HILO, Hawaii — Teams of scientists from five different countries who have studied the area in West Africa where at least 1,700 people died mysteriously last August have concluded that the victims were killed by carbon dioxide of volcanic origin. And they warned that the tragedy could be repeated elsewhere without warning.
Although the scientists disagree among themselves over how the gas was released, they are in agreement that the gas was "magmatic," meaning it came from the same kind of molten subsurface reservoir that fuels volcanoes around the world.
The cloud of deadly gas erupted from Lake Nios in Cameroon and swept through the village of Nios, killing people so swiftly that their bodies were found in the same positions they had been in before the eruption--sleeping, eating, or sitting in the quiet African night.
Seminar on Volcanoes
The scientists, from the United States, France, Great Britain, Italy and Japan, presented their findings late Friday night during an international seminar on volcanoes here.
Most of the scientists arrived in Cameroon within a few days of the deadly eruption, and throughout their investigation they worried about the lake suddenly releasing another cloud of gas.
No significant amounts of gas were released while the scientists were on the scene, but on Dec. 30, according to local witnesses, the lake erupted three more times over a period of a few minutes. The witnesses were on a hillside high above the lake, and thus spared the devastation that swept silently through Nios last August.
The findings confirmed earlier speculation that the victims died from carbon dioxide poisoning, but the scientists warned that Lake Nios could erupt again at any moment, and other volcanic areas around the world could face similar tragedies.
What appears to makes the findings conclusive is the fact that all five teams were working independently, but they reached the same conclusion on what killed the people of Nios.
"Each of us was at Cameroon at different times with different equipment," said Jack Lockwood of the U.S. Geological Survey.
That could explain why the teams reached different conclusions on how the gas was released. Some believe that there was a violent eruption of a volcanic nature. Others think that gas slowly seeped into the lake until it reached saturation, setting off a reaction that sent a giant plume of gas into the air in a process that is somewhat like popping the cork on a bottle of champagne.
Whatever the cause of the release, all agree that the events sent a cloud of odorless, colorless carbon dioxide wafting up the valley toward the village of Nios. Nearly every living creature in its path was suffocated by the gas, which deprived the victims of oxygen when it was inhaled. The gas left at least 300 head of cattle lying lifeless on the grassy slopes of the lake.
'Only Four Survived'
"There were 1,200 people in the village," said Michele Tuttle of the U.S. Geological Survey. "Only four survived." The village is a little more than two miles from the lake.
Others were killed in nearby areas, and the total number of deaths has been set at 1,700, she said.
"But that is probably a conservative estimate," she added. "Some have estimated the total may have gone as high as 3,000." The exact number is uncertain because many bodies were buried quickly to reduce the chances of disease spreading throughout the area.
"We were surprised to see no destruction due to an explosion," said Francois Le Guern, a member of the French team who was one of the first scientists to arrive on the scene. He said a large volume of water had been blown out of the lake by whatever caused the gas release, but the homes appeared to be untouched.
Evidence of Peril
Every place he looked, Le Guern saw evidence of the peril he and his fellow scientists were facing in studying the area.
"We were surprised to find gas escaping from all around the lake," he said. "We were afraid of a new event."
Le Guern used a small rubber raft to explore the lake, taking water samples from deep below the surface and analyzing the gas. Several times the lake turned red in color, just as it had during the eruption, apparently from elements released from the magma far below the lake bottom.
He used empty whiskey bottles donated by a nearby French army post to collect the samples, but the water was so rich in gas that some of the bottles exploded when the gas expanded as the bottles were pulled toward the surface, he said.
Nearly all the gas was carbon dioxide with only traces of methane and helium, further evidence of magmatic origin, he said.
Convinced of Explosion
The French team is convinced that the gas was released in an explosion, based partly on an eyewitness who was high on a hill and is believed to be credible. The witness said he saw a flash of light and heard an explosion. That would explain why 200,000 tons of water was flushed out of the lake.
However, the English scientists believe that there was a gradual buildup of carbon dioxide that was released suddenly when the lake could absorb no more. That conclusion is based partly on the fact that there was no evidence of a major disturbance on the bottom of the lake.
Sam Frieph, a geophysicist on the English team, said the erupting gas would have carried water with it, thus explaining the sudden depletion in the level of water in the lake.
The scientists, who showed dramatic films of their investigation, expressed repeated concerns that the tragedy of Nios could be repeated elsewhere. Le Guern noted that Mt. Vesuvius near Naples has vents that release small amounts of carbon dioxide.
"Is it possible such a thing could happen at Naples?" he asked.