By ELEANOR BLACK
An alarm to warn people at Turangi and on the Desert Rd in case of a mudslide from Mt Ruapehu's crater will be installed in 2002, six years after the danger became known.
Dr Harry Keys, advisory scientist for the Department of Conservation's Taupo-Tongariro conservancy, said there was no risk of a lahar - a huge spill of mud, water and ash through the thin crater wall - for at least another three years, as the crater lake was only a third full.
But it was now filling faster because of warmer weather and care had to be taken to prevent another Tangiwai, the 1953 rail disaster in which 151 people were killed when a lahar washed away a railway bridge.
The crater lake was emptied during Ruapehu's 1995 eruption.
Scientists first realised the danger posed by the weakened crater wall - in some places made of rock and ash debris - in 1996, when the lake started to refill, Dr Keys said.
The risk to the nearby rail bridge and road bridge was very high, but the $100,000 alarm - based on two to four sensors that pick up vibrations in the earth - would give two hours' warning to people at Turangi before disaster struck.
The alarm system won the support of Conservation Minister Sandra Lee in May, but only received the nod from Taupo District Council's Turangi-Tongariro Community Board this week.
Dr Keys said there was no reliable warning at present to alert people of a flood of water and ash into the Tongariro River catchment and overflow on to the Desert Rd.
Motorists, and anglers wading up to their chests in the river, would be at risk if the crater wall broke.
Scientists are also considering building a stopbank to protect the river from overflow.
In February, scientists from the United States Geological Survey will view and assess the crater.
Though lahars were a regular occurrence and did not often put people at risk, Dr Keys said it was important to keep the worst outcome in mind.
More than 30 lahars occurred at Mt Ruapehu in 1995 when the volcano erupted.
Crater risk warning for town at last
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