Mountain has its own timetable

Were I a betting man, and were someone to have asked me last Tuesday which mountain would blow its volcanic stack next ... Ruapehu or Tongariro ... I would have put good money on Ruapehu.

Which would explain why my prowess at picking a Melbourne Cup winner is non-existent.

But choosing Ruapehu would have been a more than educated guess of course - considering that on Saturday last, GNS volcanologists were closely monitoring a partially blocked vent on that mountain which had caused a noticeable build-up of heat and pressure within it.

"A sudden release of the pressure may lead to an eruption," a duty volcanologist said.

And he was absolutely on the money ... except the wrong mountain obliged.

Just before 1.30 on Wednesday afternoon there was a brief but spectacular outburst of steam and ash from the Te Maari crater on Mount Tongariro.

It effectively exploded out of nowhere.

Unexpected and unannounced.

The only warning could have been the earlier murmurings of Ruapehu, although a scientist on the mountain said there was unlikely to be a link between the two.

Which I find odd, but they know best.

But they don't know when these things will happen.

They can loosely predict when temperatures rise or seismic ripples emerge, but just when, and how big, is the great unknown.

When they decide to vent steam, ash and rocks is pretty well a guessing game.

There were no hints at all last Wednesday morning that Tongariro would spark into life again, the way it did back on August 7 when the ash plume dusted the Bay in fine grit and caused about 30 flight cancellations and disruptions.

People walking the Tongariro crossing, including a group of Napier schoolchildren, had a first-hand look at the fury of the earth. They will have stark memories of their expedition, which could be the last for awhile as the "closed" signs went up around the mountain.

The activity died away quickly, but scientists said it was "quite possible" it could erupt again.

But they couldn't, and can't, say when.

So okay, we are 130km away from the mountains, why should we be concerned? Well, when Tarawera near Rotorua erupted in 1886 it was heard in Napier, and the glow could be seen.

And that's 300km away.

A major eruption, and a willing westerly wind, and we would wear it.

Indeed, I'm not a betting man, but one sound bet would be that these out-of-the-blue events may just be Mother Earth's little way of asking us if we are prepared for major upheaval.

"You got a plan?" she is asking.