Mt Ruapehu lahar warning system a close call - Tangiwai: A Forgotten History, episode four

The Tangiwai National Memorial, designed by government architect F. Gordon Wilson, was unveiled at Karori Cemetery on 26 March 1957. Photo / Dean Purcell

On the 70th anniversary of New Zealand’s worst rail disaster, a new Herald podcast recalls the tragedy and lessons of Tangiwai. In episode four, host Hamish Williams learns how long we took to heed the warnings

For two years running - 1995 and 1996 - New Zealand received dramatic reminders Mt Ruapehu really is an active volcano.

Yet, despite global coverage - including a small group of people travelling to the rim of the crater to get a better look - no immediate action was taken to increase monitoring of the mountain for public safety.

It took another six years before this changed and the decision ultimately came down to a single conversation.

When Chris Carter became Minister of Conservation in 2002 he took the unusual step of reaching out for a debrief from his predecessor Sandra Lee. In conversation at her Waiheke home, she told Carter one of the things that kept her awake at night was the threat of another lahar from the crater lake on Ruapehu.

Carter found that Lee wasn’t alone. UK risk management specialist Dr Tony Taig had completed a residential risk report for the Ministry of Civil Defence on the dangers of the lahar, based on the events of 1953.

Carter took the report’s recommendations for a warning system to then-prime minister Helen Clark, who gave him the green light to go ahead.

A multi-agency team installed an electronic monitoring system on the crater lake, which would give an immediate warning if it collapsed, and extensive seismic monitoring for volcanic activity on the mountain. The plan addressed pollution from the lahar into the Taupo river catchment, built a 300-metre protective stop bank, installed gates, lights and signs on State Highway 1 and 49 to stop traffic and massively strengthened the Tangiwai rail bridge.

The work took two years but by 2004 Carter had gained a critical 90-minute window to prevent having anyone or anything in the pathway of the lahar.

In 2007, the crater lake broke and the monitoring system was triggered. All of the preparation put in place three years earlier went according to plan. There was no major destruction, no injuries and no loss of life.

Carter acknowledges in geological terms it was a close call.

He believes it took 50 years to address the risk posed by the crater lake because politicians were always putting it in the too-hard basket.

“We were lucky to have a prime minister that recognised the risk and spent a considerable amount of money making that community and our country safer as a result.”

Tangiwai: A Forgotten History is available at iHeartRadio, Apple Podcasts, Spotify or wherever you get your podcasts. The series was made with the support of NZ On Air. For video and photos, go to nzherald.co.nz/tangiwai