Since the catastrophic releases of CO2 in the 1980s, Lakes Nyos and Monoun in Cameroon experienced CO 2 recharge at alarming rates of up to 80 mol͞m 2 per yr. Total gas pressures reached 8.3 and 15.6 bar in Monoun (2003) and Nyos (2001), respectively, resulting in gas saturation levels up to 97%. These natural hazards are distinguished by the potential for mitigation to prevent future disasters. Controlled degassing was initiated at Nyos (2001) and Monoun (2003) amid speculation it could inadvertently destabilize the lakes and trigger another gas burst. Our measurements indicate that water column structure has not been compromised by the degassing and local stability is increasing in the zones of degassing. Furthermore, gas content has been reduced in the lakes Ϸ12-14%. However, as gas is removed, the pressure at pipe inlets is reduced, and the removal rate will decrease over time. Based on 12 years of limnological measurements we developed a model of future removal rates and gas inventory, which predicts that in Monoun the current pipe will remove Ϸ30% of the gas remaining before the natural gas recharge balances the removal rate. In Nyos the single pipe will remove Ϸ25% of the gas remaining by 2015; this slow removal extends the present risk to local populations. More pipes and continued vigilance are required to reduce the risk of repeat disasters. Our model indicates that 75-99% of the gas remaining would be removed by 2010 with two pipes in Monoun and five pipes in Nyos, substantially reducing the risks.gas disaster ͉ limnology ͉ natural hazard V olcanoes can release massive amounts of CO 2 at the Earth's surface (1), and in the last 20 years natural lakes with CO 2 -rich waters have also proven to be highly dangerous (2-4). Before the nature of these gas-charged lakes was understood, sudden releases of large clouds of CO 2 gas from Lakes Nyos and Monoun in Cameroon, in 1986 and 1984, respectively, claimed the lives of Ϸ1,800 people by asphyxiation (2, 3). The gas originates from magma at great depth, but dissolves into groundwater near the Earth's surface. The CO 2 -charged water enters the lake bottoms through springs (2, 4) and accumulates in the deep, stratified lakes. Although the timing of sudden releases may be modulated by climate (5), it is now clear that continuous gas recharge into the lakes ensures a natural cycle of repeating disasters (6-8).Unlike most natural hazards, the certainty of future disasters at these lakes can be averted by directed mitigation. The solution is to degas the lakes through controlled piping of gas-rich bottom water to the lake surface where the gas is released harmlessly to the atmosphere in low concentrations. Once flow in a pipe is mechanically initiated, lift is provided by the buoyant rise of bubbly water and the process becomes spontaneous and selfsustaining. Theoretical models (9-11) indicated that this mitigation was feasible, and pumping began at Lake Nyos in 2001 and Lake Monoun in 2003 (12). However, questions still arose about the safety of this hazard miti...

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A unique humanitarian, scientific, and technical experiment is currently taking place in a forgotten mountainous region of West Africa. The experiment is on the verge of reaching its operational stage, which consists of the eradication of a “new” natural hazard; one that is potentially devastating, but which has been known for only 20 years. The Lake Nyos catastrophe, which claimed 1800 victims in August 1986, was not unprecedented. Indeed, 2 years previously a lethal gas burst, originating from nearby Lake Monoun in the same remote area of Cameroon, killed 37 people—an odd and tragic episode that went almost unnoticed. One had never before heard of Mother Nature asphyxiating human beings and most higher animals on such a scale in a single and brief non‐volcanic event.