Photo galleryKEY POINTS:
Scientists say Mt Ruapehu's activity is unpredictable and its status will be monitored over the crucial next few days.
But optimistic ski operators, confident the volcano has settled, are promising that it will be business as usual today.
Skifields on both sides of the mountain were closed yesterday although the road to the Top O' the Bruce was opened about 8.30am.
Ruapehu Alpine Lifts, which runs both the Turoa and Whakapapa skifields, lost up to $200,000 of chairlift revenue.
Some families yesterday made the most of the perfect alpine weather and played on the lower slopes, while others took pictures of the darkened area around crater lake.
GNS Science vulcanologist Brad Scott said yesterday that one of the features of the eruption, lahar, and earthquake had been its "ballistic" nature, meaning rocks and debris had been fired "like cannonballs" from the crater lake.
They made "pimple and pock marks" in the snow.
He said the eruption was a "blue sky" event, meaning no data had indicated it was about to occur. Asked what caused such an event, he said, "That's the $64,000 question.
"The process becomes unstable in the background.
"One thing that has been happening is the heat flow through the vent into the crater lake has been declining."
Temperatures in the lake had plummeted from 40C to 13C over the past 18 months, he said.
This indicated a build-up of pressure.
The Department of Conservation was advising people against sightseeing treks to the upper slopes yesterday, and said the warning would remain in place for about the next three to seven days.
"Our message to anyone out there is that no one goes above the 2km mark [above the skifield boundary]."
Many known viewing spots for climbers were well within the hazardous area, department spokesman Dave Wakelin said, and there was noguarantee what would happen over the remainder of the week.
"Volcanoes make up their own mind as to what they are going to do."
He said the material that could spew out of the mountain was dense and if people wanted to play the odds with "bombs" that were typically ejected, they should also think about buying a Lotto ticket.
Ruapehu Alpine Lifts general manager Dave Mazey said that if things remained as they were yesterday, both Whakapapa and Turoa would be open to cater to thecrucial school holiday crowds.
However, the decision over whether to open was a "collective" one, made in consultation with the department and with the advice of GNS Science.
The company would have missed between $150,000 and $200,000 of revenue from lost business yesterday, he said.
No part of the skifield had been affected, although there were rumours that the far west area of the field,for advanced skiers and boarders,was badly damaged.
One person said that unless there was a southerly blast in the next few weeks, there would be no further skiing in that area this year.
The season is due to end on the last day of October.
Mr Mazey was philosophical about the lost business yesterday, on what would have been a perfect day's skiing for holidaymakers.
"That's the nature of the mountain."
Holidaymakers at the Ngauruhoe ski lodge on Mt Ruapehu yesterday described their late evening evacuation on Wednesday.
Nadene van der Maas of Auckland said she and her three children made their way down to the Chateau about 10.15pm, after the alert from their lodge manager came in. All 33 people in the lodge were told to leave.
"I thought it was a joke at first, we were all lying in bed," Mrs van der Maas said.
"Then I realised it wasn't.
"We didn't hear feel or see anything. There was no warning at all that something was wrong."
Groups from other lodges also gathered at the Chateau, and people's reactions were mixed.
Some children were frightened and began crying, some people chatted away in a state of anxiety and excitement, and others remained calm, she said.
Her daughter Emma, 15, said she was "quite devastated" by the closure of the chairlifts yesterday. "It's the best weather we've had for a while."
Eruption: The Impact
* An area covering a 2km radius around the summit of Ruapehu felt the impact of the eruption.
* Rocks and debris were blasted "like cannonballs" from the crater lake.
* A factor in the eruption could have been the steep fall in the lake's temperature from 40C to 13C over the past 18 months, which in turn indicated a build-up of pressure under the lake floor.
