Eruptions at Mt Tongariro could continue for months, if not years, scientists say, and they are still expecting Ruapehu to let off more steam.
The eruption at Tongariro's Te Maari crater about 1.30pm on Wednesday sent a 4-kilometre plume of ash into the air and lasted about five minutes, GNS Science confirmed yesterday.
It monitored the mountain closely all day yesterday, saying activity was at a low level.
However, there remained a significant probability of a sudden eruption within the next week.
"Progressive pressure may build up over time and we think that's what's happening," GNS vulcanologist Nico Fournier said.
Taranaki Civil Defence issued advice yesterday to residents on how to cope with ash falls.
Taranaki senior emergency management officer Shane Briggs said people should stay indoors, close all windows and doors and turn off the air conditioning and heat pumps.
"If people are outside they need to find cover, preferably in a car or building," Mr Briggs said.
People with respiratory problems such as bronchitis or asthma would be most affected by ash fall, he said.
Dust masks or handkerchiefs should be worn outside. Eyes should also be protected with goggles or glasses and people should avoid wearing contact lenses, he said.
"That can create some irritation and abrasion in the eye."
Keep all pets indoors and, as with any emergency, stay up to date with instructions from the authorities, he said.
Driving around in the ash should be avoided because it created visibility problems, he said.
Small amounts of ash falling should not create too many problems so long as people took the advised precautions, he said.
"It's only when we start getting thick ash that we have problems."
A few millimetres of ash on the ground would not be a problem for farm animals and crops, he said.
Federated Farmers has a list of recommendations on its website.
Measures ranged from ensuring farm insurance cover was adequate to maintaining a resilient power supply.
In 1998 Massey University scientist Shane Cronin briefed Taranaki farmers and civil defence controllers on the agricultural impact of the 1995 and 1996 Mt Ruapehu eruptions.
He said after the eruptions more than 2000 sheep and cattle died because of high sulphur levels in the pasture from ash clouds.
If farmers were not prepared, this could happen in Taranaki, he said.
"Farmers should get out supplementary feed.
"Lots of animals stop eating because it smells really awful," Dr Cronin said.
- Taranaki Daily News
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