一个字:不。

让我用一个装满水的气球来解释一下。在这里，水代表了地球上的岩浆，而气球表面代表了地壳。

如果你戳破气球，水就会出来(类似于熔岩)。无论何时火山活动发生，地球表面的总质量都不会改变。因为熔融的岩石相当于液体，所以在地球内部没有空洞(想想充满水的气球)。
这里的总质量是常数，这意味着地球的大小不应该增加或减少。< / p > < p >。情况不一样，因为火山活动也会造成热量损失!< / p >

Earth is constantly loosing heat by various means and volcanism is one of them. As you you know: the colder the material, the more it contracts. So we can say it helps in contracting.

Note: There are radiogenic materials (Uranium, thorium, etc) which cause energy production in the mantle and thus expand the material volume. Hence there is a kind of equilibrium maintained for the transient time. On an earth scale this time could be of tens of thousands years.