On the night that it would kill, Lake Nyos looked as peaceful as always, its deep blue water silent and calm and bumping softly against the rocky shores of northwest Cameroon. The lake, sitting high on the flank of an inactive volcano within the Oku Volcanic Field, was surrounded by small rural villages and farms, far from a city of any consideration.
At 9pm, the quiet was broken by a low rumbling that could be heard from the homes nearby. Anyone who looked at the lake could see the now deep red water and the faint white mist rising from it. The mist looked like nothing, like rain or fog, but it carried with it a death sentence. It spilled over the northern tip of the lake, then quickly rushed into the surrounding valleys. Within minutes, it had taken the lives of some 1,700 people within 16 miles of the lake as well as 3,500 livestock. About 4,000 inhabitants fled the area, but many of these developed respiratory problems, lesions, and paralysis as a result of the gases.
The white mist was carbon dioxide. It had been released from the lake in such volume, somewhere between 100,000 – 300,000 tons, that it displaced the oxygen in the air and suffocated most of those it came in contact with.
One survivor, Joseph Nkwain from Subum, described himself when he awoke after the gases had struck:
“I could not speak. I became unconscious. I could not open my mouth because then I smelled something terrible . . . I heard my daughter snoring in a terrible way, very abnormal . . . When crossing to my daughter’s bed . . . I collapsed and fell. I was there till nine o’clock in the (Friday) morning . . . until a friend of mine came and knocked at my door . . . I was surprised to see that my trousers were red, had some stains like honey. I saw some . . . starchy mess on my body. My arms had some wounds . . . I didn’t really know how I got these wounds . . .I opened the door . . . I wanted to speak, my breath would not come out . . . My daughter was already dead . . . I went into my daughter’s bed, thinking that she was still sleeping. I slept till it was 4:30 p.m. in the afternoon . . . on Friday. (Then) I managed to go over to my neighbors’ houses. They were all dead . . . I decided to leave . . . . (because) most of my family was in Wum . . . I got my motorcycle . . . A friend whose father had died left with me (for) Wum . . . As I rode . . . through Nyos I didn’t see any sign of any living thing . . . (When I got to Wum), I was unable to walk, even to talk . . . my body was completely weak.”
Most were killed in their sleep. In some cases still-awake relatives didn’t even immediately realize it, as they remained unaffected due to the dense gas settling low to the ground and reducing in concentration higher up. Some villagers came out of their houses after hearing sounds and were overtaken by wafting clouds of gas, falling dead at their doorsteps. In Nyos village only six out of 800 survived by getting to higher ground. Those that did watched every flame and fire below them extinguish as the CO2 settled, snuffing out life.
Where had the deadly gas cloud that had wiped out so many come from? It was soon discovered that Lake Nyos is always saturated with carbon dioxide due to a pocket of magma which lies beneath it. Typically, the less dense water near the surface floats on the colder, denser water layers near the lake’s bottom, which is where the carbon dioxide gas seeping into the cold water is dissolved. In this state, the lake is stable. But on the night of August 21, 1986, something triggered the release of that gas. The cause still remains unknown, and theories range from a landslide, a small volcanic eruption, or even cool rainwater falling on one side of the lake and triggering the overturn.
To prevent the tragedy from reoccurring, 3 pipes were installed in the lake that lift the heavily saturated water from the bottom of the lake until the loss of pressure begins releasing the gas from the diphasic fluid, making the process self-powered. This has relieved the concentration, but the lake could be a ticking time-bomb, waiting for the next triggering event. Even more disconcerting, investigation of other African lakes found that Lake Kivu in Democratic Republic of Congo, 2,000 times larger than Lake Nyos, was also found to be supersaturated. A project is in progress to systematically extract carbon dioxide, hydrogen sulphide, and methane from the lake. It addition to preventing any future disasters, the gasses will be used for energy generation.
While these lakes still pose a danger to those that live near them, there is hope that these measures prevent any future catastrophes. Despite the risks, the area is being resettled. Some come to take advantage of the great fertility of the area, but most simply wish to make a return to their ancestral lands.