Hvergelmir is the wellspring of cold in Niflheim in Norse mythology. The well is guarded by Ivaldi and his sons who are charged with the defence of Hel against the incursions of the storm giants. All cold rivers are said to come from here, and it was said to be the source of the eleven rivers, Elivagar. The name means approximately "The seething cauldron". Above the spring, the serpent Nidhogg gnaws on one of the roots of the world ash, Yggdrasil.