It happened in the mid 1990s and it could easily happen again.
The NZ Geological Survey has issued a press release saying that aviation in New Zealand could also be affected by ash from New Zealand’s active volcanoes and that an eruption the same size as the last one at Lake Taupo could seriously affect 200,000 people in the centre of the North Island.
Mount Ruapehu typically has small eruptions every dozen or so years and larger eruptions about twice a century. Many people will experience it at least once in their lifetimes and should start planning for it because even minor eruptions can cause a lot of problems. In the mid 1990s no-fly zones were declared in the North Island and 11 airports closed, causing disruption to thousands of passengers:
“The chaos caused by the volcanic eruption in Iceland may seem a long way from New Zealand, but a similar mass-grounding of aircraft could potentially occur here, volcanologists say.
New Zealand has plans in place for volcanic emergencies and state-of the-art monitoring of volcanoes, but a major eruption in the North Island could overwhelm large parts of the country, said Volcanology Section Manager at GNS Science, Gill Jolly.
The most serious scenario would be a major eruption in or near Lake Taupo or in the Okataina Volcanic Centre that includes Mount Tarawera in Bay of Plenty, Dr Jolly said.
“Taupo and Okataina have a history of large and violent eruptions, but they are often a thousand or more years apart. An eruption the size of the last one from Lake Taupo 1800 years ago could seriously impact at least 200,000 people in the centre of the North Island, but fortunately they don’t happen very often,” she said.
A more likely threat comes from the cone volcanoes in the Central North Island. Mt Ruapehu typically has small eruptions every dozen or so years and larger eruptions about twice a century.
“It’s definitely worth planning for this type of event because many people will experience it at least once in their lifetime.”
As most of the population lives some distance from New Zealand’s volcanoes, wind-blown volcanic ash will be the most likely hazard people face.
“This will happen if the wind blows the ash plume their way. Knowing how to deal with a coating of volcanic ash can save a lot of grief. There is good information available on this topic on science and emergency management web sites.”
Dr Jolly said people who could remember the 1995 and 1996 Ruapehu eruptions would know that even a modest eruption can cause major disruption in New Zealand.
The Ruapehu eruptions in the mid-90s threw out a total of 60 million cubic metres of acidic ash, blanketing areas up to 300km from the volcano.
“This was New Zealand’s first major eruption for many years and many valuable lessons were learnt. The systems we have in place now for monitoring volcanoes and for dealing with a volcanic crisis are significantly better than in the 1990s.”
At the peak of Ruapehu’s eruptions in the mid-1990s, ash plumes reached to 10 kilometres high and volcanic ash spread over large parts of the North Island.
Aviation authorities declared no-fly zones in the North Island and up to 11 airports were closed. The plans of thousands of airline passengers were disrupted. Ash also caused millions of dollars of damage to hydro-electric turbines and electricity transmission facilities in the central North Island.
Other impacts included damage to crops and closure of State Highway 1 on several occasions. Ash also caused livestock deaths in the Central Plateau, along with minor contamination of rivers and water supplies.
Graham Leonard, a volcanologist at GNS Science, said the global earth science community was watching events in Iceland closely and valuable information would be learned.
“Iceland is dealing with multiple disruptions to its infrastructure, economy, and daily life much the same as New Zealand would need to do if an eruption occurred here,” Dr Leonard said.
“This eruption has highlighted that ash fall of only a few millimetres thick can have a surprising range of impacts on infrastructure and transport facilities. Aside from respiratory impacts, fine ash particles can easily enter buildings and houses and cause havoc to electrical equipment and clog air conditioning.
“Cleanup and disposal of volcanic ash can be a huge undertaking and managing the use and distribution of water during this time is invariably a major challenge.”
Deciding when to put resources into cleaning up ash was difficult when eruptions could continue intermittently for weeks or months, Dr Leonard said.
“The potential for ongoing ash falls is a problem facing Iceland and parts of Europe right now. It’s a problem that is relevant to New Zealand, as drawn-out eruptions can potentially occur here.”
Dr Jolly said in the wake of the 1995-1996 Ruapehu eruptions, a number of New Zealand agencies combined to bring in a Volcanic Ash Advisory System. GNS Science contributes to this system by providing the Met Service with information on eruptive activity in New Zealand.
The ash advisory system assigns a colour code to volcanoes giving the aviation industry a quick indication of the ash hazard for aircraft.
GNS Science also monitors New Zealand volcanoes through its GeoNet project. This Earthquake Commission-funded project provides real-time monitoring of geological hazards in New Zealand for rapid response by emergency agencies, for public information, and for scientific research.
Dr Jolly said typically a volcano might give hours or days of warning signs before eruptive activity started. However, because volcanoes were complex, sometimes eruptions occurred without any warning signs.
Conversely, precursor signs might occur for days or weeks and then subside with no eruptive activity. This made the task of forecasting the next stages of volcanic unrest particularly difficult, especially as no two eruptions were the same.
Preparing during the ‘quiet times’ between eruptions gave the best chance of getting through a crisis event with minimum loss and disruption, Dr Jolly said.”