When most of us hear the word eruption, we almost instinctively associate such images as smoking mountain tops and cascades of hot bubbling lava. However, there is another type of natural disaster in our midst that has somehow slipped public consciousness, which isn’t surprising since there have only been two documented cases throughout history.
A Limnic Eruption is a very rare disaster in which a toxic amount of carbon dioxide (CO2) is abruptly released from within the confines of a body of water like a lake. The result of this gas expulsion, also commonly referred as a “lake overturn”, can cause an almost instantaneous form of asphyxiation, suffocating wildlife and humans alike. Another theory also suggests that a limnic eruption may also possess the ability to displace a body of water enough to trigger a tsunami.
-What Can Cause a Limnic Eruption-
To answer this we must consider the only two historically documented events, which curiously both took place within the Republic state Cameroon, situated in central Africa.
After thorough investigation of these two events, scientists and geologists have determined that volcanic activity may be the actual source of the two disasters. Basically, in order for an eruption to occur the lake must be thoroughly saturated with gas. In both recorded events the majority of the gas was carbon dioxide, which they believe may have been released through a volcanic fissure under the lakebed. Another theory that has been considered is that the gas came from an extended period of decomposition of organic material, which overtime slowly seeped into the waters of the lake.
Now, the eruption part only takes place when the lake reaches a saturation point at which time the lake unwittingly becomes a ticking time bomb. An interesting example of this limnic behavior can also be found in a can of soda, which similar to a suspected limically active lake, contains pressurized liquid saturated with carbon dioxide. To demonstrate lets consider the following: If you were to put your ear to a can of unopened pop, what would you hear? Nothing, right, which is because the carbon dioxide is still being contained by the pressure within the confines of the can! Now, if you crack the tab, releasing the pressure, a quick rush of air will be heard, followed by that familiar fizzing sound, which is actually bubbling carbon dioxide.
A limnically active lake is basically similar to a can of unopened soda pop, which once enough carbon dioxide has dissolved the lake reaches a highly unstable saturation point. Now, all it needs is someone to crack the tab, or in this case trigger the carbon dioxide release. In both cases in Africa the catalyst was determined to be unknown, although evidence collected support strong indications that landslide spill over and temperature played into both events. This brings us to another important factor; pressure, which unlike mechanical processing, lakes require extreme depth to produce the necessary pressure to distribute enough carbon dioxide to produce a limnic eruption.
The first recorded event took place on August 15, 1984 at Lake Monoun in the province of Cameroon, Africa. The event expelled well over 80 enough toxic gas that it killed as many as 37 people living within proximity of the lakebed. Reports also indicate all life forms contained in the lake and around the lake were also killed by asphyxiation.
The second ever-recorded event took place nearly two-years later, on the evening of August 21, 1986, which oddly enough also took place in the same province of Cameroon, striking Lake Nyos, a crater lake just less than 70 miles north-west of Lake Monoun. Unfortunately, Lake Nyos had a much denser population, and this time 1700 people and over 3500 livestock died of asphyxiation, which later was catalogued as the first-known mass scale natural occurring case of asphyxiation.
The Lake Nyos event later was determined to be related to the fact that the lake was formed from the collapse of the pipe (entrance) feeding into a now extinct or non-active volcano. This also could mean that underlying pockets of magma are still releasing carbon dioxide into the waters of the lake.
-Limnic Prevention Methods-
Ultimately there are several conditions that can trigger an eruption. Excessive rain, landslides, seismic disturbances, and even temperature flux, are all indicative catalysts. So, the only hope now is to diffuse the bomb, or in this case; safely release the gas. In 1995 a group international based scientists and geologists, implemented a solution to vent the gas from a limnic lake. The process involved using a strong polyethylene pipe, which was placed vertically to the lake bottom. Basically, since most of the carbon rich water lies at the bottom, the deeper water is pumped to the surface, and as the deep water rises up through the pipe the carbon dioxide is dispelled.
Interestingly due to natural forces, the gas and water become buoyant, which self propels more water in at the bottom, thus creating a self-sustaining process. Degassing though may propose a problem, since there is always a fear that too much degassing will cause an actual limnic eruption. The Lake Nyos project particularly poses another problem, due to the volcanic rock forming a natural dam may be weakened, which if the dam failed or was breached, the spilling of the water would trigger an immediate limnic eruption, which would also flood as far as Nigeria.
Nature is full of wonder and beauty, but at the same time it also has a sizable number of perils. Limnic eruptions are but one of many events that could threaten thousand or possibly millions of lives. Limnic lakes are essentially rare, and are only common in tropical or warmer climates like Africa. Luckily, scientists have been very successful so far with efforts to lower the carbon dioxide levels in both Lake Nyos and Monoun, which may prevent another tragedy like a limnic eruption.