Beneath this active layer is a second layer called "permafrost", which is frozen all year around, and is impermeable to water.

在这一活跃层下面，是被称为“多年冻土”的第二层，终年冻结，不透水。

youdao

There're two reasons for this: first, they live in the active layer, which, remember, contains water that doesn't penetrate the permafrost.

造成这种情况的原因有两个：首先，它们生活在活动层中，请记住，活动层中包含的水不会渗透永久冻土。

youdao