the danger for the population is still great: The previous pumping campaign has reduced the gas reserves in the lakes, but so far only by 12 to 14 percent. However, as extraction increases, the pressure at depth falls and the replenishment slows down - and with it the amount of gas that escapes.
Kling and his team calculated a forecast for the future using a model based on values from the last twelve years. As a result, the vent used in Lake Monoun will remove about thirty percent of the total gas supply before the replenishment from below simply outweighs the vent upwards. In Lake Nyos, the balance is even more meager. According to the researchers, just a quarter of the gas volume will escape here by 2015.
What to do? Kling had asked for several pipes from the start - and can now back this up. Because if the researchers simulated the future scenario of five pipes on Lake Nyos and two pipes in Lake Monoun, the opening of which should also be deeper than at present, this would probably release 75 to 99 percent of the dangerous gases into the air in a controlled manner by 2010. The risk for the local people, some of whom have returned to their villages because they find fertile soil there and now even fish in the lake, would drop dramatically. The only question that remains is whether the funding battle will be decided before the next outbreak.
