The tangiwai disaster was caused by volcanic lahar coming from mt ruapehu crater.
on Christmas eve, the Wellington-Auckland night express crashed into the flooded Whangaehu river.
Over 150 people had died out of the 285 people on the train. This effected many families and got everyone wondering how it happened and who's fault is was.
This caused a flow of water, silt, boulders and debris down to the bridge just before the train arrived.
Because of the river overflow, the fourth pier had broken underneath the bridge causing the train tracks to break and the train half the train went under.
A lot of individual evidence was given and shown a year or two before the disaster but was ignored. Some people found evidence near the crator that the waters were rising that would cause a lahar. Some peopel think that it was the (governments fault for not making the bridge properly)- made people think of who was responsible for the cause. negligence on the railway and foundations. some thought is was an act of god. alarm system.