Short answers, pulled from the story.
Ragnarök is a foretold series of catastrophic events in Norse mythology that includes a great battle in which major gods including Odin, Thor, Týr, Freyr, Heimdall, and Loki perish, followed by the submersion of the world underwater. After the destruction, the world rises again cleansed and fertile, and two human survivors named Líf and Lífþrasir repopulate the earth.
Ragnarök is attested primarily in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson. The most detailed account appears in the poem Völuspá, in which a female seer recites the events to Odin, and in chapter 51 of the Prose Edda book Gylfaginning.
Among the gods, Víðarr, Váli, and Thor's sons Móði and Magni survive, along with Baldr and Höðr who return from Hel. Two humans, Líf and Lífþrasir, survive by hiding in the wood Hoddmímis holt, sustaining themselves on morning dew. The scholar Rudolf Simek theorizes that Hoddmímis holt is an alternative name for the world-tree Yggdrasil.
The name Ragnarök is generally interpreted as the final destiny of the gods. Its first element, ragna, is the genitive plural of regin meaning the ruling powers or gods; the second element rök has meanings including fate, doom, and destruction. A variant form, ragnarøkkr, meaning twilight of the gods, gave rise to the German word Götterdämmerung, which Richard Wagner used as the title of his 1876 opera.
Several carved stones have been identified as depicting scenes from Ragnarök. Thorwald's Cross from Kirk Andreas on the Isle of Man, dated by Rundata to 940, shows a figure interpreted as Odin being consumed by the wolf Fenrir. The Gosforth Cross dated to 920-950 in Cumbria, England, depicts Víðarr tearing open the wolf's jaws. The 11th-century Ledberg stone in Sweden also shows a figure with his foot at a beast's mouth, interpreted as Odin's final moment.
Several scholars have proposed a connection. Hilda Ellis Davidson theorizes that the post-battle imagery in Völuspá, including the sun turning black and flames touching the heavens, resembles accounts of Icelandic eruptions, citing the 1783 Laki eruption as a close parallel. Research by Mathias Nordvig and Felix Riede connects the myth to the volcanic winters of 536-550 AD, which produced extended darkness and triggered settlement shifts across Scandinavia.