Underwater landslide can cause lake gasses to come to the surface
Sudden underwater landslides or other geologic activity have the potential to churn the lake enough to send both gases bubbling to the surface. Since carbon dioxide is heavier than air, it would hug the ground, asphyxiating all humans and animals that it reached. Such a disaster occurred in 1986 at Lake Nyos in Cameroon, West Africa, where 1,700 people were suffocated, many quietly as they slept. Lake Kivu contains 350 times as much gas as Nyos and has far more people living near its shoreline.