Wikipedia
In geology, a mazuku ( Swahili: evil wind) is a pocket of carbon dioxide-rich air that can be lethal to any human or animal life inside. Mazuku are created when carbon dioxide accumulates in pockets low to the ground. CO is heavier than air, which causes it to stay close to the ground, and is also undetectable by human olfactory or visual senses in most conditions.
Mazuku can be related to volcanic activity or to a natural disaster known as a limnic eruption. In the first case, noxious gases are released from the Earth's crust into the atmosphere, whereas in the second case the gases originate deep in a lake and boil rapidly to the surface. Because of their nature as sporadic and subtle events, few mazuku have been recorded, but there is a growing understanding of them based on historical and fossil evidence.