Orders on Thursday to evacuate Goma, a city lying in the shadow of DR Congo’s Mount Nyiragongo volcano, have shed light on a rare but potentially catastrophic risk — a “limnic eruption,” when volcanic activity combined with a deep lake can spew out lethal, suffocating gas.
The phenomenon first came to the world’s attention in August 1984, when 37 people mysteriously died at Lake Monoun in western Cameroon.
Scientists found that dissolved carbon dioxide (CO2) gas in the depths of the lake had erupted, creating invisible clouds at the surface that were borne by winds into homes and fields, snuffing out life.
Two years later, more than 1,700 people and thousands of cattle died in Lake Nyos, also in Cameroon, strengthening the belief that earthquakes and volcanic activity can trigger these unusual events.
More than 600,000 people live in Goma, although the region’s population is around two million, in addition to more than 90,000 people who live across the border in the Rwandan city of Gisenyi.
Both cities lie on the northeastern shore of Lake Kivu, which is dominated by Nyiragongo, a strato-volcano nearly 3,500 metres (11,500 feet) high that straddles the East African Rift tectonic divide.
The much-feared volcano roared back into life on Saturday, spewing two rivers of lava over the next day that have claimed 32 lives and left around 20,000 homeless.
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