The Ragnarok (ラグナロク Ragunaroku) was a cataclysmic event which was foretold to destroy all the Nine Realms according to Norse mythology. Its fallout is the central focus of the events of the film Mouchuu: Little Kaiju of Pranks.
The dissolving of the Yggdrasil and the rampage of Surtr resulted in the destruction of the Nine Realms with the exception of Alfheim and Midgard (Earth).