Mana Founts are giant mountains across Unios that connect to its core. The core of Unios is a giant ball of dense aer. Occassionally, Mana Founts eject copious amounts of it into the atmosphere. Their names are a holdover of a time when "air" and "mana" were thought of as two different things.
Especially dense aer is not good for the body, so people who are near Mana Founts when they erupt tend to find themselves feeling aersick.
The far northern nation of Ekaska is notable for being home to a unique type of mana found called a volcano, due to the high concentration of fire and earth aer in the area that combines to form magma whenever it erupts.