Mt Tongariro erupts for first time in over 100 years
Scientists have declared a ''watch this space scenario'' for Mt Tongariro and say a larger, molten eruption is possible if volcanic activity continues.
The volcano rumbled into life at 11.50pm last night, sending ash and rock a kilometre into the air, prompting a potential threat warning for central North Island regions.
Though there had been no escalation in background seismicity today, the mountain could blow its top again depending on what is causing the unrest, GNS scientist Brad Scott said at a press conference in Taupo this afternoon.
''If it is steam driven ... it's unlikely to do much more because once the initial pressure drops occurred you'll just get smaller activity.
''If it is being driven by a longer term magmatic process with molten material being intruded into the volcano it may take days to weeks before that sort of shows itself.''
Ash samples will determine what is driving the activity, he said. ''It's really just a watch this space scenario.''
The "small scale" eruption was a total surprise, with the volcano last erupting in 1897.
Mr Scott said there was strong seismic activity for about 15 to 20 minutes after the eruption, however in the 24 hours prior and hours since, there had not been any significant activity.
There had been no lahars or lava flows, and while it was too early to predict what might happen next, GNS scientists expected heightened activity which could go on for weeks.
GNS Science revised its colour code from red to orange, or from "eruption is forecast to be imminent" to "volcano is exhibiting heightened unrest with increased likelihood of eruption".
GNS was monitoring the activity on the mountain. It had also collected ash samples for assessment.
The agency wasn't yet able to confirm exactly where the eruption came from but it was most likely near the Te Mari craters, near Ketetahi hot springs, on the northern side of the mountain.
The eruption was believed to have lasted only one or two minutes and was followed by a series of small earthquakes.
It generated an ash plume and ash fall, Scott said. Five to 15 milimetres of ash blanketed nearby properties.
Police urged residents to check water supplies to make sure they were not contaminated.
There was no immediate health risk to the community and there was no need to remain inside or keep doors and windows closed, police said.
Only people in the local vicinity of the eruption who had a predisposition to respiratory issues were at risk, police said.
Three people were evacuated from Mangatepopo Hut in Tongariro National Park and other huts were still being searched by police and Conservation Department staff.
Tuwharetoa co-ordinator Bubs Smith said 24 people from the settlement were evacuated.
A few had stayed behind to tend to stock, he said.
The trust had been preparing for this type of eruption for the last week or so due to the recent activity in the area, he said.
Ski fields were open for business as usual.
There were reports of some schools having masks ready to hand out to children if the situation worsened.
'WE CAN'T REALLY PREDICT WHAT THIS WILL LEAD TO'
Eruptions had occurred on Tongariro intermittently from 1855 through to 1897, and it could not be ruled out that this was the start of a prolonged period of activity in the area, GNS vulcanologist Michael Rosenberg said.
"We have to expect the unexpected. We really can't predict what this will lead to."
Recent volcanic unrest at White Island was unrelated and coincidental to last night's eruption at Tongariro.
Truck driver Tama Coker was heading across the Desert Road while the eruption was happening and said the noise was like a train.
"There was a big flash," he said.
"I thought it was lightning and then it started raining sand. It was pretty thick. I heard it rumbling like a train."
Coker said that when he drove through the Desert Road he could not see the white lines on the road.
"I could just see the yellow glare on the mountain. I only had visibility of about 10 to 15 feet in front of me. It was a bit scary.
"It's something I'll probably never see again in my lifetime."
He said the sand-like ash had covered his truck, and the sign writing on the trailer was barely visible.
Local resident David Bennett who lives on the southern shores of Lake Rotoaira, about 6km away from the eruption, said he heard and saw the mountain erupt just before midnight last night.
He considered himself fortunate no rocks landed on his house last night.
"There were rocks being thrown out. It was like thunder and lightning and fireworks," Bennett said.
"It was spectacular. There were rumbling sounds and thunder and lightning coming out from the base of the eruption," Bennett said.
A few locals did drive to the Hirangi Marae in Turangi but most just stood and watched the spectacular show.
"It's a volcano. If it goes. It will go. We'll all be vapourised. Ruapehu and Ngauruhoe have erupted regularly over the years. Now it is Tongariro's turn."
Bennett's wife Robyn said she had not been able to sleep last night following the spectacular eruption.
"It looked like a huge mushroom cloud. There's a very strong sulphur smell in the air and it was very hard to breathe last night."
Robyn Bennett said she and her husband could still hear the mountain rumbling from their home this morning.
"The ash plume is rolling down the side of the mountain. I feel safe and I am not leaving."
Robyn Bennett said if the mountain did blow "our house will be in the middle of it. The lava flow will come down the valley towards us."
She could see three new vents from her home.
"They each look to be the size of the Ketetahi Springs."
Adventure HQ employee Kerry Wakelin said she took her dogs for a walk about 11.50pm last night.
"I saw flashes and lightning and a big black cloud. I thought it was a big storm," Wakelin said.
She had worked at the Whakapapa Ski Field during the major eruptions on Mt Ruapehu in the mid-1990s.
"When Ruapehu blew back then I had my bags packed and was freaking out. Last night I went to bed and had a good night's sleep," Wakelin said.
"The latest eruption is like a big old giant who has woken up, farted, rolled over and gone back to sleep," Wakelin said.
Some flights to and from Gisborne, Rotorua, Taupo, Napier and Palmerston North have been delayed or cancelled due to the eruption.
"We will not fly through ash and are constantly taking guidance ... to ensure we can continue to carry passengers where safe routes and altitudes are available," Air New Zealand said.
About 20 domestic flights in and out of Auckland airport have been cancelled, and 22 have been delayed.
- Michelle Cooke, Mike Watson and Danya Levy