source: Falling into lava would be a pretty hot mess - The Verge

hot molten or semifluid rock erupted from a volcano or fissure, or solid rock resulting from cooling of this.

〘地〙 溶岩〘流体, もしくは固化した岩石をさす〙; C〖～s〗 溶岩層

mid 18th century: from Italian (Neapolitan dialect), denoting the lava stream from Vesuvius, but originally denoting a stream caused by sudden rain, from lavare ‘to wash’, from Latin.