The Dam Hiding a Second Disaster

Name: The Dam Hiding a Second Disaster
Genre: Documentary

Even after the gas catastrophe, researchers discover that the structure holding Lake Nyos above the valleys is itself a hazard.

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Transcript

Dam collapse would threaten about 10,000 people living in valleys below the lake.
On August 21st, 1986, accumulated carbon dioxide escaped from the water.
This was a limnic eruption: carbon dioxide released as a cloud from water.
It killed about 1,700 people and 3,500 domestic animals.
The USGS final report was published in 1987 as Open-File Report 87-97.
Carbon dioxide accumulated in Lake Nyos; the dam is made of pyroclastic surge deposits.
Pipes anchored to a raft remove gas from the lake.
The loose deposits leave the natural dam vulnerable to erosion.
The Nyos maar eruption produced pyroclastic surge deposits.
One study dated that eruption to about 12,300 years ago.
Beneath the lake and nearby ground, the basement rock is mostly granite.
Nearby pyroclastic rocks hold broken basement granite and peridotite xenoliths.
A collapse could send a destructive flood through the valleys below.
A calm shoreline can hide danger in both water and stone.
Carbon dioxide built up in deep water, trapped beneath heavier layers.
The natural dam is porous, with erosion channels cutting through its narrow crest.
After 1986, engineers installed a system to degas Lake Nyos.
Engineers monitor the system as water rises through the pipe, releasing gas.
The degassing fountain could reach about 150 feet (45 meters) above the lake surface.

To drain the gas without triggering the lake, engineers would have to turn Lake Nyos into its own pump.

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