Both lakes occupy the crater of a supposedly extinct volcano, in a region known by geologists for its numerous gaseous water springs, a common feature of old volcanic areas. The region belongs to the so-called volcanic chain of Cameroon, which ends and culminates 300 km farther south-west at the still active Mt. Cameroon (4,000 m ).
The lake Nyos disaster, which claimed 1800 victims in August 1986, was not unprecedented, but never before one had heard of Mother Nature asphyxiating human beings and all terrestrial animals on such a scale in a single and brief event.
Two years previously however, a lethal gas burst originated from the neighbouring lake Monoun, in the same remote area of Cameroon, and killed 37 people, an odd and tragic episode that went almost unnoticed.
In both cases, without prior notice, a cloud of dense gas erupted from the lake, covering the surrounding area under a deadly blanket several tens of meters thick, for an unknown amount of time. The source of the gas became clear in the aftermath of the disasters, since the normally clear waters of the lakes turned reddish and the lake shores were severely disturbed by waves and strong winds. No one in the path of the cloud managed to escape its lethal effects. Skin discoloration found on some victims were tentatively interpreted as burns, but this diagnosis is still controversial. Witnesses on topographic hights report a loud noise originating from the lake and, in the case of lake Nyos, flashes of light visible over the lake ; both disasters occurred at night, darkness adding to the mystery of these dreadful natural catastrophes.
Ten years later, thanks to the dedication of scientists - such as H. Sigurdsson, K. Tietze, G. Kling, W. Evans, M. Kusakabe and G. Tanyileke, to name but a few - who put both lakes under almost continuous scrutiny, the causes and mechanism of these tragedies are much better understood, albeit not yet completely elucidated.