And this estimation is made without considering other types of caves, like, for example, inside glaciers or even volcanic caves, which are not karstic, but are formed by lava flows.
而这一估算还未包括其他种类的洞穴， 比如说，冰川洞穴，或者火山洞穴， 不是喀斯特洞穴， 而是由熔岩流动形成的。