expression, godan verb (-su)
pile up; form a huge pile
Describes things accumulating into a large heap, often used for physical objects like books, snow, or garbage. The phrase emphasizes the size or abundance of the pile.
机の上に書類が山をなしている。
Documents are piled up on the desk.
雪が山をなして積もった。
The snow piled up into a huge mound.