Lahar was '25 per cent bigger than Tangiwai'

Mud and debris lay around the monument to the Tangiwai rail disaster of 1953. Photo / Alan Gibson

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Sunday's lahar from Mt Ruapehu was 25 per cent bigger than the flow that caused the 1953 Tangiwai disaster, preliminary research suggests.

Scientists are rubbing their hands together with glee at the wealth of information they have been able to compile following Sunday's dramatic lahar.

Researchers from GNS Science and Massey University have spent the past few days collating data on the event as part of a $1 million research programme.

"All of our years of effort have paid off. We have collected a world-class dataset that will make this the best-studied lahar ever," said project leader Dr Vern Manville, of GNS Science.

Early results show the lahar was 25 per cent bigger than the devastating 1953 Tangiwai flow.

On Christmas Eve 1953, an enormous lahar roaring down from Ruapehu destroyed the rail bridge at Tangiwai, plunging an express locomotive and carriages into the torrent, with the loss of 151 lives.

Sunday's lahar was predicted months ago, as the crater lake at Mt Ruapehu had been rising swiftly and the dam holding it back had begun to leak water at its base.

Experts predicted the water would force a rupture this month or next and their forecasts proved spot on.

The dam disintegrated on Sunday morning, allowing the pent-up acidic lake water to gush out.

Shane Cronin, leader of Massey University's lahar science programme, sent 16 staff and student volunteers on Sunday to track the lahar downstream and to collect eye-witness records of its behaviour as it poured down the Whangaehu Valley.

"Although the lahar is over, the real work is just beginning for us," Dr Cronin said.

Information was being shared between all of the agencies that had measuring equipment and observers along the river, including the Department of Conservation, Horizons Regional Council, Ontrack, and Genesis.

Video and still images captured by media and the public would also be valuable, Dr Cronin said.

The lahar had attracted "considerable interest" from overseas researchers, with groups from Hawaii, Japan, France and Britain taking part in the scientific response.

The research programme is funded by a Marsden grant from the Royal Society of New Zealand, the Foundation for Research Science and Technology, and the Earthquake Commission.

- NZPA