Volcanic Unrest and How To Survive It

Over the next century, large magnitude volcano eruptions are many times more likely to happen than all risk of large asteroid or comet impacts combined.  The World is not prepared.

Volcanic Planet

Volcanoes erupt only at certain locations on Earth, and volcanic eruptions do not occur randomly.

The tectonic plates and shown in red the very active region around the Pacific ocean called the Ring of Fire.

The Earth’s crust is broken into a series of tectonic plates.

Although rigid, these plates float and drift very slowly on the hotter, softer layer of the Earth’s interior over very long periods of time.  As they move, they spread apart, collide, or slide past each other.

Around 60% of all active volcanoes occur at the boundaries between tectonic plates.

Ground Volcanoes

Volcanoes are monitored better than ever.  Indeed that is true for most known active land volcanoes, including webcam feeds, alert warnings and live statistics.

However, there are probably many other active volcanoes.  Their recent eruptions may as yet be unobserved due to their remoteness, or their having lain dormant for a really long time.

Submarine Vocanoes

The number of submarine volcanoes is estimated to be much higher, but are much more difficult to document than those on land because they are usually hidden beneath miles of ocean water.  And the deep sea remains largely unexplored.

Accordingly, most submarine eruptions go unnoticed.

Undersea volcanoes grow slowly upwards by recurring eruptions. When they reach the water surface, they become volcanic islands like Stromboli in the Mediterranean Sea.

The recent Hunga Tonga–Hunga Ha‘apai eruption has galvanised the scientific community and underscored the need for further exploration of this uncharted realm.

Identifying potentially active volcanoes requires a comprehensive approach.

How do scientists find out when and where in the World the next volcano will blow?

Active Volcanoes

According to USGS, there are potentially 1,350 active volcanoes on Earth.  Aside from the continuous volcanic belts on the ocean floor at spreading centres like the Mid-Atlantic Ridge, about 500 of those volcanoes have erupted in recorded history.

Many of those volcanoes border the Pacific Rim in what is known as the “Ring of Fire.”

There are 161 potentially active volcanoes in the United States and its territories.

Most of them are located in Alaska, Hawaii, California, Washington and Oregon.  Volcanoes in the Cascade Range and Alaska (Aleutian volcanic chain) are part of the Ring, while Hawaiian volcanoes form over a ‘hot spot’ near the center of the Ring.

Although most of the active volcanoes we see on land occur where plates collide, the greatest number of the Earth’s volcanoes are hidden from view, occurring on the ocean floor along spreading ridges.

Identify Risks

Further research into historical and geological records — including marine and lake cores, especially in neglected regions such as southeast Asia — would help to pinpoint volcanic hazards and map out where large eruptions tend to happen.

Map with active volcanoes and larger cities, modified after U.S.G.S. 2005.D.Bressan Source: Forbes (2021)

Regions of heightened vulnerability and exposure to volcanic threats should be identified.

More than 800 million people are living within 100 kilometres of an active volcano.

That will require interdisciplinary research to locate the highest global risks to trade, energy, critical infrastructure, food and water security, and finance.

There are likely to be pinch points where large volcanic threats overlie dense trade networks, for example the Straits of Malacca — between Peninsular Malaysia and Sumatra in Indonesia — and Mediterranean Sea.

Examine Ice Records

A piece of ice from Antarctica showing the tiny air bubbles it contains. Image:Wikipedia/CSIRO

The properties of ice and the material trapped inside of it can be used to reconstruct the ancient climate over the age range of the core.

The air trapped in tiny bubbles can be analysed to determine the level of atmospheric gases such as hydrogen, oxygen, and greenhouse gases like carbon dioxide (CO2).

Measuring the proportions of oxygen and hydrogen isotopes provide climate scientists with information about temperature variations.

Ancient volcanic events that were sufficiently powerful to send material around the globe have left a signature in many different ice cores.

This ice core from Antarctica shows a very thick layer of volcanic ash.  Source: Oregon State University/DiscoverMagazine

Ice core records tell us of 97 large magnitude eruptions, although only a few could be attributed to specific volcanoes.  Others remain mysterious despite occurring more recently, like the volcanic eruptions that led to the ‘Late Antique Little Ice Age’ in the mid-6th century.

Over the last 10,000 years, 1,300 volcanoes have erupted.  Those volcanoes are considered active.


More has to be done to forecast and manage the effects of
globally disruptive volcanic eruptions.

The risks are much more devastating than people imagine.

The Case of the Hunga Tonga–Hunga Ha‘apai Volcano

A sliding GIF of two satellite images shows the Hunga Tonga-Hunga Ha'apai volcano before and after the eruption. Image: MAXAR/Getty
Before and after the Hunga Tonga–Hunga Ha‘apai volcanic eruption on 15 January 2022. Source: MAXAR/Getty

The massive eruption of the Hunga Tonga–Hunga Ha‘apai volcano in Tonga, South Pacific Ocean, was the volcanic equivalent of a near-miss large asteroid whizzing past the Earth.

The January 2022 eruption was the largest since Mount Pinatubo, Philippines, blew in 1991.  Only the Krakatoa eruption of 1883 rivalled the atmospheric disturbance produced.

The eruption obliterated a volcanic island north of the Tongan capital Nuku’alofa.

The explosion was heard thousands of kilometres away.  It was the biggest ever recorded by modern instrumentation.  NASA determined that the eruption was equivalent to between 4 to 18 megatons of TNT – hundreds of times more powerful than the atomic bomb dropped on Hiroshima.

The plume of ash rising from the Hunga Tonga–Hunga Ha‘apai eruption photographed by Himawari-8 satellite. Source: JMA

The eruption column ejected a large amount of volcanic material into the stratosphere. – an estimated 400,000 tonnes of sulfur dioxide (SO2).

Ash fell over hundreds of kilometres, polluting the water supplies, affecting the infrastructure, agriculture and fish stocks.

The damage amounted to 18.5% of Tonga’s GDP (gross domestic product).

The most recent Hunga Tonga-Hunga Ha’apai volcano eruption created a shockwave registered by the GOES-17 NOAA satellite.

The volcanic blast created worldwide atmospheric shock waves that propagated around the globe, and tsunamis that reached Japanese and North and South American coastlines.  Remote sensors recorded the shock waves reverberating for days.

Submarine cables were severed, cutting off Tonga’s communications with the outside world for several days.

The eruption lasted about 11 hours.

The Hunga Tonga-Hunga Ha’apai eruption on Jan. 15, 2022, caused many effects that were felt around the world and even into space. Some of those effects, like extreme winds and unusual electric currents were picked up by NASA’s ICON mission and ESA’s Swarm.

If the Tonga eruption had gone on longer, releasing more ash and gas into the atmosphere, or if it had occurred in a more densely populated area, near a high concentration of vital shipping lanes, electricity grids or other crucial global infrastructure, the repercussions on supply chains, climate and food resources worldwide would have been enormous.


The Tonga eruption must be a wake-up call.


Planetary Defence

Although the climatic impacts of large asteroid events and volcanic eruptions are comparable, the response is vastly different.

‘Planetary defence’ receives hundreds of millions of dollars in funding each year, and has several global agencies devoted to it:

DART and Planetary Defence

NASA’s DART mission is a planetary defense driven test of technologies and will be the first demonstration of a technique to change the motion of an asteroid in space.

The destination of this mission is the small asteroid Dimorphos – a moonlet – which orbits slowly around its larger companion Didymos.

This September, NASA’s Double Asteroid Redirection Test (DART) mission will try to nudge an asteroid’s trajectory, testing capabilities for future asteroid deflection.

Launched from Earth in November 2021, the mission will deliberately crash a space probe into the minor-planet moon Dimorphos of the double asteroid Didymos to assess the future potential of a spacecraft impact to deflect an asteroid on a collision course with Earth through a transference of momentum.

The DART spacecraft will achieve the kinetic impact deflection by crashing into the moonlet.  The collision will change the speed of the moonlet in its orbit around the main body by a fraction of 1%, but this will change the orbital period of the moonlet by several minutes, long enough to be observed and measured using telescopes on Earth.

That advance-preparation project will cost over US$300 million.

By contrast, there is no coordinated action, nor large-scale investment, to mitigate the global effects of large-magnitude eruptions.  This has to change.

Supervolcanoes and Supereruptions

Comparison of volumes of magma erupted from selected volcanoes within the last 2 million years. Source: USGS

A supervolcano is defined as a volcano that has had at least one explosion of magnitude 8, the highest ranking on the Volcanic Explosivity Index (VEI).

This means a volcano that has released more than 1,000 km3 (cubic kilometers) of magma during an eruption.

Magnitude 7 Volcanic Eruptions

The Samalas volcano eruption of 1257 had a probable VEI of 7.  It is now considered the likely source of high concentrations of sulfur found in widely dispersed ice core samples.  It may have been the most powerful volcanic blast since humans learned to write.

The most powerful eruption in modern times was the VEI 7 eruption of the Tambora about 200 years ago.

Tambora Eruption, 1815

The caldera at Mount Tambora Image: HeadStuff

The last magnitude 7 event was in Tambora, Indonesia, in 1815.

The eruption had 4–10 times the energy of Krakatoa eruption (1883).  An estimated 100 km3 of pyroclastic material was ejected, weighing approximately 1.4×1014 kg.

Although estimates vary, the death toll was over 71,000 people.  In the archipelago, people died as a result of the volcanic flows, tsunamis, deposition of heavy rocks and pumice ash on crops and houses, and their subsequent effects.

Globally, temperatures dropped about 1 °C on average.

It was the ‘year without summer’.

Eastern United States and Europe endured mass crop failures, and the resulting famines led to violent uprisings and disease epidemics.

Indonesia’s population has expanded rapidly since the 1815 Tambora eruption.  The population reached 238 million people in 2010, of which 57.5% are concentrated on the island of Java.  A volcanic event of the same magnitude would potentially impact about 8 million people.

Recent data from ice cores suggest that the probability of an eruption with a magnitude of 7 or greater, that is 10-100 times larger than Tonga, this century is 1 in 6.

And yet, little investment has gone into mitigating the effects an eruption of this magnitude could have.

The impact would cascade across much of our infrastructure (transport, food, water, trade, energy, finance) and communications networks.

In the past, eruptions of this magnitude caused abrupt climate change, the collapse of civilizations, and even the rise of pandemics.

The eruption of Hunga Tonga was more explosive than a super volcano, but instead of blowing apart, the volcano remained intact, prompting volcanologists to reassess their theories about what mechanism might have caused such violence.

Even more puzzling is the fact that Hunga Tonga’s energy dispersed in a sheer vertical pattern rather than outward across the seafloor.

The waves didn’t follow the traditional pattern of decay.  They seemed to hold more energy and create a wave that was well recorded, even as far as the Ross Ice Shelf in Antarctica.

Mike Williams

Chief Scientist of Oceans, NIWA

Eruption Frequency

Global volcanic eruption history over the last 80 ka, based on data in the LaMEVE database, and ice volume conditions.: (a) Number of Magnitude ≥6 (Pinatubo-sized or larger) NH and SH eruptions per two millennia from present to 80 ka BP. The low number of known SH volcanic eruptions prior to the last two ka reflects a significant undercount in known eruptions. (b) Latitude and ages of known Magnitude ≥6 volcanic eruptions from present to 80 ka BP36. (c) A histogram of abrupt Greenland warming events37, the Red Sea sea level reconstruction (interpreted as reflecting global ice volume)38 (solid black line), and 65°N insolation35(dashed blue line). Intervals characterised by high ice volume and low insolation hypothesised as relatively insensitive to SH eruptions are highlighted in blue; intervals with very low ice volume lacking the positive feedback required to sufficiently amplify volcanic eruptions are highlighted in orange. Source: ResearchGate

Researchers have long known of the drastic impacts of large-scale volcanic eruptions, but the likelihood of such an event has only recently been clarified.

The frequency of large eruptions can be determined by searching long-term records for sulfate spikes, stemming from the gas released during globally significant events.

The mechanisms responsible for millennial scale climate change within glacial time intervals are equivocal.

In 2015, scientists showed that all eight known radiometrically-dated Tambora-sized or larger Northern Hemisphere eruptions over the interval 30 to 80 ka BP are associated with abrupt Greenland cooling with over 95% confidence.

In 2021, researchers looked at ice cores from both poles and identified 1,113 signatures of eruptions in the Greenland ice and 737 in Antarctica, occurring between 60,000 and 9,000 years ago.

They found 97 events that probably had a climatic impact equivalent to that of a magnitude 7 eruption or greater.

They concluded that magnitude-7 events happen about once every 625 years, and that magnitude-8 events (or super-eruptions) happen about once every 14,300 years.

This estimate is lower than the time-scales suggested by other assessments, using geological records and statistical techniques, that found recurrence intervals of 1,200 years for magnitude 7 and 17,000 years for magnitude 8.

The recurrence rate of large eruptions could also increase as geophysical forces on the planet’s surface shift because of:-

    • ice melt,
    • changes in precipitation and
    • sea-level rise.

Global Cooling: Economy and Population Decline

While ongoing changes in ocean currents and atmospheric circulation patterns have caused global warming, a large magnitude eruption in the Tropics could cause 60% more cooling over the next century compared with today.

Particles in Upper Atmosphere Slow Down Global Warming Diagram: NASA

Although the cooling effects of sulfate aerosols (SO2) in the stratosphere might counteract global warming from greenhouse gases, the impact of a large volcanic eruption would be phenomenal, with uneven effects on weather, rainfall and temperature.

The global population is 8 times larger now than in 1800, and the trade it relies on has also grown more than 1,000-fold since then.

The modern world is highly dependent on global trade for food, fuel and resources.

As our World knows only too well, a disaster in one place can cause price spikes and shortages far away.


The financial losses resulting from a large-magnitude eruption are estimated to be in the multi-trillions, roughly comparable to those of the COVID pandemic.

Given the estimated recurrence rate for a magnitude-7 event, this would equal to more than US$ 1 billion per year.

Earth scientists call for increased attention to, and coordination in, research aimed at forecasting, preparedness and mitigation of large-scale volcanic eruptions.  Obviously, sound investment in disaster preparedness and mitigation is cheaper than reacting to a full-blown crisis.

What must we do?

Improve Ground Monitoring

Since the 1950s, only 27% of eruptions have been monitored with at least one instrument such as a seismometer.

Data from only about 1/3 of these eruptions have been collected by the global volcano unrest database aimed at improving eruption forecasts, WOVOdat.

Improved ground-based monitoring of known active volcanoes, along with seismicity measures, gas release and ground deformation, could help delivering better advance warning of eruptions, especially in combination with artificial intelligence (AI).

Estimates indicate that up to 80% of magnitude-6 eruptions (or greater) from the start of the Holocene until about 1 A.D. are currently missing from the global geological record, with especially poor data for oceanic islands such as the Kuriles, as well as Indonesia and the Philippines, countries with some of the highest densities of volcanoes.

Optimise Satellite Observation

Where local ground-based monitoring is not feasible, particularly in remote areas, satellite and aerial observation become essential.

The Hunga Tonga-Hunga Ha’apai volcano eruption was recorded on 15 January 2022 by GOES-17 Satellite, NOAA

In addition to monitoring thermal, gas and deformation changes, satellites could provide real-time mass eruption rates, plume heights and imagery for disaster relief.

But current satellites lack the necessary resolution in time and space.

After the Tonga eruption, it was 12 hours before the first radar images, from the European Union’s Sentinel-1A probe, captured changes at the volcano.

Often, volcanologists must also rely upon the generosity of private satellite companies to provide real-time high-resolution imagery, as was the case when Capella Space, based in San Francisco, California, provided images one day after the explosive eruption of La Soufrière, in Saint Vincent and the Grenadines, began in April 2021.

Committee on Earth Observation Satellites (CEOS)

A four-year pilot project by the Committee on Earth Observation Satellites (CEOS) showed that existing satellite-radar images of ground deformation could be harnessed to help to track volcanic activity in Latin America.

CEOS recommended a host of steps to:-

For over two decades, volcanologists have called for an orbital volcano observatory satellite to be launched.

Much progress has been achieved by sharing satellites.

However, a step-change in volcano surveillance could be achieved with a dedicated satellite observing in the infrared, or high-altitude drones that act as pseudo-satellites for months at a time.

Prepare Communities

To increase resilience at the community level and support the humanitarian responses, real-time monitoring and simulations of ash fallout, gas plumes and other hazards, such as volcanic flows, should be fed into real-time, targeted communication.

This nowcasting could be delivered by SMS, providing vital real time advice to the locals or pointing them to the nearest centres for emergency supplies and healthcare.

Increased emphasis on community-focused education and awareness can help prepare people in vulnerable regions.

The Volcano Ready Communities Project in Saint Vincent and the Grenadines, run by the University of the West Indies Seismic Research Centre, is a success story.

It contributed to the effective evacuation of 20,000 people before the 2021 explosive eruptions, with no loss of life.

Similar community-awareness programmes should be scaled up around the globe.

Build Resilient Infrastructures

Building greater resilience into critical infrastructure, such as energy grids and communications networks, could lessen regional impacts.

Global policy agreements ought to prioritize the transport of important commodities, such as:-

    • oil,
    • gas,
    • fertilizers,
    • food,
    • electronics and
    • crucial metal resources.

Those should also ensure that countries do not act in their own narrow interest, e.g. instigating export bans that could exacerbate food shortages.

Global bodies such as the United Nations Office for Disaster Risk Reduction have not yet undertaken such efforts.

Geo-Engineer Volcanoes?

With increasingly sophisticated methods of detection, volcanologists hope to:-

    • improve early warning systems,
    • determine environmental impact,
    • mitigate hazards posed by eruptions, and
    • aid in ecosystem recovery.

Who are the people trying to find where the next underwater volcano is hiding?  And where do they look next?

Sound speed as a function of Depth, taken at a position north of Hawaii in the Pacific Ocean. The SOFAR channel axis is at around 750-metre depth. Source: Wikipedia/World Ocean Atlas

Hydroacoustic monitoring is a helpful technique.

At depths of 1,000 m, temperature, pressure and salinity all slow the movement of sound, facilitating the transmission – a zone known as the Sound Fixing and Ranging (SOFAR) channel.

When a volcano erupts under water and the lava flow interacts with freezing water, it vaporises producing an array of sounds, from sharp cracks and booms to slow rumbles.


Deep volcanoes do not pose much danger.  More dangerous are those near the sea surface or that emerge above it.

Javier Escartin

Laboratoire de Géologie, ENS, Paris

NIWA (National Institute of Water and Atmospheric Research)‘s mission is to conduct leading environmental science to enable the sustainable management of natural resources for New Zealand and the planet.

Remote-controlled glider probe deployed by the NIWA Tangaroa mission. Image: NIWA/NipponFoundation/TESMaP/Parsons-King

Researchers aboard the Tangaroa vessel deployed remotely operated instrumentation to record video footage and physically sample the outer caldera of Hunga Tonga-Hunga Ha’apai.

Given that the Pacific region is so seismically active, NIWA scientists were in a unique position to investigate the caldera’s dramatic impact.  They surveyed thousands of square kilometres of the seafloor as part of the Tonga Eruption Seabed Mapping Project.

Submarine volcanoes often fall under their own weight.  When sea water mixes with boiling hot lava, this can lead to an explosive collapse.

Again, some of the most widespread impacts of large-magnitude eruptions arise from the massive stratospheric injection of sulfur aerosols that can block sunlight and abruptly cool the Earth.

Research into how to counteract them could help curtail a  volcanic winter.

Studies have considered the use of sulfates to counteract human-induced warming by deflecting solar radiation.

The opposite scenario rarely gets attention.

Theoretically, it is possible to release a short-lived greenhouse gas, such as a hydrofluorocarbons (HFCs) – man-made organic compounds that contain fluorine and hydrogen atoms – to counteract the cooling of sulfates, or to use a high-altitude aircraft to release non-toxic chemical substances that bind to sulfate aerosols to enhance their removal from the atmosphere, in a manner similar to cirrus cloud thinning.

Such efforts might have significant costs and side effects, such as acid rain, as well as large potential benefits.

Being able to affect volcanic behaviour directly might seem inconceivable.  But then, so did the deflection of problematic large asteroids until the formation of NASA’s Planetary Defense Coordination Office in 2016.

Numerous examples from geothermal exploration show that it is technically possible to penetrate magmatic bodies in the crust with little collateral damage.

Krafla Magma Testbed, Iceland

A diagram showing the drilling progress at the Krafla caldera in Iceland. Diagram: Abigail Malate
Iceland Deep Drilling Project’s well at Krafla. Source: Inside Science/Malate/American Institute of Physics

In 2024, researchers plan to drill into a magma pocket at the Krafla test bed in Iceland, to provide a ‘long-term magma observatory’ and test sensing equipment to potentially improve volcanic prediction.

The Krafla caldera is seated on the Iceland hotspot atop the Mid-Atlantic Ridge, which forms the divergent boundary between the North American and the Eurasian Tectonic Plates.

There have been 29 reported eruptions at this location

Since 1977, the Krafla area has been the source of geothermal energy used by a 60 MW power station.

A survey undertaken in 2006 indicated very high temperatures at depths of between 3 and 5 kilometres.

These favourable conditions led to the development of the first well from the Iceland Deep Drilling Project (IDDP) that found magma 2.1 km deep beneath the surface, making Krafla the only place on Earth where we know exactly where magma is below our feet.

The Krafla Magma Testbed (KFM) is bringing a closer understanding of magma to the World.

Research should also be undertaken to assess if it is possible to manipulate the magma or surrounding rocks to moderate eruption explosivity — one such project, Magma Outgassing During Eruptions and Geothermal Exploration, has funding from the European Research Council to 2026.

Whether scientists should conduct any volcano engineering, which has risks, is a matter for debate.  But such a debate requires rigorous theoretical and experimental research to underpin it.

The lack of investment, planning and resources to respond to large eruptions seems reckless.

Will humanity learn from volcanology’s near miss in Tonga?  Or will a supereruption be the next global event to catch us unprepared?

Our World is different now.  We are better educated and aware. Humanity lives longer, healthier and safer lives than ever.

Yet the risks to humanity are increasing…

Hunga Tonga erupted out of type, and that’s what’s confused us: this volcano didn’t behave the way textbooks say it should.

Kevin Mackay

Marine Geologist, NIWA

Scientists are calling for more urgent action.