Lake Nyos

In African mythology, several Cameroonian tribes believe that the souls of the dead reside below the surface of rivers and lakes waiting for their chance at revenge and to haunt the living for years to come. One such lake is Lake Nyos, known to the locals as "the bad lake." In August of 1986, Lake Nyos claimed the lives of over 1,800 men women and children along with thousands of wild and herded animals in an event that both baffled and scared scientists worldwide. Twenty years since that incident, scientists say that Lake Nyos is as much as a threat to human life as it ever was, and that, "Everyday we wait is just an accumulation of the probability that something bad is going to happen." Scientists need to figure out what caused the deaths, how to fix it and prevent future inevitable disasters.

After the initial report of the catastrophe, it took medical and government officials two days to arrive because of the lake's remote location in the small Cameroonian farming town of Wum. When they did arrive they were shocked by what they found: not only had thousands of cattle died along with countless wild animals, but entire villages had perished overnight as well. There were no clues to go by really. The dead showed no signs of bleeding or physical trauma and no sign of disease and what survivors there were suffered severe burns, respiratory complications, and paralysis. All tests for radiation, poison or chemical usage came up negative. Furthermore there was no sign of suffering or pain, it was as if the entire population just blacked out and died.

Scientists initially had only two clues to go on in determining the cause of the deaths. The first was the distribution of the victims in terms of proximity to the lake. Deaths had been reported as far as fifteen miles from the lake, but the closer they got--the higher the death toll became. In fact when they approached the shore of the lake, they found that even the plant life there was severely damaged if not destroyed completely. They also found that the lake's usually clear blue water had turned a murky, foul colored red. With these disturbing new pieces of information, scientists immediately began speculating what could have caused such a catastrophe.

Lake Nyos, it turns out, is actually what's known as a "crater lake". Crater lakes form when the crater of an inactive volcano fills with water. The scientists initially thought that perhaps the volcano had fired up and released enough gas to kill the villagers and their animals, but no witnesses had reported feeling any earthquakes that would have surely resulted from such an eruption. When they checked a seismic recording station 140 miles away, it showed no evidence of anything unusual. The huts in the nearby villages were not in disarray, their contents sitting neatly on their shelves. They did however, notice one odd thing: the oil lamps in all these homes had been extinguished despite the fact that many of them had plenty of oil in them. With nothing else to go on and the possibility of a volcanic eruption out of the question, scientists looked towards the lake itself and began taking samples of its water. What they found in those samples shocked them, and offered yet another clue to the cause of the deaths.

The scientists began taking samples from various depths within Lake Nyos, which is over a mile wide and six hundred eighty feet deep. They found that that red color on the surface of the water turned out to be dissolved iron, which is normally found not on the top of the lake but the very bottom. Something, they decided, caused a big enough shift to stir up the sediment at the bottom of the lake pushing it to the very top, where the iron then turned to rust when it came into contact with the oxygen at the surface. They also found that the lake contained abnormal amounts of CO2--carbon dioxide. They found that the deeper they took their samples from, the higher the level of carbon dioxide would be. When they reached a depth of six hundred feet, the levels were simply astronomical. They found that at the bottom of the lake there was five gallons of carbon dioxide for every gallon of water! They pieced together a theory that the volcano that formed Lake Nyos still had an active magma chamber below the Earth's crust. While the fact that carbon dioxide was present wasn't anything new (carbon dioxide is present in lakes worldwide), it was the fact that it was never being released and simply collected at the bottom of the lake. Lake Nyos, it turns out, had suffered a limnic eruption.

A limnic eruption is an extremely rare natural disaster, in which carbon dioxide builds up within the lake only to be violently expelled, which in turn poses a threat of suffocation to those around it. It is so rare in fact that there are only two recorded cases of this occurrence--one at Lake Monoun in Cameroon in 1984 which caused the death of 37 villagers, and the Lake Nyos incident. In order for a limnic eruption to occur, a lake must be "flooded" with a gas. In both of the known cases that gas was carbon dioxide. The carbon dioxide can come from one of two known sources: either by gasses given off by an underground volcano, or by the accumulation of decomposed material on the bottom of the lake. When one thinks of "carbon dioxide" and "explosion", they most immediately think of a pop can; this is no exception. When you open a can of soda, the pressure of the CO2 is released, thereby creating the foam and bubbles. With a lake, the bottom is at a much higher pressure than the top. So when the carbon dioxide is pushed to the top, there is no longer enough pressure to contain it and the explosion is the result. Needless to say, with so much CO2 just sitting at the bottom of the lake, it becomes very unstable and not much is needed to trigger an eruption. While a landslide was the suspected trigger in the Lake Nyos case, wind, rainstorms, or even cold snaps are possible triggers. Once CO2 is pushed to the top, bubbles begin to form (indeed, some witnesses to the Lake Nyos explosion reported that the lake seemed to bubble before it erupted), which lifts the water even higher to the lake, where even more CO2 is pulled up to form a column of gas. The water at the bottom of this column is then pulled up by suction, resulting in a runaway eruption of carbon dioxide that could have been accumulating for decades. The eruption also causes a tsunami of the displaced water. Several factors must be present for this to occur. First there has to be a source of CO2, so regions with no volcanic activity would not see this type of eruption. Second, there has to be a lack of convection. Convection is the result of a change of temperature along the surface of the water, whereby the surface water cools causing it to sink lower which in turn brings the carbon dioxide saturated water