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The Killer Lakes of Cameroon

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The Killer Lakes of Cameroon Lakes in the news: The Killer Lakes of Cameroon Scientific Team: Bill Evans Action needed on Michel Halbwachs NATURE published online: deadly lakes Who’s Involved? George Kling 26 September 2005; | By Richard Black doi:10.1038/news050926-4 Environment Correspondent, BBC News Who’s Affected? Minoru Kusakabe website What happened? Jack Lockwood Deadly lakes may Tuesday, 27 September 2005, 11:37 GMT 12:37 More work is needed urgently Greg Tanyileke explode again to prevent potentially fatal Michele Tuttle Pipes to avert disaster are releases of gas from two lakes Yoshida Yutaka working, but not quickly in Cameroon, scientists say. enough. Others involved: Andreas von Bubnoff - U.S. Embassy, Cameroon - U.S. Office of Foreign Cameroon Dam Nears Collapse, Disaster Assistance 10,000 Lives at Risk (OFDA-USAID) August 19, 2005 — By Tansa Musa, Reuters - U.S. Geological Survey YAOUNDE — A natural dam holding back a lake in Cameroon is on the verge of collapse, threatening to unleash a wall of water into neighbouring - U.S. EPA Nigeria and sweep away 10,000 people in its path, a scientist warned on Thursday. - U.S. Defense Mapping Agency (DOD-NGA) National Geographic, Smithsonian - Cameroonian Government Discovery Channel, Discover Magazine The Learning Channel, PBS - Japanese Government BBC Film & Broadcasts, World Book - French Government Scientific American, Voice of America Who’s Affected? Introduction and Background Lake Monoun Region: ~3,000 people living or working near the lake. Only 3 lakes in the world are known to have high concentrations of gas: NIGERIA Lake Nyos Region: Lakes Nyos and ~5-10,000 people in the floodplain below the Monoun in Cameroon, lake, including people living in Nigeria. and Lake Kivu in East Africa. Lake Nyos in May 1985 before the disaster Lake Nyos ~10 days after the disaster in August 1986 1 Why does the gas stay in the lake? After the gas burst Lake Nyos had similar temperatures from Surface Waters top to bottom, (less dense) indicating that mixing occurred during the gas release. The surface water Bottom Waters warming was due to (more dense) the sun. Note also that the CO2 and salts increase water oxygen was gone by density 10m depth. A typical lake is “stratified”, i.e., has layers of different density. 3 Aerial view of Lake Nyos – up to 1 km of CO2 was released Lakes higher in elevation have colder bottom waters. The gas-water fountain produced by the explosion reached over 100 m (300 feet) in height (and went over the rock promontory shown at left), and produced a surface wave 30 m (100 feet) high. The gas cloud killed people up to 26 km (16 miles) away from the lake. 2 SOURCE: Most volcanoes produce large 1. Volcanic (hot) amounts of toxic sulfur 2. Biogenic gases, and heat. 3. Magmatic (cool)* Survivors reported STORAGE: smelling rotten eggs or gunpowder, and 1. Fissures below the sediment feeling warm. 2. Bottom waters of the lake* Spring CO charged Formation of Lake bottom water 2 is chemically similar soda spring in CO -charged 2 to nearby springs Cameroon soda springs Groundwater Gas from magma contacts groundwater CO2 from magma Lockwood and Rubin, 1989 High crater rims shelter the lakes from the Lake bottom water mixing effects of the wind is chemically similar to nearby springs 3 Deep lakes have more resistance to mixing Mixing is greatest during the late summer monsoon season. Climate near The climate near Barombi Mbo Lake Nyos is also since 1968 is consistent with consistent with deepest mixing in deepest mixing in August. August, the time of the events. 4 Rainfall was high in 1986, but not in 1971 Temperature was low in 1986, but, also in 1971 Nyos looked calm and normal 1 year after the disaster How does the gas get out of the lake? Any movement of deeper water toward the surface could trigger a gas release if the lake is saturated – just like opening a bottle of soda or champagne. Most likely, a landslide into the lake triggered the gas burst – this danger still exists gas gas landslide gas Deep-water temperatures continued to rise Gas Pressures continued to rise in the lakes 5 Failure of the weak natural dam at Lake Nyos will create a flood that would reach into Nigeria, 100s of km away. The natural dam is eroding rapidly, and already leaking Remediation for Lake Nyos Hazards Lake Nyos-Monoun Degassing Gas Bursts and Flooding Program, NMDP 1. Pump Bottom Water International Project – Cameroon, France, Japan, U.S.A. 2. Reduce Gas Content Directed by an Inter-Ministerial Committee in Cameroon Supported by OFDA/AID and foreign governments 3. Reduce Danger of Gas Burst Project includes: 1. Lake monitoring – ongoing since 1986 4. Lake Level Held Constant 6. Lake Level Lowered 2. CO2 warning stations – installed at both lakes in 2001 3. Construction of roads and buildings at both lakes 5. Flood Danger Remains 7. Flood Danger Reduced 4. Degassing system – rafts, pipe, and instrumentation Delay flood mitigation * Pipe installation at Lake Nyos in January 2001 8. Increase Danger of Release until most gas is removed. * Pipe installed in Lake Monoun in January 2003 Dam can be strengthened of Remaining Gas in and or removed Below the Lake CO2 Warning Stations installed at both lakes. The degassing fountain at Lake Nyos is over 50 m (165 feet) high. Once started, the degassing is spontaneous and self-sustaining. Energy could be extracted from the fountain, but there are no power transmission lines in this part of the country. Piping has reduced gas content by 12-14% 6 The degassing fountain at Lake Monoun is over 8 m high. 1. The degassing operation has reduced the gas content in the lakes. L. Nyos Gas Pressure 40 1992 60 1998 2001 2003 Post-Degassing 80 Hydrostatic 100 120 140 Depth (m) Depth 160 inlet 180 200 2 4 6 8 10 12 14 16 The degassing fountain at Lake Total in situ Gas Pressure (bar) Monoun is ~33 feet (10 m) high. L. Monoun Gas Pressure 2. The degassing operation has not disrupted the layering in the lake – i.e., the degassing is proceeding 1992 in a controlled and safe way. 20 1998 2003 Lake Nyos Conductivity (μS/cm) Hydrostatic2004 Post-Degas 0 Hydrostatic C. Nyos 40 -20 -40 -60 2400 60 -80 2000 Degassing Begins Depth (m) Depth -100 1600 80 -120 1200 Depth (m) -140 800 -160 400 100 -180 0 12345678 -200 Total in situ Gas Pressure (bar) 1995 1997 1999 2001 2003 Year From PNAS (2005) 102:14185-14190 MODELING OF FUTURE STATUS IN THE LAKES: 1.4 5 pipes The Future of Degassing 1.2 1 pipe A. Nyos [CO2_Total] = [CO2_Initial] mol) 1.0 In a relatively short time the + [CO2_Natural Recharge] 10 current degassing operation 0.8 – [CO2_Pipe Removal] with one pipe in each lake will 0.6 – [CO2_Diffusion + Ventilation to atmosphere] become ineffective. (x10 0.4 min released 2 0.2 Modeling results indicate that Ventilation to atmosphere Pipe Removal CO more pipes added to each lake will increase the amount of gas 2000 2005 2010 2015 removed, and decrease the time that local populations will be in 6 B. Monoun 2 pipes danger. Low CO2 1 pipe 5 mol) Diffusion 8 4 High CO2 3 10 (x 2 2 The dashed lines indicate the amount of gas CO 1 Natural Pipe remaining at atmospheric pressure (0.9 bar), and inlet 2004 2006 2008 2010 the “min released” shows the amount of gas Recharge released in the 1986 disaster at Lake Nyos. Year From PNAS (2005) 102:14185-14190 7 Politics of Scientific Debate (Related to Natural Hazards, or Climate Change) Take Home Message: Need to overcome the “comfort of inactivity” -- but HOW? Science is only one part of the solution to any problem, but you still 1. Good Science 2. Understand alternate theories have to get the Science right. 3. Logic defeats hand-waving in the end 4. Explain principles to politicians and the solutions will become self-evident (unless they stand to make money from one of the solutions…) 8.
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