Hellgrowth

Ignium-Wasche, more commonly known as Hellgrowth is a result of the Nether spilling forth into the overworld either through divine intervention, carelessness with portals or intentionally by people or gods.

Examples
Currently, Tarnwick are completly engulfed in Hellgrowth. Due to the emergence of pockets of hellgrowth underground, other cities have been taken over by hellgrowth.

Exceptions
Exceptions to the normal understanding of hellgrowth do exist. In some instances, gods overcome in anger may open rifts to the Nether and spread hellgrowth over the land. As well, some gods curse the land to forever be engulfed in hellgrowth, like in Asahiri's case. In some other cases, a group of settlers may perform a ritual to damage the land and/or curse it.

Asahiri has the appearance of a hellgrowth-engulfed city, but the situation is entirely different compared to other hellgrowths. The land has been cursed to forever be engulfed in hellgrowth and to have its air thick with dust and ash. This is unlike the other hellgrowths as any attempts to restore the city to its former state are futile as the dirt will turn into netherack and soul sand without fail.

Meta of Hellgrowth
Normally Hellgrowth is created through WorldEdit or the naturally generating Ruined Portal structure. But, it makes storytelling more interesting if we remove this detail.