When Papatuanuku (The Earth Mother) was turned over to hide her face from Ranginui (The Sky Father) the youngest brother was still at her breast. As Papatuanuku lay facing the underworld Ruaumoko (The God of Earthquakes and Volcanoes) cried out in a rage as he was cold beneath her.
The brothers gave him fire to stay warm beneath the earth. Ruaumoko was still angry and he wriggled and thrashed about underground causing the Earth Mother to shake and so began the Earthquakes. He sent up flames of fire to pierce the earth and so began the eruptions, geysers, and the like.
Ruaumoko remains beneath his mother Papatuanuku and still wriggles about causing the earth to tremble and the mountains to spit forth their fire.
So Harken the Rumble of the EarthQuake God.
(this has been forwarded to me and I am unable to acknowledge the original source)