noun
volcanic bomb
A geological term for a mass of molten rock ejected during an eruption that solidifies in flight, often taking on a streamlined shape.
火山弾は噴火の勢いで遠くまで飛ばされることがある。
Volcanic bombs can be thrown far by the force of an eruption.
Compound of 火山 (volcano) and 弾 (bullet, projectile), literally 'volcano bullet'. The term is a direct calque of the English 'volcanic bomb'.