While watching TV recently, I felt thirsty and decided to have a drink. I got a glass and a large unopened plastic bottle of sparkling mineral water, sat down and quickly unscrewed the top from the bottle. You know what happened next - the mineral water boiled up in a frenzy of bubbles and a considerable volume of frothy water gushed into my lap.
On August 26th, 1986, something similar happened in Lake Nyos in Cameroon (an African country lying beside Nigeria). A cloud of lethal gas boiled up from the lake, killing at least 1,700 people and a large number of animals.
At present, conditions in the lake are such that it could explode again at any moment. Cameroon also has another lake, Lake Monoun, that suffers from the same problem -it exploded in 1984, killing 37 people.
The solution to the problem is to install systems to artificially de-gas these lakes. However, these installations have been delayed, largely due to political complexities.
The gas in the case of my mineral water and the Cameroon lakes is carbon dioxide. It is present at the low concentration of about 360 parts per million (0.04 per cent) in our atmosphere. It is not toxic to animals at this level: we inhale it continually and we generate carbon dioxide in almost every cell in our bodies as a by-product of metabolising food to generate energy. We exhale this carbon dioxide into the atmosphere.
Green plants love the carbon dioxide in the atmosphere. They use it in the process of photosynthesis to synthesise carbohydrate and as a by-product they release oxygen into the atmosphere.
There is an overall natural balanced cycle. Animals breathe air in order to extract oxygen which is used to burn food to produce energy, and carbon dioxide is released as a by-product. Plants use carbon dioxide and release oxygen to the atmosphere as a by-product.
Carbon dioxide in air poses no problems for humans at very low levels but it becomes a problem if it rises to high concentrations. Carbon-dioxide concentrations above 10 per cent can be lethal. If you were forced to breathe air containing a high level of carbon dioxide and greatly depleted oxygen you would quickly suffocate. This is what happened at Lake Nyos in 1986.
Nyos is a crater lake, formed by a volcanic eruption that left a plug of magma (hot molten rock) at the crater bottom. When the magma cooled the crater filled up with water to a depth of 210 metres. Many such volcanic lakes are found around the world, but apparently only two have ever exploded, taking human life - Lake Nyos and Lake Monoun.
Carbon dioxide is continuously released deep in the Earth by volcanic de-gassing of magma. The gas rises and dissolves in the groundwater that flows into Lake Nyos. This mineralised gas-rich water accumulates at the bottom of the lake and is overlaid by the upper layers of fresh water.
In most crater lakes the deep water periodically turns over, mixing with the upper fresh water, bringing the carbon dioxide-rich water gradually to the surface where the gas bubbles off harmlessly.
Unfortunately, the lower and upper layers of water in Lake Nyos and Lake Monoun do not turn over. The gas continues to build up in the bottom water until something triggers the deep water to move upwards.
Nobody knows what the triggers are; landslides, earthquakes, strong winds, storms etc are all possibilities. The water at the lake bottom is under pressure and the greater the pressure the greater the concentration of carbon dioxide that stays in solution.
When some bottom water rises to the top, the pressure is greatly reduced and the carbon dioxide bubbles out of solution. This bubbling causes disturbance currents, which pull up more bottom water causing even more bubbling, and so on.
The process quickly gains such momentum that it causes a massive version of my sparkling water incident. Gas-filled water erupts from the lake in a great fountain. The jet was 80 metres high at Lake Nyos, and carbon dioxide filled the air.
Pure carbon dioxide is 50 per cent heavier than air and, when released in volume, will hug the ground, suffocating all animal life it covers. The cloud of cold gas released from Lake Nyos rolled down the hills at 70 k.p.h. filling low-lying areas up to 20 km away.
Lake Nyos is poised to erupt again soon - it now contains twice as much carbon dioxide as was released in the 1986 explosion. This time an explosion might destroy the dam at the northern end of the lake, putting at risk of drowning 10,000 people. Although the area around the lake was evacuated after 1986, many people have returned, drawn by the richness of the land and the good fishing.
The problem could be solved by installing the apparatus to artificially de-gas the lakes at regular intervals. This involves running pipes into the lakes, through which the deep carbon dioxide-laden water froths up to release the gas harmlessly at the surface.
Installing the de-gassing apparatus has been delayed by an amalgam of difficulties. It is a preventive measure, and the aid organisations that must fund the operation tend to be reactive rather than preventive.
Also, the Cameroon government must assist the degassing project in a co-ordinated manner.
Thankfully, it now seems that the de-gassing project is firmly on track. The entire operation should cost about £1 million, very little considering the amount of anguish and misery it will prevent.
William Reville is a senior lecturer in biochemistry and director of microscopy at UCC