with all that lightning they look live living monsters...maybe this is what the Norse mythology means by fire giants ,who incidentally are said to return to join the fray for Ragnarok
from wikipedia
-http://en.wikipedia.org/wiki/Ragnar%C3%B6k
Volcanic eruptions
Hilda Ellis Davidson theorizes that the events in Völuspá occurring after the death of the gods (the sun turning black, steam rising, flames touching the heavens, etc.) may be inspired by the volcanic eruptions on Iceland. Records of eruptions on Iceland bear strong similarities to the sequence of events described in Völuspá, especially the eruption at Laki that occurred in 1783.[52] Bertha Phillpotts theorizes that the figure of Surtr was inspired by Icelandic eruptions, and that he was a volcano demon.[53] Surtr's name occurs in some Icelandic place names, among them the lava tube caves Surtshellir, a number of dark caverns in the volcanic central region of Iceland.