A once in a 1000-year eruption

On Saturday 15 January 2022, the Hunga volcano erupted sending a plume of ash and volcanic gas 30 kilometers into the atmosphere and generating tsunami waves across the Pacific. The full impact of this eruption is still being assessed, but the greatest devastation occurred on islands of Tonga. To get a better understanding of this event and its long term impact we speak with Professor Shane Cronin, a volcanologist from the University of Auckland, New Zealand.  

A conversation with Professor Shane Cronin

Can you please provide some background on the Hunga volcano and recent eruption events?

Image by Planet Labs PBC via AP
Hunga Tonga – Hunga Ha’apai Islands

The small Hunga Tonga – Hunga Ha’apai Islands are the tip of a much larger underwater volcano called the Hunga volcano, around 1,800m high and 20km wide. The Hunga volcano is part of a chain of volcanoes stretching from New Zealand to Samoa.

Over the past few weeks, the Hunga Volcano has erupted three times. The first two eruptions on the 20th of December 2021 and 13th of January 2022 were moderate in size. The third eruption on the 15 January 2022 was one of the largest eruptions seen in the region in modern history. This extraordinary eruption generated a 30km high plume of ash and gas, triggered a tsunami which travelled across the Pacific Ocean and radically changed the top of the volcano.

This volcano has erupted three times since late December 2021. What are the current observations over the last few days and future scenarios being considered?

Monitoring data from the past few days has not shown any signs of ongoing eruptions. However, the potential for further eruptions is a very real possibility. Current thinking suggests two main scenarios are possible:

First, the magma present during the 15 January 2022 eruption has been exhausted and the volcano will calm down.

Alternatively, new magma will enter the volcano and cause further eruptions. In this scenario the eruptions are unlikely to be as large as the 15 January 2022 eruption.

Therefore, it is important that people are aware of the possibility for further eruptions and monitor up-to-date information from relevant National Authorities.

Is there a risk of future tsunamis from the volcano?

Yes. There is potential for further tsunamis, particularly if future eruptions occur. It’s difficult to monitor as there isn’t seismic monitoring sites close to the volcano, but good information can come from local observations.  If new eruptions create sonic booms or shock waves through the air like the ones many people heard on the 15th January, it’s wise to go to higher ground, particularly for people located in areas impacted by the recent tsunami, and for the time being, this could be the best warning signal for tsunamis generated by the volcano.

Is there a reason why the tsunami wave didn’t trigger tsunami warnings and sirens across the world?

Current models for generating tsunami early warnings are based on earthquake events, whereas this tsunami was triggered by a volcanic eruption. The volcanic mechanisms which created this tsunami are complex and very different from an earthquake. Modellers are now working on new models to incorporate these complex processes. This is very much science in progress. In the meantime, anywhere that has experienced the 15th of January tsunami and associated booming noises and ocean behaviour and other natural warning signs, should pay attention to these natural signals with vigilance over the coming few weeks. 

What impact could this volcanic activity have at other locations across the Pacific? Is this expected to increase volcanic and seismic activity at other locations across the region?

A good question.  It’s commonly asked whether the eruption of one volcano can affect other volcanoes. The answer is almost certainly not, as each volcano erupts according to its own mechanism. Sometimes there are coincidences as we have thousands of volcanoes, but each volcano has its own plumbing system, including source and storage systems of magma, and operate under their own cycle. Volcanoes operate independently of each other.

There’s a lot of talk about plumes, ash, volcanic gas and acid rain – what are these? 

A volcanic plume consists of ash and gases.  Ash (or tephra) is broken up pieces of sharp, gritty rock, which are generally coarser close to the volcano, and further away can be fine grained and dusty.  Ash stays in the atmosphere for several days and gradually falls out.  The other part of a volcanic plume is gas, including sulphur dioxide, water vapour, carbon dioxide and other elements such as Chlorine and Fluorine, which float with the ash particles.  As the ash particles fall out, gases stay in the atmosphere.  The plume from the 15th of January eruption has dissipated from Tonga and Fiji and most of the ash has already fallen out, whereas the gas has blown towards Northern Australia up to a height of around 25km.  The problem is when gas and ash fall down and affect low lying areas.  Gas generally doesn’t fall by itself but can be rained out, along with ash or after ash.  Acid rain is generated when water droplets form within the plume react with the gases and fall to earth.

Can volcanic ash and acid rain impact food crops?

Ash and acid rain can have important impacts on food crops, but it’s not all bad news.  The main impact is not from toxins but from acidity, which can affect plants via both ash and acid rain.  Ash combined with fine rain can stick to leaves and burn them.  Green leafy crops may be badly affected, whereas root crops won’t be affected even if the leaves get burned.  Acid rain can be a problem for some plants when there is prolonged or repeated exposure and is more of an issue during fine rain than in heavy downpours where the acid is diluted.

What impact could this volcanic activity and tsunami have on marine life?

Near to the volcano or where there’s a large amount of ash entering water, there can be initial impacts on marine life. Instantaneous fish deaths can occur due to acidity and sharp small particles that can kill marine life.  However, marine life will recover and even bloom, because when ash falls on ocean it adds elements such as iron, which can stimulate plankton growth and kick start a recovery cycle or even a boom in marine life.  Further away from volcano there is much less likely to be any impact.  Toxins should not be an issue, and if fish are healthy, they should be safe to be consumed as usual.

What impacts could the volcanic ash have on rainwater tanks and groundwater supplies?  Should communities be concerned about the toxicity of drinking water affected by ash and acid rain?


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Volcanic Ash 

Groundwater is generally not affected by ash or acid rain, as soils are very good at filtering substances of concern.  Even shallow bores are very safe, and this has been well demonstrated in Vanuatu.  The main impact on harvested rainwater water associated with ash is the fine particles, which need to be allowed to settle and not stirred up. Affected rainwater won’t be poisonous to drink but may taste slightly metallic because of extra salts from ash and acid rain.  Despite the taste impacts, collected rainwater will be still safe to drink over the short term and shouldn’t be wasted unless there is an abundance of alternative supplies. 

Are there steps communities can take to minimise the impact of ash on drinking water supplies?

If communities know there is an ash fall starting to occur and have a roof-fed water supply, one of the ways to protect is to disconnect the pipe from tank while ash is falling.  Water in the tank will be safe if the tank is covered.  When the roof has been flushed with rain, the tank can be safely reconnected.

Can ash have an impact on the local power supplies needed to pump water?

For generators powered by diesel or other fuel, the biggest problem can be ash getting into the air filter.  If ash is blowing around constantly (such as from cars driving past), the air filter can get clogged up very quickly.  Solutions include operating the generator for shorter periods, sheltering the generator, cleaning air filters regularly, and in all cases not operating without an air filter.  Solar panels may need to be cleared of ash to work, which is usually best done by gently brushing off ash when it is dry.  Wet ash can be gently removed with water, taking care not to scratch the panels through scrubbing. 

In past volcanic events, Fluorine has been a substance of concern with respects to drinking water supplies, is that the case with the Hunga volcano?

Fluorine is often associated with volcanic eruptions.  It’s an element that is all around us in our environments, and an essential element that we all need.  It can be a problem if there is too much over a prolonged period, which can occur in locations where volcanoes are always erupting.  In the Tongan volcano, the composition of magma isn’t especially rich in Fluorine and this would be expected to be a low threat at the moment, particularly as we’ve only experienced one reasonably-sized eruption so far. For eruptions over days or weeks there should be no problem.

View the full interview below 


For access to more resources on how to respond to volcanic events please see useful links noted below:

Volcanic gases 
Health Impacts and Volcanic Gases
Information on different volcanic gases    

Volcanic ash
Health Impacts on volcanic ash
Protection from breathing ash
Guidelines for preparedness for ashfall
Volcanic ash impacts and information

Water information and volcanic events
Volcanic ashfall impacts on water supply

General Information on volcanoes
USGS Volcano Information

Full transcript of this interview available here


Professor Shane Cronin is a volcanologist at the University of Auckland, New Zealand who has extensive experience in the Pacific, including Fiji, Tonga, Solomon Islands and Vanuatu.

Professor Cronin’s speciality is volcanic hazards but has expertise and interest in seismic hazards and how people respond to them.



Blog Category
Geoscience, Energy and Maritime