KEY POINTS:
Environmentalists are inordinately fond of an idea they call the precautionary principle. Under this principle they argue for all sorts of costly measures against remote or dubious risks to the planet, insisting it is always better to be safe than sorry. It is not always better in fact.
If the economic cost of precautions is out of proportion to the possible harm, people are better off living with the risk. But, oddly, our environmental conservators did not invoke the precautionary principle against Mt Ruapehu's lahar.
The lahar has happened exactly as predicted. On Sunday, when the mountain's Crater Lake breached the dam created by the debris of its latest eruption, the lahar flowed down the slopes and along the stream beds as expected. Conservation Minister Chris Carter says he is delighted. Mightily relieved is probably a more accurate description. Certainly that will be the Prime Minister's state of mind.
As a risk-averse politician, she must have had some nervous times after her Conservation Minister rejected proposals to release the rising lake before it produced a lahar. Had the dam burst differently than his department predicted and caused serious damage or death, the Government could have paid a high political price. The blame would have lain with its excessive deference to Maori and environmental spirituality which held that it would be somehow wrong to interfere with nature on the mountain.
Mr Carter insisted it would be too risky to put earthmoving machinery on the crater rim, and perhaps it would have been, near the end. But much earlier, when the lake began rising after the 1995 eruption, it surely could have been done. How hard can it be to clear a gap in newly deposited volcanic debris? If heavy machinery cannot operate up there, why could the dam not be breached with explosives?
Mr Carter has praised all agencies involved in monitoring the lahar, strengthening the structures in its expected path and issuing the warnings when it happened. "We now have a robust system to manage this kind of event," he said. "To do so with a great degree of advance warning, with the least amount of damage to people and property, is the ideal situation."
No it is not. The ideal would be that no warnings and inconvenience were necessary because his department had ensured the lake could continue draining normally after the last eruption. It is an interesting ideology that holds an element of avoidable danger to be part of the ideal. Perhaps the same principle could be applied to global warming; let's not try to prevent a build-up in greenhouse gases, let the mean temperature rise and trust that with plenty of warning and a bit of engineering, humans can avoid harmful consequences.
That may indeed be the most sensible response to climate change but it is not the one the Government advocates. Its avowed goal of carbon neutrality will impose severe costs on carbon-belching industry.
Sooner or later Ruapehu will erupt again and create a new dam where the lake has been draining. It is then that the question we are posing today will become urgent. Ought we put a pipe through the debris, if not remove it entirely, or stand and watch again while nature takes its course?
We may have been lucky this week. The department believes the natural dam gave way slowly over 45 minutes, releasing water in a series of pulses rather than a sudden cascade. Had 1.2 million cubic metres of water fallen from the mountain in a single rush, it might have taken more than mud and rock with it; it might have done enough damage to take the Conservation Minister and the Government down too. They must be relieved.