While in his transformed state, Rōshi creates an enormous torrent of lava that violently erupts from the ground, before rushing upwards towards the target.
The summit of the Mountain of Flowers and Fruits (花果山, Ja: Kakazan, Ch: Huāguǒshān) is the birthplace of Sūn Wùkōng, the main character of the Chinese novel Journey to the West. The mountain is located on a volcanic island. The Four-Tails, of course, is based on Sūn Wùkōng and the Dragon Ball series, which in turn is also based on Journey to the West.
When written as 火山, kazan means 'volcano'. Then, if you substitute 果 with 火, you get fireworks (花火, hanabi). 果 is also the Japanese for the Phala.