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Current status of the debate about the age of Lake Nyos dam (Cameroon) and its bearing on potential flood hazards

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Abstract

Scientific visits to Lake Nyos in Northwestern Cameroon in the aftermath of the gas disaster that killed over 1,750 people in 1986 revealed the presence of a pyroclastic natural dam in the northern border of the lake. This dam is being affected by back erosion. Collapse of the dam could cause a flood that would affect inhabited areas over a 220 km distance. Timing of dam collapse has been hotly debated based on vastly different carbon-14 and potassium-argon formation ages. In previous work, we used uranium series disequilibria to suggest a formation age of >5,000 years. Detailed comparison of uranium series and trace element data for lavas of Lake Nyos and Mt. Cameroon, both belonging to the Cameroon Volcanic Line, suggests that Lake Nyos basalts erupted with an initial radium-226/thorium-230 ratio that is two times higher than lavas erupting on Mt. Cameroon today. This information is used to infer an age of 8,750 ± 490 years, which we suggest is the formation age of the Lake Nyos dam. The erosion rate deduced from this age does not indicate that collapse of the dam from back erosion alone and the attendant potential flood disaster are as eminent and alarming as previously thought. However, other factors militate for action to secure the dam. Work is underway to reinforce it by engineering methods.

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Acknowledgments

Samples were collected from Lake Nyos using funds from the 2003 Monbusho International Scientific Research Program (#16403012) to Emeritus Professor Minoru Kusakabe (standing in a pothole on Fig. 1c). Analyses were done at the Okayama University Institute for Study of the Earth’s Interior (ISEI) in Japan when AFT was on a ‘mis à la disposition’ of ISEI from the Cameroon Ministry of Scientific Research and Innovation (MINRESI). Work at ISEI was supported by COE-21 research grants to Prof. Eizo Nakamura and also by JSPS grants for ‘Asia–Africa Science Platform Program’ (AASPP - Geochemistry of Lake Nyos gas disaster, Cameroon Volcanic Line-Rift Valley volcanoes and the underlying mantle). Collaboration from colleagues and administration of ISEI is acknowledged. Pictures shown in this article were taken during many trips to Lake Nyos within the framework of (1) the Lakes Nyos and Monoun Degassing Project funded by the Government of Cameroon, USAID and the French Cooperation; (2) SATREPS-IRGM project headed by Prof. Takeshi Ohba of Tokai University (Japan) and funded by the Government of Cameroon, the Japan International Cooperation Agency (JICA) and the Japan Science and Technology Agency (JST); (3) the Lake Nyos dam reinforcement project funded by the Government of Cameroon & the European Union. We acknowledge the leadership of MINRESI, through IRGM (Drs. Joseph Hell, Luc Sigha and Greg Tanyileke) that coordinates all these projects. Review comments from Prof. J. P. Lockwood and an anonymous reviewer are thankfully acknowledged.

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Authors and Affiliations

  1. Institute for Geological and Mining Research (IRGM), P.O Box 4110, Yaoundé, Cameroon

    Festus Tongwa Aka

  2. Division of Scientific Policy and Planning (DPSP), Ministry of Scientific Research and Innovation (MINRESI), P.O. Box 1457, Yaoundé, Cameroon

    Festus Tongwa Aka

  3. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan

    Tetsuya Yokoyama

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  1. Festus Tongwa Aka
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  2. Tetsuya Yokoyama
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Correspondence to Festus Tongwa Aka.

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Aka, F.T., Yokoyama, T. Current status of the debate about the age of Lake Nyos dam (Cameroon) and its bearing on potential flood hazards. Nat Hazards 65, 875–885 (2013). https://doi.org/10.1007/s11069-012-0401-4

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