The August 1883 eruption of Krakatoa was one of the deadliest volcanic explosions in modern history. The volcano, found in the middle of the Sunda Strait in between two of Indonesia’s largest islands, was on a small island which disappeared almost overnight. The eruption was so loud it could be heard in Reunion, some 3,000 miles away.
As the volcano collapsed into the sea, it generated a tsunami 37m high – tall enough to submerge a six-storey building. And as the wave raced along the shoreline of the Sunda Strait, it destroyed 300 towns and villages, and killed more than 36,000 people.
Nearly 45 years later, in 1927, a series of sporadic underwater eruptions meant part of the original volcano once again emerged above the sea, forming a new island named Anak Krakatoa, which means “Child of Krakatoa”. In December 2018, during another small eruption, one of Anak Krakatoa’s flanks collapsed into the ocean and the region’s shorelines were once again hit by a major tsunami. This time, 437 were left dead, nearly 32,000 were injured and more than 16,000 people were displaced.
Even though Anak Krakatoa had been active since June that year, local residents received no warning that a huge wave was about to hit. This is because Indonesia’s early warning system is based on ocean buoys that detect tsunamis induced by submarine earthquakes, such as those that struck on Boxing Day in 2004, in one of the most deadly natural disasters of all time.
But tsunamis caused by volcanic eruptions are rather different and, as they aren’t very common, scientists still don’t fully understand them. And Indonesia has no advanced early warning system in place for volcano-generated tsunamis.
At some point in the future, Anak Krakatoa will erupt again, generating more tsunamis. Since it is difficult to predict exactly which areas of the Sunda Strait will be affected, it is of paramount importance that residents in coastal villages are well aware of the danger.
An advanced early warning system could be installed. It would involve tide gauges to detect an increase in water levels, satellite imagery and drone mapping, and a tsunami numerical model run in real time. When this system triggered a warning, it would be fed direct to residents who live in the coastal belt. Until such a system is in place, it will be vital to get the local community involved in disaster risk management and education.
We need to tell people about the risks
But preparing for future disasters isn’t just about building breakwaters or seawalls, though these defensive structures are clearly vital for preserving beaches for tourism and local businesses like fishing. It is also about educating people so that they feel psychologically healthier, more resilient and less anxious about facing the mega tsunamis of the future.
I have previously highlighted two examples of proactive community participation in disaster-prone villages in the UK and Japan. In both cases, residents know how to act in case of a natural disaster without depending on the authorities. It is certain that the decimation of the land and deaths could be reduced if the local communities are well prepared for natural disasters like tsunamis.
Following the December 2018 Anak Krakatoa tsunami, local researchers and I conducted a detailed field survey of the coastline of Lampung province, on the north side of the strait, and some of the smaller nearby islands. We found a lack of proper tsunami defence structures or any early warning system, and houses and businesses built very close to the coast with no buffer zone. We identified high ground where residents could run to in case of a tsunami and put up signs with evacuation routes.
During this survey, I conducted a series of focus group meetings with local residents and businesses in order to make the communities more resilient and reduce their anxiety about future mega tsunamis in the area. I developed a tsunami wave propagation model to replicate the 2018 tsunami and most plausible future tsunami events, and to identify the most vulnerable coastal stretches, such as the village of Kunjir on the Lampung mainland.
I also combined field survey results, numerical model outputs and published information to make some recommendations for local communities. I suggested active collaboration between government departments and local institutions on the issue, and the formation of disaster preparedness teams for every village in Southern Lampung. The planning criteria for development of infrastructure along the coasts should also be put under review, and there should be a trauma healing programme for the victims of the 2018 Krakatoa tsunami.
We don’t know exactly when Krakatoa will next erupt, or if any future eruptions will match those of 1883 or even 2018. That’s a question for volcanologists. But we should do what we can to prepare for the worst.
Stretching towards Antarctica lies a hidden natural oasis – a massive underwater plateau created when continents split more than 100 million years ago.
Straddling the Indian and Southern Oceans, the Kerguelen Plateau is three times the size of Japan. It’s farthest depths are four kilometres below the surface; its islands form one of the most isolated archipelagos on Earth. These include Heard Island and McDonald islands, Australia’s only active surface volcanoes.
Australia and France share a territorial border across the Kerguelen Plateau and work together to study it. The most recent findings, The Kerguelen Plateau: Marine Ecosystems and Fisheries, have been published by the Australian Antarctic Division.
The collaboration has fostered new knowledge of the Kerguelen Plateau as a unique living laboratory – and as the home to one of the world’s most expensive fish.
Tracking the Patagonian toothfish
Volcanic activity pumps vast amounts of minerals such as iron into the water, making the Kerguelen Plateau a biological hotspot.
The plateau hosts populations of Patagonian toothfish, or Dissostichus eleginoides, a predatory fish that lives and feeds near the bottom of the Southern Ocean. The brownish-grey fish grow up to 2 metres long, live for 60 years and can weigh 200kg. The species is often marketed as Chilean seabass.
Australia and France have worked together since the early 2000s to eliminate illegal, unregulated and unreported fishing, to understand the toothfish’s population dynamics and surrounding ecology. As a long-lived top predator with a broad diet, they have a key role in the structure of communities inhabiting the seafloor.
The toothfish is also economically important. Its snow-white flesh is prized as rich, good at carrying flavour and rich in omega-3 fatty acids. Catches command high market prices: prepared fillets have sold for more than A$100 per kg in recent years.
Approved commercial fishing vessels catch Patagonian toothfish around the plateau. Over the past few decades, scientific observers on fishing boats have tagged and released more than 50,000 toothfish at the Australian islands. This, along with annual surveys, biological sampling and data collection, has shed light on the species’ biology and population ecology.
This informs management measures such as total allowable catches and “move on” rules, where vessels must cease fishing in an area once a predetermined weight of non-target fish has been caught.
The nations continue to manage toothfish populations, as well as fish, seabirds and marine mammals that interact with fishing activity.
The shallow banks of the plateau support a spectacular diversity of long-lived sponges, brittle stars, anemones, soft and hard corals and crustaceans. These fragile and slow-growing communities are vulnerable to disturbance. Fishing gear fitted with automated video cameras helps locate and protect sensitive areas, and Australia and France have established marine reserves and managed areas across the plateau.
A unique underwater oasis
The plateau’s islands are incredibly isolated and provide the only breeding and land-based refuge for birds and seals in this part of the Southern Ocean.
Submarine volcanoes, some of them active, surround the islands and are particularly abundant around the younger McDonald Islands.
The plateau cuts across the strong current systems that sweep around the South Pole. This thrusts deep, cold water, enriched with volcanic minerals, to the surface then back to the seafloor. In turn, this powers a food chain stretching from small zooplankton to fish and predators such as Patagonian toothfish, penguins and albatross, and diving marine mammals such as elephant seals and sperm whales.
Carbon and nutrients returned to the seafloor support diverse communities of invertebrate and fish species that could not inhabit this location if not for the plateau.
The orientation and location of the Kerguelen Plateau make it a canary in the coalmine for understanding the southward shift in marine ecology due to climate change. As sea temperatures rise and ocean currents shift, plant and animal species will move south in search of cooler waters.
Recent modelling suggests those species most at risk from climate change in this region are those sedentary or slow-moving invertebrates, such as sea urchins.
Policy backed by science
Work continues to build comprehensive maps of the seafloor, deploy a network of ocean robots to collect physical and biological information, and use French and Australian fishing fleets for research.
The plateau’s waters are in the region overseen by the Commission for the Conservation of Antarctic Marine Living Resources, an international treaty body. French-Australian research is presented to the commission at meetings in Hobart each year to guide management decisions.
The cross-country partnership is a model for international scientific cooperation and fisheries management. In the context of a changing climate, these efforts will provide insight into future impacts on natural systems throughout the Southern Ocean.
Predicting when a volcano will next blow is tricky business, but lessons we learned from one of Hawaii’s recent eruptions may help.
Kīlauea, on the Big Island of Hawai’i, is probably the best understood volcano on Earth. That’s thanks to monitoring and gathered information that extends back to the formation of the Hawaiian Volcano Observatory in 1912.
The volcano is also subject to the world’s most technologically advanced geophysical monitoring network.
From the skies, satellites collect data that show the changing topography of the volcano as magma moves throughout the internal magma plumbing system. Satellites also look at the composition of volcanic gases.
From the ground, volcanologists use a number of highly sensitive chemical and physical tools to further understand the structure of that magma plumbing system. This helps to study the movement of magma within the volcano.
Earthquakes and vibrations
A lynch pin of volcano monitoring is seismicity – how often, where and when earthquakes occur. Magma movement within the volcano triggers earthquakes, and putting together the data on their location (a technique known as triangulation) tracks the path of magma underground.
A newer technique, seismic interferometry, uses vibrations of energy from ocean waves hitting the distant shorelines that then travel through the volcano.
Changes in the speed of these vibrations help us map the 3D footprint of the volcano’s magma plumbing system. We can then detect when, and in some cases how, the magma plumbing system is changing.
This monitoring provides the “pulse” of the volcano during times of inactivity – a baseline from which to detect change during volcanic unrest. This proved invaluable for early warning, and the prediction of where and when, of the eruption of Kīlauea on May 3, 2018.
The “pulse” of Kīlauea includes cycles of volcano inflation (bulging) and deflation (contraction) as magma moves into and out of the storage region at the summit of the volcano.
The speeds of vibrations travelling through the volcano are predictable during observations of inflation/deflation cycles. When the volcano bulges, the vibrations travel faster through the volcano as rock and magma is compressed. When the volcano contracts these speeds decrease.
We describe this relationship between the two sets of data – the bulging/contraction and the faster/slower speed of vibrations – as coupled.
Compared to our baseline, we saw the coupled data shift 10 days before the Kīlauea eruption on May 3. That told scientists the magma plumbing system had changed in a significant way.
The volcano was bulging due to the buildup of pressure inside the magma chamber, but the seismic waves were slowing down quite dramatically, instead of speeding up.
Our interpretation of this data was that the summit magma chamber was not able to sustain the pressure from an increasing magma supply – the bulge was too big. Rock material started to break around the summit magma chamber.
Breakage of the rocks perhaps then led to changes of the summit magmatic system so that more magma could more easily arrive at the eruption site about 40km away.
As well as Kīlauea, such coupled data sets are regularly collected, investigated and interpreted in terms of magma transport at other volcanoes globally. Sites include Piton de la Fournaise on Reunion Island, and Etna volcano, Italy.
But our modelling was the first to demonstrate these changes in the coupled data relationship could occur due to weakening of the material inside the volcano before an eruption.
The damage model that we applied can now be used for other volcanoes in a state of unrest. This adds to the toolbox volcanologists need to predict the when and where of an impending eruption.
So much data, we need help
When volcanoes are in a heightened state of unrest, the volume of information available from digital data and ground observations is extreme. Scientists tend to rely on observational monitoring first, and other data when time and extra people are available.
But the total amount of incoming data (such as from satellites) is overwhelming, and scientists simply can’t keep up. Machine learning might be able to help us here.
Artificial intelligence is the new kid on the block for eruption prediction. Neural networks and other algorithms can use high volumes of complex data and “learn” to distinguish between different signals.
Automated early alert systems of an impending eruption using sensor arrays exist for some volcanoes today, for example at Etna volcano, Italy. It’s likely that artificial intelligence will make these systems more sophisticated in the future.
Early detection sounds wonderful for authorities charged with public safety, but many volcanologists are wary.
If they lead to multiple false alarms then that could slash trust in scientists for both managers of volcanic crises and the public alike.
Just like a teenager wanting to be older, volcanoes can lie about their age, or at least about their activities. For kids, it might be little white lies, but volcanoes can tell big lies with big consequences.
Our research, published today in Nature Communications, uncovers one such volcanic lie.
Accurate dating of prehistoric eruptions is important as it allows scientists to correlate them with other records, such as large earthquakes, Antarctic ice cores, historical events like Mediterranean civilisation milestones, and climatic events like the Little Ice Age. This gives us a better understanding of the links between volcanism and the natural and cultural environment.
Taupo’s last violent eruption
Lake Taupo, in the North Island of New Zealand, is a globally significant caldera supervolcano. The caldera formed after the collapse of a magma chamber roof following a massive eruption more than 20,000 years ago.
Now it seems that the Taupo eruption that occurred in the early part of the first millennium has been lying about its age. But like many lies, it was eventually found out, and it reveals exciting processes we hadn’t understood before.
The eruption of Taupo in the first millennium has been dated many times with radiocarbon, yielding a surprisingly large spread of ages between 36CE and 538CE.
Curious Kids: Why do volcanoes erupt?
Radiocarbon dating of eruptions
Radiocarbon dating of organic material is based on the concentrations of radioactive carbon-14 in a sample remaining after the organisms’ death. Over the past two decades, the method has been refined greatly by combining it with dendrochronology, the study of the environmental effects on the width of tree rings through time.
Radiocarbon dating of tree ring records has allowed scientists to construct a reliable record of the concentration of carbon-14 in the atmosphere through time.
In principle, this composite record allows eruptions to be dated by matching the wiggly trace of carbon-14 in a tree killed by an eruption to the wiggly trace of atmospheric carbon-14 from the reference curve (“wiggle-match” dating).
Scientists presently use wiggle-match dating as the method of choice for eruption dating, but the technique is not valid if carbon dioxide gas from the volcano is affecting a tree’s version of the wiggle.
The effect of volcanic carbon on eruption ages
Our study re-analysed the large series of radiocarbon dates for the Taupo eruption and found that the oldest dates were closest to the volcano vent. The dates were progressively younger the farther away they were.
This unusual geographic pattern has been documented very close (i.e. less than a kilometre) to volcanic vents before, but never on the scale of tens of kilometres. Two wiggle match ages, taken from the same forest, located about 30km from the caldera lake, were among the oldest dates from the series of dates.
This enlarged influence of the volcano can be explained by the influence of groundwater beneath the lake and its surroundings. The Taupo wiggle-match tree grew in a dense forest in a swampy valley where volcanic carbon dioxide was seeping out of the ground and was incorporated in the trees.
The ratio of carbon-13 to carbon-12 (the two stable isotopes of carbon) in the modern water of Lake Taupo and the Waikato River tells us that volcanic carbon dioxide is getting into the groundwater from an underlying magma body.
Can large eruptions be forecast over decades?
Our study shows that a large and increasing volume of carbon dioxide gas containing these stable isotopes was emitted from deep below the prehistoric Taupo volcano. It was then redistributed by the region’s huge groundwater system, ultimately becoming incorporated into the wood of the dated trees.
The increase was sufficiently large over several decades to dramatically alter the ratios of different carbon isotopes in the tree wood. The forest was subsequently killed by the last part of the Taupo eruption series. But the dilution of atmospheric carbon-14 by volcanic carbon made the radiocarbon dates for tree material from the Taupo eruption appear somewhere between 40 and 300 years too old.
The precursory change in carbon ratios gives us a way to gain insight into the forecasting of future eruptions, a central goal in volcanology. We found that the radiocarbon dates and isotope data that underpin the presently accepted “wiggle match” age reached a plateau (that is, stopped evolving normally). This meant that for several decades before the eruption, the outer growth rings of trees had ‘weird’ carbon ratios, forecasting the impending eruption.
We re-analysed data from other major eruptions, including at Rabaul in Papua New Guinea and Baitoushan on the North Korean border with China and found similar patterns. The anomalous chemistry mimics but exceeds the Suess effect, which reversed the carbon isotopic evolution of post-industrial wood. This implies that measurements of carbon isotopes in 200-300 annual rings can track changes in the carbon source used by trees growing near a volcano, providing a potential method of forecasting future large eruptions.
We anticipate that this will provide a significant focus for future research at supervolcanoes around the globe.
Spectacular images of recent volcanic eruptions in Hawaii are a little disheartening – especially given news reports suggesting there is a sleeping volcano under Melbourne that could awaken and erupt at any moment.
Understanding the geological differences between Melbourne and Hawaii is really helpful in working out how we can keep an eye on future risks in Australia.
The Newer Volcanics Province
Victoria and South Australia do host an active volcanic field, called the Newer Volcanics Province (NVP). This is not a single volcano with a large single chamber of molten rock (magma) — the common image of a volcano — but a widespread field of multiple small volcanoes, each with a small volume of magma.
Melbourne lies at the eastern end of the NVP, and the most recent eruptions in this area occurred over a million years ago.
Mt Gambier in southeastern South Australia represents the western margin of the volcanic field and the most recent eruption — only 5,000 years ago.
Between Melbourne and Mt Gambier there are more than 400 small volcanoes that erupted over a period of 6 million years.
The NVP was most active between 4.5 million to 5,000 years ago and volcanologists consider the field to still be “active” with the potential for future eruptions.
We do not know when the next eruption will take place.
The NVP is located within a tectonic plate – and not along a plate edge like the Ring of Fire volcanoes (for example, Mt Agung on Bali).
Tectonic plates are large slabs of rock made up of the Earth’s crust and uppermost part of the mantle (the lithosphere) which form the outer shell of the Earth, and move around slowly relative to each other.
Curious Kids: Why do volcanoes erupt?
Volcanoes act in different ways
While Kilauea volcano in Hawaii is also located within a tectonic plate, it has several key differences with the NVP in Southeastern Australia.
Magma source and volume
While Hawaii sources large volumes of magma from deep within the Earth, the NVP only receives small amounts of magma from just below the Earth’s crust.
It’s worth noting here that the makeup of the magma is similar in both locations, with both erupting runny basalt – a type of rock low in silica, and high in iron and magnesium.
We suspect that in Australia’s NVP, magma can move very fast from its source to the surface (on a time scale of days). This can bring rock fragments of the mantle (xenoliths) to the surface as the magma moves too fast for them to melt.
Hawaiian volcanoes can erupt numerous times, but NVP volcanoes are largely monogenetic — that is, each only erupt once or over a restricted period of time.
Hawaii is located on the oceanic crust of the Pacific Tectonic Plate, which is a thin (around 7 km) layer of material that is dense and rich in iron. The magma can rise through this crust quite easily.
In contrast, the NVP is located on continental crust which is much thicker (about 30km), richer in silica and much less dense. Magma finds it much harder to travel through this kind of material.
Is there a new volcano on Hawaii?
Water adds danger
The explosivity of a volcanic eruption can depend on availability of water.
“Dry” eruptions – where magma has little-to-no interaction with ground water or water on the Earth’s surface – typically produces mildly explosive eruptions such as lava fire fountains, showers of lava fragments and lava flows.
The most explosive, hazardous eruptions form where rising magma interacts with ground water, surface water or sea water. These “wet”, (phreatomagmatic) eruptions can produce deadly, fast moving, ground-hugging currents of gas and volcanic material – called pyroclastic surges, and send abundant fine volcanic ash into the atmosphere.
The Australian Mt Gambier eruption 5,000 years ago was a “wet” eruption, and had a volcanic explosivity index of 4 on a scale of 0-8 (where 0 represents a lava eruption, 1 a spectacular lava “fire” fountain as recently witnessed in Hawaii, and 8 represents a catastrophic explosive super-eruption).
The accompanying ash column is estimated to have reached 5km to 10km into the atmosphere.
On Hawaii explosive eruptions are rarer because the magma has a low gas content and groundwater aquifers are not as large as in the NVP. However, when lava flows into the sea there are often phreatic or steam explosions which can be hazardous to nearby spectators.
There’s a lot we don’t know
Another important factor relates to how we keep an eye on volcano risk at the two sites. Kilauea on Hawaii is extremely well monitored, and tracking magma moving underground has helped predict eruptions.
In contrast, the NVP is less well monitored, likely because there is no present volcanic activity, and it’s a huge region.
However, warning signs of an eruption are likely to be similar in the NVP to those on Hawaii – small earthquakes, minor uplift and/or subsidence of the ground, changes in ground temperature and gas or steam rising out of the ground.
Also, based on present knowledge of the NVP, there is no clear eruption pattern we can use to try to predict when or where the next eruption will be.
If the NVP were to erupt, significant impacts on our lives would likely occur. These may include:
- the closure of surrounding roads by lava flows and ash fallout
- volcanic ash and rocks loading roofs of local buildings
- contamination of water reservoirs by ash
- damage to machinery and electricity infrastructure by infiltrating ash
- respiratory problems for people prone to asthma, and
- disruption to air traffic across southeastern Australia due to drifting ash clouds driven by prevailing south-westerly winds.
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Further scientific research is required on active volcanic fields such as the NVP to know how fast magma travels from its source to the surface, how much warning we might have before an eruption, and how long an eruption and its impacts might last.
Heather Handley, Associate Professor in Volcanology and Geochemistry, Macquarie University; Jozua van Otterloo, Assistant Lecturer in Volcanology, Monash University, and Ray Cas, Professor emeritus, Monash University
This is an article from Curious Kids, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky! You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.
Why do volcanoes erupt? – Nicholas, age 3 years and 11 months, Northmead, NSW.
The rock inside the planet we live on can melt to form molten rock called magma. This magma is lighter than the rocks around it and so it rises upwards. Where the magma eventually reaches the surface we get an eruption and volcanoes form.
The top part of the Earth is made up of a number of hard pieces called tectonic plates. Magma and volcanoes often form where the plates are pulled apart or pushed together but we also find some volcanoes in the middle of tectonic plates.
Volcanoes have many different shapes and sizes, some look like steep mountains (stratovolcanoes), others look like bumps (shield volcanoes) and some are flat with a hole (a crater or caldera) in the centre that is often filled with water.
The shape of the volcano and how explosively it erupts depend largely on how “sticky” and how “fizzy” (how much gas) the magma is that is erupted.
For example, if you try to blow bubbles in cooking oil though a straw, the bubbles can escape quite easily because the cooking oil is runny.
If you try to blow bubbles in jam or peanut butter you would find it very difficult because the jam and peanut butter are very sticky, they wouldn’t move much at all if you tried to pour them out of the jar.
It is the same with volcanoes. When magma rises towards the surface gas bubbles start to form. Whether or not they can escape as the magma is rising affects how explosive the eruption will be.
Where the magma is runny like cooking oil and doesn’t have much bubbly gas mixed in it, such as places like Hawaii, then we see lots of slow-moving lava flows and shield volcanoes. Lava is what we call magma when it reaches the surface.
Here are some pictures of a recent Hawaiian eruption:
However, where the magma is very sticky, like jam or peanut butter, and if it contains a lot of bubbly gas then the gas can get stuck and eruptions can be very powerful and explosive, like the recent eruptions at Fuego volcano in Guatemala.
Damage caused by eruptions
In explosive eruptions the frothy, bubbly magma can be ripped apart into tiny bits called volcanic ash. This is not ash like you get after a barbecue or fire, it does not crumble away in your fingers. It is very sharp and is dangerous to breathe in.
Some explosive volcanoes can send ash high up into the sky and it can travel around the world over different countries. If aeroplanes travel through an ash cloud from a volcano it can cause a lot of damage to the engine.
Other explosive eruptions create fast-moving, hot clouds of volcanic ash, gas and rocks that travel down the sides of the volcanoes and destroy pretty much everything in their path.
The benefits of volcanoes
Despite the great damage they can cause, volcanoes also help us to live. Volcanic ash provides food for the soil around volcanoes which helps us grow plants to eat. The heat from some volcanoes is used to make energy to power lights, fridges, televisions and computers in people’s houses.
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Recent photographs and video from the devastating eruption of Fuego volcano in Guatemala show people stood watching and filming hot, cloud-like flows of gas, ash and volcanic material (known as pyroclastic flows) travelling towards them down the slopes of the volcano.
From this it is clear that some people do not fully understand the risks of the volcanoes they live near.
Although each volcano is different, and each presents different risks to the people near to them, there are some generalisations that help us understand what these risks are likely to be.
Three points are clear: location matters, explosiveness can be predicted to an extent, and fast-moving pyroclastic flows of volcanic material are deadly.
1. Location matters
The outer layer of the Earth, called the lithosphere (crust and upper mantle), is broken up into a number of rigid tectonic plates. Volcanoes typically occur where the plates move apart from one another, for example at underwater mid-ocean ridges, or collide together at subduction zones.
We also find volcanoes in the middle of tectonic plates – these are called “intraplate” volcanoes, such as the Hawaiian and Galápagos oceanic islands.
The magma (molten rock) that feeds volcanoes is generated in different ways in these settings, and different volcanic landforms result.
Hawaii is in the middle of a tectonic plate and volcanic activity there forms relatively low-profile, shield volcanoes. Typically, these volcanoes are built up by many fluid lava flows into broad, gently sloping domes, which resemble a warrior’s shield.
In contrast, Fuego is situated in a subduction zone environment (one plate going under another) where steep-sided, stratovolcanoes, or composite volcanoes are most common. These often symmetrical, conical volcanoes form from the build up of layers of lava and pyroclastic (fragmented volcanic) rocks.
2. Magma and gas affect explosiveness
The volcanic landforms and eruptive styles we see in different settings are largely a result of the differences in the composition of the magma (molten rock) erupted, its temperature and its gas content in these contrasting tectonic settings.
Large shield volcanoes in the middle of tectonic plates, such as Kilauea volcano in Hawaii, erupts high temperature, low silica lava. This is runnier (less viscous) than magma typically erupted at subduction zone volcanoes (like Fuego).
This means that any volatiles (dissolved gases such as water, carbon dioxide and sulphur dioxide) in the Kilauea magma are able to escape more easily compared to in a stickier, higher silica, magma that characterises subduction zone volcanoes.
And so “Hawaiian-style” eruptions are characterised by lava fountaining and flows of hot fluid lava that normally travel slow enough for people to walk away from and evacuate. This is exactly what we have been seeing over the last month in Kilauea’s East Rift Zone.
In contrast, at subduction zone volcanoes – such as Fuego – the higher water content of the magma and the typically more silica-rich, sticky magmas erupt more explosively. It is harder for gas bubbles formed to escape as magma rises to the surface, which then take up more space and over pressure the system.
Subduction zone volcanoes can produce high columns of gas and ash reaching tens of kilometres into the atmosphere, and scalding hot, fast-moving, cloud-like currents of gas, ash and volcanic material. These pyroclastic flows, or “pyroclastic density currents”, race down the volcano at speeds over 80 km/hr.
Some news reports of eruptions at Fuego have incorrectly termed these pyroclastic flows “rivers of lava”. They are very different to lava flows and much more hazardous.
Clear and accurate communication of volcanic eruptions is crucial if those near the volcano are to understand the real risks.
3. Pyroclastic flows are deadly
Pyroclastic flows are extremely hazardous and deadly. They were responsible for deaths in Pompeii and Herculaneum from the AD79 eruption of Vesuvius in Italy.
Even the famous volcanologists Katia and Maurice Kraft underestimated the reach of a pyroclastic flow during an eruption at Unzen volcano on June 3, 1991, which killed them along with many others.
Historic subduction zone volcanic eruptions producing devastating pyroclastic flows include:
- Vesuvius, Italy AD 79
- Tambora, Indonesia (1815)
- Krakatau (Krakatoa), Indonesia (1883)
- Mt Pelée, Caribbean (1902)
- Mt St Helens, USA (1980)
- Mt Pinatubo, Philippines (1991)
- Unzen, Japan (1991).
At Fuego, the loose, fragmented volcanic material (known as tephra) lying on the slopes after eruptions may be remobilised by rain to form volcanic mudflows known as lahars. These pose a significant current and future risk for the people surrounding Fuego compared to those living in Hawaii.
Pyroclastic density currents were the main cause of death from volcanic activity in the 20th Century, killing around 45,000 people, almost 50% of all volcanic deaths in that time period (total deaths from volcanic activity is estimated to be 91,724).
While eyes are diverted toward eruptions in Central America and the Pacific Ocean, Indonesia has raised the alert level on some of its volcanoes this week. It now has 21 volcanoes on alert levels 2-4 (yellow, orange and red) on a scale of 1-4.
Local authorities will be vital in managing and communicating the risks of these volcanoes, as well as around Fuego and Kilauea.
Over the past few weeks we’ve seen increasingly spectacular images reported in the news of the ongoing eruption at Kilauea volcano, on the Pacific island of Hawai’i.
These have been tempered by reports of growing destruction, with houses and infrastructure bulldozed, buried or burned by lava flows.
Yet Kilauea is one of the world’s most active volcanoes, and has been erupting continually since 1983. So what has triggered this sudden change in activity, threatening homes and livelihoods? The answer relates to what is happening beneath the volcano.
Activity at Kilauea is driven by the buoyant upwelling of a plume of hot mantle, which provides the heat to generate magma beneath the volcano. This magma has the potential to erupt from several different locations, or vents, on the volcano.
Typically, the crater at the summit of the volcano is where eruptions are expected to occur, but the geology of Kilauea is complex and a rift on the eastern side of the volcano also allows magma to erupt from its flanks.
Over the past decade both the summit crater and a vent on the eastern rift, called Pu’u O’o, have been continually active. The summit crater has hosted a lava lake since March 2008.
Lava lakes are relatively rare features seen at only a handful of volcanoes around the world. The fact that they do not cool and solidify tells us that lava lakes are regularly replenished by fresh magma from below.
In contrast, Pu’u O’o, 18km east of the summit crater, has been pouring out lava flows since 1983. In the first 20 years of this eruption, 2.1km³ of lava flows were produced, equivalent in volume to 840,000 Olympic swimming pools. All of this tells us that Kilauea volcano regularly receives lots of magma to erupt.
Over the past three weeks activity at Pu’u O’o has stopped, while a series of fissures has opened roughly 20km further east in a subdivision known as Leilani Estates.
This area was previously affected by lava flows in 1955.
To date, 23 fissures have opened, starting off simply as cracks in the ground, with some developing into highly active vents from which significant lava flows are forming.
Meanwhile, at the summit of the volcano, the lava lake has drained from the crater, sparking fears of more explosive eruptions, as draining magma interacts with groundwater.
Satellite instruments and high-resolution GPS are being used to monitor changes in the shape of the volcano and have found that the summit region is deflating, while the lower east rift zone, where new fissures have opened in recent days, is inflating.
The magma reservoirs that feed eruptions on Kilauea can be imagined as balloons, which grow when they are filled and shrink when they are emptied. Deflation at the summit, combined with observations that the lava lake has drained (at a rate of up to 100m over two days!), suggest that the magma reservoir feeding the summit is emptying.
Where is the magma going? Observations of ground inflation around the newly opened fissures to the east indicate that the magma is being diverted down the east rift and accumulating and erupting there instead.
Exactly what has caused this rerouting of the magma is still not clear. A magnitude 6.9 earthquake occurred in the area on May 4 and this may have opened a new pathway for magma to erupt, influencing the geometry of the lower east rift zone.
Lessons for the future
By combining measurements from Kilauea of ground deformation, earthquake patterns and gas emissions during the current eruption, with observations of the lava that is erupted, volcanologists will be able to piece together a much clearer picture of what triggered this significant change in eruption over the past few weeks.
This knowledge will be crucial in planning for future eruptions, both at Kilauea and at other volcanoes.
Eruptions from the flanks of a volcano can pose a much more significant hazard for the local population than those from a volcano’s summit, as many more people live in the areas that are directly affected.
This has been amply displayed over the past few weeks on Kilauea by the fissures opening in people’s gardens and lava flows destroying homes and infrastructure.
But Kilauea is not the only volcano to have flank eruptions. For example, lava flows famously emerged from the lower slopes of Mt Etna in 1669, destroying villages and partially surrounding the regional centre of Catania, on the east coast of Sicily, Italy.
Lessons learned from the current eruption of Kilauea can equally be applied to other volcanoes, like Etna, where more densely populated surroundings mean that the hazards posed by such an eruption would be even greater.