Tongariro: What will happen next? The three main scenarios

What will happen next after the midnight eruption at Tongariro?

"A steam-driven eruption like this could be a sign there is magma moving into place under the volcano, and we might see a progression through to a magmatic eruption," warns Dr Thomas Wilson, lecturer in hazards and disaster management at Canterbury University.

"Or it could just be the volcanic hydrothermal system has been unsettled by these earthquakes and we're seeing an eruption as a result of this?"

What's going to happen next? Dr Wilson says GNS scientists will know a lot more after collecting samples.

However, he says there are three main scenarios: 

• It could stop completely.
• It could continue with these same-size eruptions and we might get some more very light ash fall across the North Island, depending on the wind conditions.
• It could be the beginning of a bigger sequence, which would probably mean larger eruptions with more ash produced, probably leading to more widespread and thicker deposits. 

"I can't give you any probabilities on the likelihood of these scenarios. We do know that there have been eruptions from this part of the volcano in the past, and these have typically been pretty small on a global scale.

"But we can't rule anything out at this stage," Dr Wilson says.

A Tongariro ash cloud could hit Auckland
The ash cloud from the midnight Tongariro eruption might be heading east.

But an Auckland University academic warns there could be more activity from the mountain – and if so, a plume could head north to our largest city.

"It will be interesting to see how the eruption develops. Whether it continues for months or is over already," Dr Jan Lindsay, senior lecturer and vulcanologist at Auckland University, says.

"If the former we may see ash reaching Auckland, depending on the wind direction.

"We know from looking at sediment cores from Auckland lakes that ash from Tongariro has reached Auckland many times over the last 80,000 years," she says.

"It only needs to be in the atmosphere to cause a problem: we are already seeing flights cancelled and the impact on flights in and out of Auckland airport could be significant."