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From The Cover
ENVIRONMENTAL SCIENCES
Degassing Lakes Nyos and Monoun: Defusing certain disaster

George W. Kling ^, , William C. Evans , Greg Tanyileke ^¶, Minoru Kusakabe ^||, Takeshi Ohba , Yutaka Yoshida , and Joseph V. Hell ^¶

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109; U.S. Geological Survey, Menlo Park, CA 94025; ^¶Institute for Geological and Mining Research, Yaounde, Cameroon; ^||Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori-ken 682-0193, Japan; Volcanic Fluid Research Center, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan; and Yoshida Consulting Engineer Office, Morioka 020-0121, Japan

Edited by Stephen R. Carpenter, University of Wisconsin, Madison, WI and approved August 26, 2005 (received for review March 19, 2005)

Since the catastrophic releases of CO₂ in the 1980s, Lakes Nyos and Monoun in Cameroon experienced CO₂ recharge at alarming rates of up to 80 mol/m² 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 12-14%. 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 30% of the gas remaining before the natural gas recharge balances the removal rate. In Nyos the single pipe will remove 25% 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

This paper was submitted directly (Track II) to the PNAS office.

To whom correspondence should be addressed. E-mail: gwk{at}umich.edu.

© 2005 by The National Academy of Sciences of the USA

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