Mazuku

thumb|Mazuku forming in a low morphological depression on the foothills of Mt. Amiata, Italy, where CO2-rich fog accumulates in a ditch Mazuku (Swahili for "evil winds") are pockets of dry, cold carbon dioxide-rich gases released from vents or fissures in volcanically and tectonically active areas, mixed with dispersed atmospheric air and accumulating in typically low-lying areas. Since carbon dioxide (CO2) is ~1.5 times heavier than air, it tends to flow downhill, hugging the ground like a low fog and gathering in enclosed spaces with poor ventilation—such as lava tubes, ditches, depressions, caves, and house basements—or in the stratified water layers of meromictic lakes if a water column exists. In high concentrations (≥ 1% by volume), they can pose a deadly risk to both humans and animals in the surrounding area because they are undetectable by olfactory or visual senses in most conditions.

Mazuku primarily occur on the northern shores of Lake Kivu to either side of the twin towns of Goma (Democratic Republic of the Congo) and Gisenyi (Rwanda), where local communities use this term in their vernacular (Kinyabwisha language) to describe the dangerous gases. They believe mazuku occur in cursed locations where invisible forces roam, silently killing people in the night while they sleep. In many places where mazuku occur, CO2 levels fall during daytime but can rise to significantly dangerous concentration levels of about 90% at night, early mornings, or evening hours, posing a great threat. This is because at night the atmospheric temperature drops and wind speeds significantly reduce. These conditions slow the dispersal of these heavy gases into the atmosphere, allowing them to accumulate in lower-lying areas, such as valleys and depressions.