Surveying, Mapping and GIS

In examining Rwanda and Cameroon, I came across a number of articles discussing limnic eruptions - this is a natural event, where large amounts of dissolved and trapped gases in lakes suddenly and catastrophically become released, causing death to all living things within a substantial radius of the lake.

Typically this is due to volcanic vents, which release CO₂, which becomes trapped in stratified layers deep in the lake. The trapped gases may remain undisturbed and in solution for long periods of time, and may continue to accumulate until an external event triggers instability, such as earthquake, landslide, rapid thermal change, or the like.

One particularly catastrophic and more well-known instance of this phenomenon is Lake Nyos, in Cameroon, where in August of 1986, an estimated 1,800 people and large amounts of livestock died due to suffocation. It is estimated that 1.6 million metric tons of CO₂ were released in that instance. As CO₂ is heavier than air, the gas fills valleys, and finds its way to low-lying areas in great concentration.

Fortunately this is a relatively uncommon occurrence - few lakes are known to have this type of supersaturation of gases and potential for catastrophic overturn. Lake Nyos is a fairly small lake, of 1.2 km² - Lake Monoun is another small lake in Cameroon which has had similar catastropic incidents and loss of life in the past.

Another lake that is somewhat disconcerting is Lake Kivu, bordering Rwanda and the Democratic Republic of Congo - Lake Kivu is much larger - 2,700 km², with a much larger population along its shores than these other lakes. It is unknown if Kivu is susceptible to similar massive overturn events, and Kivu has considerably greater depth that the two Cameroonian lakes, however it similarly displays the unusual supersaturation of gases characteristic of the other two lakes - and situated over the Rift Zone, and in proximity to Mount Nyiragongo, which last erupted in 2002- it is entirely possible that the same circumstances exist for continued contribution of CO₂ and other gases.

In some instances, the lakes are being degassed, via pipes which seek to gradually release the concentrated gases, similar to slowly letting the fizz out of a soda can.
One such project is being conducted by the Lake Nyos and Monoun Degassing Project.