On Christmas Eve 1953, 16-year-old Bruce Thompson was lowered into the devastation where 151 people died in the Whangaehu River.
That night, a sudden lahar had swept down the river from the Mount Ruapehu crater, fatally weakening the Tangiwai bridge minutes ahead of the Wellington-Auckland night express train, much of which crashed into the river bed below.
"We lowered ourselves down and we came right beside carriage three and the locomotive. We searched that carriage three," Thompson recalled.
"It was completely cut in half and it was completely clear, there was no one in it, it was washed clean. I was later to learn that it could've held 56 people and there was four [who] survived."
Thompson said the river was strewn with boulders, trees, ice and thick mud from the lahar.
"I only had a silly little two cell torch, but the carriages that stayed on [the rails] on the other side, the southern side of the river, they had all their lights on and they put an eerie glow that seem to seep over to us on the northern side."
He said local farmers, rail and forestry workers as well as police braved terrifying scenes and dangerous conditions to pull survivors from the wreckage.
Thompson described a setting that would later become immortalised in the song Pillows of the Dead by a local, John Archer, who was 12 years old at the time.
"When you went on a train trip you always hired a pillow for about a shilling and these pillows were all sitting up on top of the lahar. But mixed in with these pillows were the bare backs of many bodies and a lot of the bodies got hooked up in willows. [They were] sort of riding high in the river and then when the river dropped down they were left hooked up in the [trees]," he said.
"All sorts of thoughts go back in different ways to that night."
Today's commemorative service was a chance to keep memories of the tragic events alive as the number of people who lived through it began to dwindle, Thompson said.
"All these sort of stories we put together and you realise how touching it is. I don't know if there'll be any tears today, they're all dried up, but there'll be a lot of feeling. A terrific lot of feeling 70 years on.
"I'm not getting any younger and trying to find people that could come along to the 70th, we felt, was very important because next time they have another one there's going to be even less of us."
Speaking from onboard a special train service to the accident site, creator of podcast Tangiwai a Forgotten History Hamish Williams said the day's memorial service would most likely be the last significant anniversary attended by survivors.
About 400 people were expected to attend the commemorative service and a wreath would be committed to the Whangaehu River from the train as it passed over the Tangiwai bridge in remembrance of those who perished.
"Many of the final few survivors left are in their twilight years and so this is a last chance to come together, perhaps, to be able to observe what was a incredibly traumatic event for them but also a very significant part of New Zealand's history," Williams said.
The outpouring of assistance in response to the tragedy had become the foundation of much of the country's emergency response network.
"So many people from around the immediate region and then right across New Zealand came together to help, and the idea that everyday New Zealanders might want to be able to put their hand up and be able to help out when needed has actually become the basis for how much of our emergency response is managed to this day," Williams said.
"That all began with Tangiwai.
"It's also a reminder that we live in a volatile environment. Volcanic eruptions, earthquakes, tsunamis and flooding are all a part of what it is to live in Aotearoa, and I think that it's a good reminder for us to look at our beautiful scenery but always remember that it comes with a degree of risk that we always need to address and be prepared for."
