A bit of a backstory-ish info behind Zomu's unique magic.
Zomu has been known throughout history as "that guy throwing lava buckets everywhere". He (and Shaoron, in a bit later coming LPs) has a history of just burning every single person he comes across with lava during survival-based game-mods. It has actually become a running gag in the group.
So his Magma dive is quite direct reference to that.
Also Shao-san and Zomu-san are famous for their chaos-inducing antics when they're paired together, so having them to be best friends in the manga really makes me happy.