Mount Yasur is a volcano on Tanna Island, Vanuatu, 361 m (1,184 ft) high above sea level, on the coast near Sulphur Bay, northeast 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 several hundred years, although it can usually be approached safely. Its eruptions, which often occur several times an hour, are classified as Strombolian or Vulcanian. A large lava plain creeps across the valley at the base.
Mount Yasur is an easily accessible active volcano, and is a major Vanuatu tourist attraction. The Vanuatu Government monitors the level of volcanic activity in the interests of the public, both tourists and locals alike. This monitoring is carried out by the Vanuatu Geo-Hazards Observatory.
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.