Lake Nyos reported red and rumbling.

Lake Nyos reported red and rumbling

The U.S. Agency for International Development(AID) officially released its final report Feb. 11 on the Lake Nyos disaster that killed at least 1,700 people last August when a gas cloud escaped from the Cameroon lake (SN: 1/17/87, p.36). The agency also made public "Lake Nyos Revisited,' a preliminary report by two scientists sent to Cameroon by AID after a French and a Cameroonian geologist reported hearing rumbling and the sound of waves on the lake Dec. 30.

According to this preliminary report,written by Haraldur Sigurdsson at the University of Rhode Island in Kingston and William Evans from the U.S. Geological Survey in Menlo Park, Calif., the French and Cameroonian geologists also said they heard noises accompanied by flashes of light from the direction of nearby Lake Njupi. The report notes that at times in December both lakes were red.

During their visit to Lake Nyos Jan.20-25, Sigurdsson and Evans conducted interviews, made temperature profiles, collected gas and water samples and did a bathymetric survey of the lake. They also visited Lake Njupi. Like the final AID report on the August event, "Lake Nyos Revisited' concludes that there is "no evidence of recent volcanic activity in the lake.' Instead Sigurdsson, Evans and the other AID researchers who have visited the lake believe the August event was caused by a disruption of the layering of the lake, allowing carbon dioxide, which had been building up in the highly stratified lake, to escape.

Sigurdsson and Evans write that duringtheir January visit they observed rockfalls from the cliffs surrounding the lake, and also noted scars on the cliffs from rockfalls or earlier landslides. They suggest that such a rockfall may have triggered the release of the August cloud. A rockfall might also have been the source of the noises heard by the geologists in December. If so, write Sigurdsson and Evans, it may have brought a little of the oxygen-deprived deep water to the surface. Iron in the rising deep water would then have been oxidized at the surface, giving the lake a reddish cast.

Both reports warn that Lake Nyos andother Cameroon lakes may still be hazardous. They recommend that anthropological studies be conducted to determine how unusual cloud emissions have been in the region. They also suggest that pipes be installed in Lake Nyos to siphon off the carbon dioxide that builds up at the bottom. According to an AID official, the international science teams sent to study Lake Nyos will meet in Cameroon March 16 to compare results.