Carbon dioxide is one of the most well-known gases. It is produced in respiration a process which produces energy in living organisms. It is also in burning process. Contrarily, it is consumed in photosynthesis a process by which plants prepare their food. These opposite processes keep a constant concentration(i-e 0.03% by volume) of carbon dioxide in air. This carbon dioxide in air keeps the earth warm by absorbing infra-red radiation and emitting it back to the earth a phenomenon known as Green House Effect. When carbon dioxide is present in normal concentrations, this effect is helpful to maintain the normal average temperature of the earth. Higher concentrations of carbon dioxide however, result in an increase in Earth’s average temperature called Global Warming.
Presence of carbon dioxide in atmosphere makes natural rain slightly acidic. This is because, when dissolved in water it forms an acid called Carbonic Acid. This carbonic acid helps in another natural process called Weathering of rocks. In this process rocks are disintegrated to form soil. Carbon dioxide is a toxic gas. Therefore Nature has managed to remove it from our bodies through exhaling. However, if someone is caught in carbon dioxide cloud, death is certain. This is what happened in Cameroon on 21st August 1986.
Although a similar incident had occurred at a neighboring lake. Lake Monoun two years ago, nobody suspected Nyos to be a killer Lake too. Carbon dioxide released from Lake Monoun had killed 37 people in 1984. However due to large size of Lake Nyos, the volume of gas evolved was much larger affecting an area of 25 km from the lake and asphyxiating 1700-1800 people and thousand of cattle and wild animals.
Lake Nyos is a creator lake formed as a result of volcanic about eruption about 400-500 years ago. Although the volcano is extinct, magma present below Lake Nyos release carbon dioxide into its water. Carbon dioxide can be dissolved in water by applying pressure. By reducing pressure or increasing temperature, it can be removed from solution. All of us have experienced it. Opening a Pepsi(or any carbonated drink) bottle, we actually reduce pressure from the solution of carbon dioxide in water and can see its ascending bubbles.
Lake Nyos is a deep lake. Pressure at its bottom is sufficient to dissolve carbon dioxide in water. Low temperature at bottom is another supporting factor for keeping carbon dioxide in solution. Water containing dissolved carbon dioxide is heavier as compared to pure water. Hence it does not mix with upper layers of water. In other words we can say that different layers of water are present in such lakes depending upon the amount of carbon dioxide dissolved in them.
On saturation, these leke become potentially hazardous because landslides, volcanic eruptions, earthquake or even wind and rain storm can result in the violent release of carbon dioxide. In case of Lake Nyos, scientists suspect that landslides triggered such a release. However the fact carbon dioxide is heavier than air is responsible for the death of so many people and animals. Higher density of carbon dioxide keeps it close to ground, pushing air (and oxygen) upward and asphyxiating people. Millions of cubic meters of carbon dioxide left nothing but death in an area of 25 km from lake. To have an idea of the volume of gas note that one cubic meter contains one thousand liters in it.
