Cameroon lake: new clues, new clouds?

Cameron lake: New clues, new clouds?

Just as final reports are being issued onthe disaster that killed 1,746 people last August when an asphyxiating carbon dioxide cloud exploded from Lake Nyos in Cameroon (SN: 9/20/86, p.180), the lake may have been racked by three new explosions. On Dec. 30, according to the Associated Press, a French scientist reportedly observed the explosions, accompanied by light flashes, in the space of five minutes. No injuries or fatalities were reported.

However, according to Paul Krumpe atthe U.S. Agency for International Development (AID) n Washington, D.C., that report does not completely jibe with information presented to the U.S. ambassador in Cameroon. "We're not sure exactly what has transpired, if anything," he told SCIENCE NEWS. "We've asked the embassy whether they'd like some technical assistance to evaluate what may or may not have happened."

While scientists who have studied thelake are puzzled by the reports of light flashes, they say the explosions, if confirmed, would be consistent with theories proposed to explain the August event. Studies have shown that the highly stratified lake contains high levels of dissolved carbon dioxide. Many scientists believe that something upset the stratification, causing, a runaway degassing of the lake and the explosive eruption of the carbon dioxide cloud.

The Dec. 30 explosions may be "largerthan what we would have predicted for this soon after the main August event," says volcanologist John Lockwood. But "we're loath to make any statement because we don't know what went on." Lockwood, at the Hawaiian Volcano Observatory on the island of Hawaii, was a member of the team sent to Cameroon by AID.

That team's final report on the Augustevent is scheduled for release this week. Most noteworthy, according to scientists familiar with the report, is the team's resolution of the sulfide mystery: Scientists had speculated that hydrogen sulfide or other sulfur compounds were in the cloud because witnesses reported smelling rotten eggs or gunpowder, both of which have distinctive sulfur odors. Investigators also thought at first that the victims had been burned by sulfuric acid or other chemicals. However, geologists could find no measurable levels of sulfides in the lake.

Members of the medical team say theynow believe the victims' skin lesions, probably similar to bedsores, developed because the people had been lying unconscious for many hours. And, they say, the thermal burns they observed came not from hot gases emitted from the lake, as some had speculated, but because some of the victims had become unconscious next to heat sources such as stoves.

Moreover, the AID researchers foundpast studies in which a large percentage of volunteers subjected to low levels of carbon dioxide had "olfactory hallucinatins" in which they smelled sulfide odors when none were present. The subjects also felt warm, another sensation reported by Cameroon survivors. Happily for the survivors, the AID report notes that no long-term health effects from exposure to the cloud have been found.

As for the geologic analyses, Lockwoodand others says they have added many more data to their initial findings, but have not change the basic conclusions. They believe the lake's carbon dioxide gas has a volcanic origin and had built up slowly in the lake over a long period of time. They still don't know what triggered the explosion, but they don't think a sudden volcanic eruption or an earthquake was responsible.

Without speculating on the cloud'striggering event, two British scientists have arrived at essentially the same conclusion. In the "News and Views" section of the Jan. 8 NATURE, S.J. Freeth of the University College of Swansea and R.L.F. Kay of the British Geological Survey in Wallingford estimate that about 200,000 metric tons of water and about 6,000 metric tons of gas were lost from the lake.

One volcanologist who has held somewhatdifferent views about the cause of the Lake Nyos cloud is Haroun Tazieff, recently retired from the Center for Weak Radioactivity Research in Gif sur Yvette, France. According to Associated Press reports, Tazieff and his colleagues think the cloud was made up of steam, carbon dioxide and sulfur compounds that had been building up in a layer of groundwater heated by volcanic rocks far below the lake. These compounds reportedly were injected into the lake when the pressure of the steam eventually cracked the rock that had been holding it down.

Some U.S. scientists have arguedagainst this theory by noting that lake temperatures were not elevated, its bottom did not appear to have been disturbed, there were no volcanic sulfides in the lake and no suspended sediments that might have resulted had steam rushed through bottom sediments. However, Lockwood says he and other U.S. scientists are reserving judgment because they have not yet seen Tazieff and his colleagues' evidence. Scientists from all the nations involved in studying Lake Nyos may be able to compare their data in February or March at a proposed meeting in Cameroon, according to Krumpe.

The critical question now, says Lockwood,is how dangerous the lake will be in the future. And one key to that hazard assessment is knowing how fast carbon dioxide is being added to the lake. The AID report assumes "that the injection is gradual," he says. "Tazieff would say that there was perhaps a more rapid influx of gas that triggered the event. But no one has evidence that bears on the rate of injection. So what's desperately required are more frequent measurements of the amount of gas dissolved in that lake."