KEY POINTS:
For the past couple of years, the world's volcanologists must have watched developments on Mt Ruapehu with a high degree of interest and no little puzzlement. It is not often they have the opportunity to scrutinise a totally predictable mishap. But, with the mountain's crater lake now only 2.8m below the top of a dam of ash and rocks formed by the 1995-96 eruptions, there is a strong possibility that, some time in the next few weeks, it will burst and one million cubic metres will sweep down the Whangaehu Valley. That would be a lahar almost twice the size of the one that caused the Tangiwai disaster in 1953 in which 151 people on an overnight train died - enough to capture anybody's attention.
The volcanologists' bemusement relates to what New Zealand has done, or, more precisely, not done, to prepare for this inevitability. In 2003, it was suggested the mudflow could be controlled if bulldozers were to dig a 100m trench, thereby allowing the lake water to drain harmlessly. This apparently straightforward $200,000 job was rejected by the Minister of Conservation, Chris Carter, on the grounds that it would be dangerous for those who did the work.
Maybe so, but the minister did not say it would not work. More likely, he was swayed by the opposition of local iwi, who maintain crude cuts in the mountain's summit would be an affront to their spiritual values.
The world's volcanologists have, therefore, watched as a cultural hurdle to a piece of engineering that would avert a potentially devastating lahar has produced a decision based on political factors. It must surely have made no sense to them, and it will make no sense to those whose livelihood and, possibly, lives are threatened when the inevitable happens. A channel should have been dug in 2003-04, when it could have gone through solid older lava. Now, it would have to pierce the much weaker dam dumped by the 1995-96 eruptions. But that should not be ruled out if the burst does not occur this summer, delivering a probable year's reprieve.
Instead of taking the logical course, the Government has concentrated on bolstering safety measures. These include strengthening bridges and installing an alarm system that warns a lahar is on the way. Response plans have been prepared to evacuate the area and close all at-risk bridges, roads and railway lines, and a 300m-long stopbank has been built to stop the lahar spilling into Lake Taupo's catchment.
This is all well and good. But nature specialises in confounding such planning. It never acts quite as expected. If the lahar occurs as predicted, there may, indeed, be minimal damage and no loss of life. But what if it were triggered by a major earthquake that also disrupted the early warning system? At best, such systems provide only a limited warning - 90 minutes in the case of a mudflow rushing towards the Tangiwai bridges. They do not stop infrastructural damage, or organise the evacuation of an area that is often thickly populated with trampers, canoeists and skiers.
Local authorities in the area have long doubted the chances of an effective evacuation. They were strong advocates of a trench. They have complained about cultural concerns being given a higher priority than the risk to life. It is they who will have to pick up the pieces after the lahar has done its work. Having had their advice rejected, they will have good reason for seeking multimillion-dollar support from the Government.
Scientists, for their part, will get the rare opportunity to observe a natural process unhindered by human hand. Doubtless, they will be grateful for the opportunity. At the same time, they can marvel at the eccentric thinking that allowed this to happen.
