Mount Ruapehu caused the 1953 Tangiwai disaster when a lahar destroyed a railway bridge.
On 24 December 1953, a lahar from Mount Ruapehu’s crater lake swept down the Whangaehu River. The surge destroyed the Tangiwai railway bridge shortly before the Wellington-to-Auckland express train reached it. The train plunged into the river, killing 151 people in New Zealand’s deadliest railway accident.
The lahar resulted from the failure of a natural barrier around Ruapehu’s crater lake. Such events are a major hazard at Ruapehu because water, volcanic ash, and rock can move rapidly down river valleys even when the volcano is not producing a large explosive eruption.
Ruapehu is New Zealand’s highest volcano and the highest mountain on the North Island. It is part of Tongariro National Park and has several summit peaks. Mount Ngauruhoe and Mount Tongariro are nearby but are separate volcanic centres, not the volcano responsible for Tangiwai.