noun
volcanic block
A solid fragment of rock ejected during a volcanic eruption, typically larger than 64 mm in diameter. Used in geology.
火山岩塊は噴火の際に火口から放出される。
Volcanic blocks are ejected from the crater during an eruption.
火山弾 (volcanic bomb) is a type of volcanic block that was molten or plastic when ejected, often taking on a streamlined shape, whereas 火山岩塊 is a more general term for any large solid fragment.
Compound of 火山 (volcano) + 岩塊 (rock mass, block of rock).