The Dark Bloom was the name given by the people of Vasselheim to a phenomenon that started at some point after 20 Fessuran, during the apogee solstice of 843 PD.
Due to the strange magic and the shifting leylines, a surge of necromantic magic caused thousands of corpses in the catacombs beneath the city to rise again and begin to make their way to the surface. This was followed by a series of battles in which the forces of Dawn City defeated these undead, leaving the people of the Raven's Crest to apply the appropriate funeral rites to them for the second time. Given the massive number of undead rising, Vasselheim's soldiers sealed the caverns beneath the city, aware that there were surely more undead within, but unable to deal with them all at the moment.