Portal:New Zealand/Selected article/Week 30, 2006

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The Tangiwai disaster was the worst rail accident in New Zealand history. It occurred on December 24, 1953, when the overnight express train between Wellington and Auckland, hauled by a KA class steam locomotive, passed over the Tangiwai railway bridge. The bridge, which had just minutes earlier been weakened by a lahar from Mount Ruapehu, collapsed, sending the train into the Whangaehu River.

Of the 285 people on the train that night, 134 survived and 151 died. Of those that died 20 bodies were never recovered; it is believed they were washed 100 kilometres down the river and out to sea.

The cause of the lahar was the collapse of a natural volcanic ash dam that had blocked the outlet of the crater lake on top of Mount Ruapehu. When it collapsed, the water from the lake mixed with the material from the ash dam and rushed down the mountainside in a flash flood known as a lahar. Until this disaster, the danger posed by lahars from Mount Ruapehu was appreciated by only a few scientists.