我把这句话重新翻译一下: What is on top of this park is nothing compared to the giant reserve of magma that lies below.
【翻译】与下面大量的岩浆储备相比,这个公园上面的东西(景色)都不算什么。
1. what 为“融合性关系代词”,它身兼两职,既是先行词又是关系代词。what = the thing that 2. What is on top of this park is nothing = the thing that is on top of this park is nothing 3. compared to the giant reserve of magma that lies below:过去分词短语,作比较状语。 4. that lies below:magma 的定语从句。