Sunken slabs of ocean crust block flowing rock from moving further sideways, forcing it to turn downward and sink.

沉没的大洋板块阻止岩流向更深处移动，迫使它向下沉。

It's got big slabs of crust called tectonic plates that float on an ocean of slowly flowing rubbery molten rock.

它有巨大的地壳板块，称为构造板块，漂浮在缓慢流动的橡胶状熔融岩石的海洋上。