1951 eruption of Mount Lamington
In early January 1951, a series of minor explosions and earthquakes rocked Mount Lamington, a volcano in the Australian-administered Territory of Papua and New Guinea (now in Oro Province, Papua New Guinea). Prior to the eruption, Mount Lamington was not recognized as a volcano due to the absence of historically recorded eruptions and dense vegetation cover.
Source: Wikipedia — 1951 eruption of Mount Lamington (CC BY-SA 4.0)