(citing a retelling by F. R. Schröder). In addition, Simek points to an Old Norse parallel in the figure of Örvar-Oddr, "who is rejuvenated after living as a tree-man (Ǫrvar-Odds saga 24–27)". Muspille, Heliand, and Christianity Theories have been proposed about the relation between Ragnarök and the 9th century Old High German epic poem Muspilli about the Christian Last Judgment, where the word Muspille appears, and the 9th century Old Saxon epic poem Heliand about the life of Christ, where various other forms of the word appear. In both sources, the word is used to signify the end of the world through fire. Old Norse forms of the term also appear throughout accounts of Ragnarök, where the world is also consumed in flames, and, though various theories exist about the meaning and origins of the term, its etymology has not been solved. Proto-Indo-European basis Parallels have been pointed out between the Ragnarök of Norse religion and the beliefs of other related Proto-Indo-European peoples. Subsequently, theories have been put forth that Ragnarök represents a later evolution of a Proto-Indo-European belief along with other cultures descending from the Proto-Indo-Europeans. These parallels include comparisons of a cosmic winter motif between the Norse Fimbulwinter, the Iranian Bundahishn and Yima. Víðarr's stride has been compared to the Vedic god Vishnu in that both have a "cosmic stride" with a special shoe used to tear apart a beastly wolf. Larger patterns have also been drawn between "final battle" events in Indo-European cultures, including the occurrence of a blind or semi-blind figure in "final battle" themes, and figures appearing suddenly with surprising skills. 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. Bertha Phillpotts theorizes that the figure of Surtr was inspired by Icelandic eruptions, and that he was a volcano demon. Surtr's name occurs in some Icelandic place names, among them the lava tube Surtshellir, a number of dark caverns in the volcanic central region of Iceland. Bergbúa þáttr Parallels have been pointed out between a poem spoken by a jötunn found in the 13th century þáttr Bergbúa þáttr ("the tale of