Mount Yasur is an active volcano on Tanna Island, Vanuatu (lat/long 19.52 S, 169.43 E) with a height of 361 m (1,184 ft) above sea level, located on the coast near Sulphur Bay. It lies to the southeast of the taller Mount Tukosmera, which was active in the Pleistocene. It has a largely unvegetated pyroclastic cone with a nearly-circular summit crater 400 m in diameter. It is a stratovolcano, caused by the eastward-moving Indo-Australian Plate being subducted under the westward-moving Pacific Plate. It has been erupting nearly continuously for over 800 years, although it can usually be approached safely. Its eruptions, which often occur several times an hour, are classified as Strombolian or Vulcanian.

The glow of the volcano was apparently what attracted Captain James Cook on the first European journey to the island in 1774. Today the mountain is a sacred area for the John Frum cargo cult. Members of the cult revere John Frum, a deified messenger who foretold the bringing of wealth to the island by American forces, and believe he resides in Mount Yasur with his countrymen. The village of Sulphur Bay, the center of the movement, claims the volcano as part of their territory.