Degassing the “Killer Lakes” Nyos and Monoun, Cameroon

Halbwachs, Michel; Sabroux, J. C.; Grangeon, Jacques; Kayser, Gaston; Tochon-Danguy, Jean-Claude; Felix, Alain; ́eard, Jean-Christophe B; Villevieille, A.; Vitter, G.; Richon, Patrick; Wüest, Alfred; Hell, Joseph Victor

doi:10.1029/2004eo300001

Cited by 79 publications

(38 citation statements)

References 9 publications

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“…1). The pipe installed in Lake Nyos operates with a maximum CO 2 removal rate of Ϸ7.50 ϫ 10 8 mol͞yr when withdrawing from 203-m depth, which is similar to the 8 ϫ 10 8 mol CO 2 ͞yr reported with different methods of estimating gas concentrations (12). The degassing noticeably lowered total gas pressures, especially between 45-and 65-m depths and between 170-and 185-m depths in Lake Nyos (Fig.…”

Section: Resultssupporting

confidence: 62%

“…This recharge led to a maximum CO 2 content of 1.50 Ϯ 0.06 ϫ 10 10 mol in 2001 at Lake Nyos and 6.28 Ϯ 0.01 ϫ 10 8 mol in 2003 at Lake Monoun, the last assessments performed before piping ( Table 3). The pipe-degassing operation is described in detail elsewhere (12), and the effects are easily seen in our measurements (Fig. 1).…”

Section: Resultssupporting

confidence: 48%

“…In the model, CO 2 Recharge is initially distributed evenly below 60 m in Monoun and 170 m in Nyos. Gas removal through the pipe is driven by the gas concentration at the inlet, and the CO 2 Pipe term was estimated by using the measured relationship between the current, maximum pipe flow rates in both lakes (12), and the gas pressures at the pipe inlets ( Fig. 1 A and B).…”

Section: Methodsmentioning

confidence: 99%

“…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)(10)(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 mitigation, and it was unclear whether the degassing operation undertaken to prevent these disasters could instead disrupt the physical stability of the lakes and trigger another gas burst (13,14).…”

mentioning

confidence: 99%

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Degassing Lakes Nyos and Monoun: Defusing certain disaster

Kling

Evans

Tanyileke

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

106

108

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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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Section: Resultssupporting

confidence: 62%

Section: Resultssupporting

confidence: 48%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Degassing Lakes Nyos and Monoun: Defusing certain disaster

Kling

Evans

Tanyileke

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

106

108

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“…Some meromictic lakes became famous through their dangerous gas loads (e.g. Lake Nyos and Lake Monoun in Cameroon, Halbwachs et al, 2004). The monimolimnion of Lake Kivu contains considerable methane deposits (Tietze, 1978), which are likely to be exploited in near future.…”

Section: Introductionmentioning

confidence: 99%

Quantitative analysis of biogeochemically controlled density stratification in an iron-meromictic lake

Nixdorf

Boehrer

2015

Hydrol. Earth Syst. Sci.

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Abstract. Lake stratification controls the cycling of dissolved matter within the water body. This is of particular interest in the case of meromictic lakes, where permanent density stratification of the deep water limits vertical transport, and a chemically different (reducing) milieu can be established. As a consequence, the geochemical setting and the mixing regime of a lake can stabilize each other mutually. We attempt a quantitative approach to the contribution of chemical reactions sustaining the density stratification. As an example, we chose the prominent case of iron meromixis in Waldsee near Doebern, a small lake that originated from near-surface underground mining of lignite. From a data set covering 4 years of monthly measured electrical conductivity profiles, we calculated summed conductivity as a quantitative variable reflecting the amount of electro-active substances in the entire lake. Seasonal variations followed the changing of the chemocline height. Coinciding changes of electrical conductivities in the monimolimnion indicated that a considerable share of substances, precipitated by the advancing oxygenated epilimnion, re-dissolved in the remaining anoxic deep waters and contributed considerably to the density stratification. In addition, we designed a lab experiment, in which we removed iron compounds and organic material from monimolimnetic waters by introducing air bubbles. Precipitates could be identified by visual inspection. Eventually, the remaining solutes in the aerated water layer looked similar to mixolimnetic Waldsee water. Due to its reduced concentration of solutes, this water became less dense and remained floating on nearly unchanged monimolimnetic water. In conclusion, iron meromixis as seen in Waldsee did not require two different sources of incoming waters, but the inflow of iron-rich deep groundwater and the aeration through the lake surface were fully sufficient for the formation of iron meromixis.

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Boehrer

Schultze

2004

Handbuch Angewandte Limnologie: Grundlagen - Gewässerbelastung - Restaurierung - Aquatische Ökotoxikologie - Bewertung - Gewäss

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Degassing the “Killer Lakes” Nyos and Monoun, Cameroon

Cited by 79 publications

References 9 publications

Degassing Lakes Nyos and Monoun: Defusing certain disaster

Degassing Lakes Nyos and Monoun: Defusing certain disaster

Quantitative analysis of biogeochemically controlled density stratification in an iron-meromictic lake

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