And one thing that's a threat to them are pyroclastic flows, when a mix of lava blocks, ash and volcanic gas rush down the slopes of a volcano.

对它们构成威胁的是火山碎屑流——即熔岩块、火山灰和火山气体的混合物冲下火山斜坡（的过程）。

He uncoiled a cord of the thickness of a finger, and four hundred feet long; first he dropped half of it down, then he passed it round a lava block that projected conveniently, and threw the other half down the chimney.

他展开一根手指粗细、四百英尺长的绳子。他先把一半扔下去， 然后绕过一块方便突出的熔岩块，把另一半扔进烟囱。