When the lava drains out, the outer shell remains, forming a lava cave.

当岩浆外泄时，外层硬壳仍然保存着，由此形成一个岩浆洞穴。

Space scientists have long identified these lava caves as a likely site for human habitation on the Moon, because the thick walls and ceiling offer protection from the harsh radiation striking the Moon's surface.

太空科学家长期以来一直将这些熔岩洞穴确定为人类在月球上居住的可能地点，因为厚厚的墙壁和天花板可以保护免受撞击月球表面的强烈辐射。