On the 15 January 2022, the partially submerged Hunga Tonga-Hunga Ha’apai volcano (~<200 metres underwater) erupted explosively, sending a shockwave that lapped the Earth multiple times. It had been erupting since December 2021, but had so far passed with little to no concern. However, the power of the eruption on the 15 January was something we have not witnessed in 21st Century, certainly not with our global earth observations like satellites, which witnessed the resulting shockwaves crossing the Earth, and measured a volcanic ash plume over 30 km high (55 km high max into the mesosphere) spreading over 650 km in just one hour. The explosion itself was equivalent to a 4 -18 megatons of TNT. In an eruption lasting just hours long (perhaps ~6, but sustained and most intense part was ~3 hours long, with initial blast potentially much shorter) the impacts from this eruption were significant:

Initial impacts

  • Accompanying the eruption a tsunami struck Tonga and the South Pacific, washing away all the houses from islands 70 km away- about 5 people died as far as we know, but 100’s houses have been destroyed damaged or are unliveable
  • The tsunami also affected coasts 1000’s km away in multiple nations, in two different oceans, with two people dying in Peru.
  • Ash fall (a few cm thick) covered a huge area of a Tonga, with the majority of the population (approx. 105,000 people) impacted.
  • Power and communications to the whole of Tonga was cut off when the submarine Tonga Cable was severed by submarine gravity flows from the collapse of the Hunga Tonga Hunga Ha’apai islands.
  • It estimated that about 60 – 70 percent of livestock-rearing households either had livestock perished, experienced damage to grazing land, or have contaminated water supplies.

These have led to wide ranging and sometimes unexpected cascading impacts:

  • The tsunami caused an oil tanker to crash, creating a huge oil leak in Peru, causing widespread ecological damage.
  • Sanitation, sewage and drinking water (e.g. groundwater) are affected in Tonga from seawater and ash infiltration, with 50,000 people affected from lack of drinking water.
  • Vulnerable people will suffer from respiratory ill health from ash inhalation which may strain healthcare.
  • Delays to aid provisions as planes could not land, or fly due to lots of ash in the atmosphere and on the runways.
  • Internet, phone signal and communications will not be fully restored for 4 weeks following the eruption, until a ship comes to replace the submarine cable.
  • Some initial signs that the stratospheric ozone has been slightly depleted
  • Ash fall considerably damaged crops. The agricultural sector contributed nearly 14% of Tonga’s GDP in 2015-16 and represented over 65% of exports, so the country will be relying on aid for some time.
  • Tonga has recorded its first cases of Covid-19 from those dealing with aid in the ports forcing Tonga to go into lockdown for the first time (despite contactless aid protocols to avoid this).
  • Main risk going forward is the increased risk of infectious diseases because of sewage disruption, water contamination and shortage.

Despite these impacts, the death toll has so far been low, and the worst impacts have been mainly confined to 100s km from eruptions, that being said the impacts on Tonga from this short eruption will be felt for months or longer. But its ferocity for just several hours provides a glimpse into the impacts a much larger eruption could have. On the volcano magnitude scale (which measures the mass of magma erupted – Magnitude = log10(mass in kg) - 7), this eruption ranks fairly low (estimates so far are Mag 5), together with its erupted sulfur gas content (0.4 Tg). Yet its intensity (explosivity/power of the eruption), was at the higher end of the spectrum (erupting at an estimated rate of ~2 x108 kg/s). Meaning that if the eruption was sustained at this intensity for 5-6 days it would be a magnitude 7, or 50-60 days we would be seeing something on the order of a magnitude 8 eruption (super-eruption). Hence this unusually explosive, but short eruption provides something of a ‘preview’ into a large magnitude volcanic eruption (more on that here). 


So what can we learn from this? Firstly, is that we are far from prepared for such an eruption. Despite the volcano having explosive eruptions from December 2021, we had no forewarning that the volcano would produce an eruption of this intensity. The volcano had no monitoring equipment (the nearest seismometer is reportedly in Fiji), and we are especially ill equipped for monitoring submarine volcanoes, meaning that it was difficult to forecast, but also tricky to understand how long the eruption lasted. Satellites required to assess activity using radar imagery, or quantify the amount of sulfur erupted required waiting sometimes 10s of hours for satellite overpasses or persuading satellite companies to shift their orbits. There was also no tsunami alerts and no emergency plans in place for such a large eruption.

The second thing we can learn is that its remote location dramatically minimised its impacts, this occurred at an uninhabited island - 65 km from the nearest populations, and away from critical global infrastructure drastically. Tonga will be able to recover from such eruption, the magnitude of which occurs every 10-15 years somewhere on Earth. If this eruption happened in a more populated or infrastructure-rich region like the Mediterranean, or South East Asia, the initial and cascading impacts may have disastrous, both regionally and globally. Aside from location, some other circumstances prevented this from being a much bigger disaster on Tonga:

  • The eruption occurred with loud bangs (not always the case) - thereby providing some warning for a tsunami to evacuate from the coasts
  • It occurred in the afternoon- not at night making evacuations easier (though this also meant we lost some eyes on the volcano for a while with some observation satellites not able to image at night)
  • The tsunami was fairly small in the proximal regions (1-2 metres, unlike the Anak Krakatau volcanic tsunami in 2018)
  • Despite its size, the sulfur aerosol content was quite comparably low; it is possible the seawater scrubbed some of the sulfur from the eruption.
  • Knowledge and preparedness from the Tonga Red Cross and other authorities saved lives e.g. advice to cover drinking water to prevent it from ash contamination.
  • Ash fall was not heavy/thick enough to collapse roofs and rain did not arrive (which can exasperate this and trigger mudflows)
  • Ash was not heavy enough to destroy infrastructure (like transport network, healthcare centres), or make land redundant for living and growing on for years.
  • The eruption stopped quickly, allowing ash to settle out of the atmosphere and allowing planes to fly, this allowed surveillance and aid missions to arrive by plane & ships and other vessels can bring water and desalination equipment, as well as food aid etc.
  • The main airport was cleared of ash by locals allowing aid planes to land within days of the eruption
  • Internet satellite telecoms was provided 5 days later, albeit patchy 2G connectivity

The most important factor preventing a catastrophe was the duration (and therefore the mass of material erupted), a larger magnitude eruption would have global impacts, mostly from sulfur aerosol related impacts on the climate and related food shortages in this instance, since it did not occur in a particularly vulnerable regions (low population, limited infrastructure). 


How can we better prepare or understand these risks? These are some of the steps Lara and I are considering going forward in the next few decades of volcano research:

Identifying the risks

  • Identify the volcanoes capable of large magnitude eruptions (important volcanoes), are they neglected (i.e. not prepared for such eruption) and can tractable measures such as monitoring and infrastructure resilience be implemented? (Anecdotally we know of several volcanoes with >10s of millions living within 100 km with limited monitoring and preparedness).
  • Which regions in the world would be most affected by even modest eruption, with cascading global impacts (infrastructure, finance etc) can we use this information to build resilience (e.g. build more superconductor factories away from volcanic regions).
  • What regions in the world will be most affected by climate, food and water related affects, what are the worst-case scenarios/most affected regions? Which areas in the world will remain relatively unaffected, and therefore provide a source of food and resources. How can we use that information to inform food planning for disasters with resilience foods (with ALLFED’s knowledge/modelling)

By identifying the risks above, we hope to lobby NGOs and governments to invest in monitoring and preparedness in specific volcanically active and vulnerable regions. 

Building resilience

  • Investigate the role of pseudo-satellites (HALE UAVs) to help provide imagery and monitor most dangerous volcanoes when they start showing activity. These will also be critical post eruption to understand if the volcano is still erupting, how big the eruption is, the damage surveillance, and a source of internet and communications. Talk of this at Tonga with Starlink was discussed, but more formal arrangements/protocols ahead of time would be more effective.
  • Investigating the role technology could play in disaster response. Can we provide up to date advice on people’s phones for people and authorities in regions far away from eruptions with tailored advice in real time (so called ‘now casting’) (e.g. clear roofs to prevent collapse as ash will exceed 25 mm in this location, protect water and food supplies from ash, wear masks).
  • Enhancing community-led resilience mechanism. Can we apply citizen science to increase our monitoring and surveillance of the most risky volcanoes? How can we enhance education and outreach with communities to reduce the potential loss of life and build longer-term resilience?

Mitigating the risk 

  • For the stratospheric aerosols, can we research ways to minimise this, via coagulation and fallout of sun blocking sulfate aerosols using aircraft, balloons and UAVs. There is lots of research going into aerosol management for anthropogenic climate change, but nothing (that we know of) going into removal of aerosols in the event of large explosive eruptions/nuclear blasts/asteroid impacts.
  • How possible, effective and ethical is it to attempt to minimise the explosivity of eruptions before they erupt by fracking, drilling and other means.


For us these are the most tractable ways of mitigating the worst effects from catastrophic volcanic eruptions, which we are just starting to explore. If you’d like to know more about this or help us in any way we’ll be giving lightning talks at Centre for the Study of Existential Risk conference in April on these topics, or otherwise get in touch - it’d be great to chat. 


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