Lake Nyos in Cameroon looked like any other tropical crater lake until August 21, 1986, when it burped. Not the cute kind of burp—the kind that killed 1,746 people and 3,500 livestock in a single night.
Nobody heard it coming. No lava flows, no ash clouds, no Hollywood-style pyroclastic drama. Just carbon dioxide, rolling downhill like an invisible avalanche, suffocating everything in its path within a 15-mile radius. The gas was heavier than air, so it settled into valleys where people slept, replacing oxygen with something their lungs couldn’t use. By morning, entire villages were graveyards.
Here’s the thing about volcanic CO2: it doesn’t play by the rules we associate with eruptions.
When Volcanoes Kill Without Ever Waking Up Properly
Most people picture volcanoes as explosive, theatrical disasters—Mount Vesuvius burying Pompeii in 79 AD, Mount St. Helens decapitating itself in 1980. But carbon dioxide from volcanic sources operates on a different wavelength entirely. It seeps. It accumulates. It waits.
The CO2 at Lake Nyos had been dissolving into the lake’s bottom layers for decades, maybe centuries, pressurized by the water column above it like a massive carbonated beverage. Something triggered its release—possibly a landslide, maybe just the right temperature shift—and suddenly 1.6 million tonnes of gas erupted from the lake in about 20 seconds. The cloud moved at nearly 45 miles per hour.
Turns out, this wasn’t even a one-off.
Two years earlier, Lake Monoun—also in Cameroon—had released CO2 that killed 37 people. Same mechanism, smaller scale, equally horrifying. Scientists call these events limnic eruptions, and they’re specific to stratified lakes sitting atop volcanic vents. The gas builds up in lower water layers, then something disturbs the equilibrium, and the whole system destabilizes in what geologists describe with chilling understatement as “overturn.”
The Geography of Invisible Danger That Nobody Maps
Italy’s Solfatara crater near Naples emits about 1,500 tonnes of CO2 daily. Not explosively—just constantly, like a leaky faucet of death. In 2017, an 11-year-old boy fell into a sinkhole there and died almost instantly from CO2 inhalation. His parents jumped in to save him and died too. The gas had pooled in the depression, waiting.
Mammoth Mountain in California does the same thing. Since volcanic activity increased there in 1989, CO2 seepage has killed more than 100 acres of trees and created multiple “kill zones” where the gas concentration reaches lethal levels. In 2006, three ski patrol members fell into a cabin built over one of these zones and nearly died before being pulled out.
Wait—maybe the scariest part isn’t the dramatic lake eruptions or obvious volcanic zones.
It’s the gradual accumulation in enclosed spaces. Basements built on volcanic terrain. Caves. Old mines. Natural depressions in topography. CO2 is 1.5 times denser than air, so it settles into low points and just… sits there, invisible, odorless, waiting for someone to walk into what becomes an oxygen-depleted death trap. You don’t smell it. You don’t see it. You just get dizzy, confused, then unconscious, then dead—often in that order, sometimes faster.
Indonesia’s Dieng Plateau experienced this in 1979 when volcanic CO2 killed 142 people. The Democratic Republic of Congo’s Lake Kivu contains massive amounts of dissolved CO2 (along with methane), and roughly two million people live along its shores, essentially atop a geological time bomb that could dwarf the Nyos disaster.
The scientific response has been ingenious if slightly absurd: giant straws. Engineers installed degassing pipes in Lake Nyos that work like reverse fountains, bringing deep water to the surface where pressure drops and CO2 can fizz out safely into the atmosphere. It’s like burping a baby, except the baby is a lake and the burp could kill thousands if mismanaged.
The broader volcanic CO2 output globally is substantial—volcanoes release somewhere between 280 and 360 million tonnes annualy (tiny compared to human emissions of 37 billion tonnes, but still significant). The difference is that volcanic CO2 usually disperses into the atmosphere harmlessly. Usually.
Unless it doesn’t.
