There she blows: the internal ‘magma filter’ that prompts ocean island volcanoes to erupt

Laura Becerril, Author provided

Teresa Ubide, The University of QueenslandThe volcanoes we see on Earth’s surface are just the tip of the iceberg. Beneath the surface, they are fed by a complex network of conduits and reservoirs that bring molten rock, called magma, to the surface.

When the magma erupts, it can generate lava flows that cool down to become volcanic rocks. These rocks hold key clues about volcanoes’ inner workings, and what triggered them to erupt in the past. But decoding these clues is a puzzling task.

Our new research, published in the journal Geology, reveals previously hidden information in the chemistry of erupted lavas. Intriguingly, we discovered that many volcanoes have an internal “filter” that prompts them to erupt.

If we can detect magma at this crucial tipping point inside the volcano, it might even help us detect when an eruption is imminent.

Hotspot volcanoes

Most volcanoes, such as those in the Pacific Ring of Fire and the mid-Atlantic, are at the boundaries between tectonic plates. But some volcanoes, including the ones that created the Hawaiian islands, occur where hot plumes from deep inside Earth reach the surface. These are known as “hotspot” volcanoes.

Australia hosts the longest track of hotspot volcanoes in a continental setting. Over tens of millions of years, volcanoes such as The Glass House Mountains in Queensland, or Wollumbin (Mount Warning) in New South Wales, tracked the movement of the Australian continent over a stationary hotspot.

In the oceans, hotspots build chains of paradise islands such as Hawaii, the Galapagos or the Canary Islands. These ocean island volcanoes were previously thought to have been made of magma that welled up from tens of kilometres beneath the surface, deep in Earth’s mantle.

But our new research suggests ocean island volcanoes may erupt magma that has been filtered and modified at shallower depth.

Crystal-rich, not crystal clear

Volcanic lavas often contain crystals from inside the volcano, that were mixed in with the erupting magma. The crystals tell us a lot about the volcano’s insides, but they can also disguise the chemistry of the lava itself.

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Volcano crystals could make it easier to predict eruptions

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Think of it like rocky road chocolate. If we want to analyse the ingredients of the chocolate itself, we first need to disregard the marshmallows and nuts.

Microscopic image of crystals in magma.
Author provided

We can do this by analysing rocks made from crystal-free lavas. In our study, we compared crystal-free and crystal-rich magmas from El Hierro volcano in the Canary Islands, which last erupted in 2011.

It turns out that the crystal-free magma from these volcanoes is very similar across millions of years of volcanic activity, and across many ocean island volcanoes around the world, including the Canary Islands and Hawaii. This is how we realised the magma was not pristine and coming directly from great depth, but rather filtered at shallower depths.

And if the magma from hotspot island volcanoes is so similar, the chances are their eruptions are triggered by common mechanisms too.

The ‘secret volcano filter’

When crystals form inside the volcano, this “steals” chemical elements from the magma. In turn, this alters the composition of the leftover magma, almost as if it had been passed through a sieve.

This filtering process makes the magma less dense, and increases its gas content. This gas can then bubble up and propel the magma to the surface, just like the cork popping from a bottle of champagne.

In ocean island volcanoes, the magma can reach this “tipping point” at the base of the Earth’s crust, just a few kilometres beneath the surface, rather than at depth.
This means that if we detect magma at this depth with the help of earthquake monitoring equipment, an eruption might follow. This is exactly what happened when El Hierro erupted in 2011.

Does this make it easier to forecast eruptions?

If we could open a volcano like a doll’s house, we would be able to track the movement of magma towards the surface. It’s a pity we can’t, although we can try to “see” this journey indirectly, by monitoring earthquakes, deformation and gas emissions, all of which can indicate magma rising inside a volcano.

But to assess whether a volcano is likely to erupt, or whether a dormant volcano is reawakening, we also need to compare current observations with information about what triggered eruptions in the past.

This is where our new discovery could prove especially useful. If the eruption triggers happen at similar depths in ocean island volcanoes globally, warning signs from such depths may be particularly important to monitor and consider as the precursory signs of eruption.

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Read more:
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Teresa Ubide, Senior Lecturer in Igneous Petrology/Volcanology, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Krakatoa is still active, and we are not ready for the tsunamis another eruption would generate

Deni_Sugandi / shutterstock

Ravindra Jayaratne, University of East London

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.

Krakatoa is in the middle of a narrow strait between Java and Sumatra. Indonesia’s capital Jakarta is about 100 miles to the east.
ChrisO wiki / CIA World Factbook / Demis

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.

The tsunami badly damaged buildings on Legundi island, 20 miles from Krakatoa.
Ravindra Jayaratne, Author provided

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.

Head to the hills.
Ravindra Jayaratne, Author provided

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.

Ravindra Jayaratne, Reader in Coastal Engineering, University of East London

This article is republished from The Conversation under a Creative Commons license. Read the original article.

New Zealand’s White Island is likely to erupt violently again, but a new alert system could give hours of warning and save lives

Jorge Silva/Reuters

David Dempsey and Shane Cronin

Tourists visiting Whakaari/White Island on December 9 last year had no warning of its imminent violent eruption. The explosion of acidic steam and gases killed 21 people, and most survivors suffered critical injuries and severe burns.

The tragedy prompted us to develop an early alert system. Our research shows patterns of seismic activity before an eruption that make advance warning possible. Had our system been in place, it would have raised the alert 16 hours before the volcano’s deadly eruption.

Ash covers the ground after Mt Tongariro erupted overnight on August 7 2012.
NZ Police

We were also motivated by the fact that several other New Zealand volcanoes pose similar threats. Explosions and surges at the popular visitor destination Waimangu geothermal area killed three people in 1903, an eruption at Raoul Island in 2006 killed one person, ballistics at Mt Ruapehu in 2007 caused serious injuries and tourists narrowly escaped two eruptions on a popular day walk in the Tongariro national park in 2012.

Our automated warning system provides real-time hazard information and a much greater level of safety to protect tourists and help operators determine when it is safe to visit volcanoes.

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Read more:
Why White Island erupted and why there was no warning

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This image of the 2019 eruption of Whakaari White Island eruption was taken by a visitor.
Michael Schade/AAP

A history of eruptions

New Zealand has a network of monitoring instruments that measure even the smallest earth movements continuously. This GeoNet network delivers high-rate data from volcanoes, including Whakaari, but it is not currently used as a real-time warning system for volcanic eruptions.

Although aligned with international best practice, GeoNet’s current Volcano Alert Level (VAL) system is updated too slowly, because it relies mainly on expert judgement and consensus. Nor does it estimate the probability of a future eruption — instead, it gives a backward view of the state of the volcano. All past eruptions at Whakaari occurred at alert levels 1 or 2 (unrest), and the level was then raised only after the event.

Our study uses machine learning algorithms and the past decade of continuous monitoring data. During this time there were five recorded eruptions at Whakaari, many similar to the 2019 event. Since 1826, there have been more than 30 eruptions at Whakaari. Not all were as violent as 2019, but because there is hot water and steam trapped in a hydrothermal area above a shallow layer of magma, we can expect destructive explosions every one to three years.

A memorial in Whakatane, following the White Island eruption in 2019.
Jorge Silva/Reuters

Last year’s eruption was preceded by 17 hours of seismic warning. This began with a strong four-hour burst of seismic activity, which we think was fresh magmatic fluid rising up to add pressure to the gas and water trapped in the rock above.

This led to its eventual bursting, like a pressure cooker lid being blasted off. A similar signal was recorded 30 hours before an eruption in August 2013, and it was present (although less obvious) in two other eruptions in 2012.

Building an early warning system

We used sophisticated machine-learning algorithms to analyse the seismic data for undiscovered patterns in the lead-up to eruptions. The four-hour energy burst proved a signal that often heralded an imminent eruption.

We then used these pre-eruption patterns to teach a computer model to raise an alert and tested whether it could anticipate other eruptions it had not learned from. This model will continue to “learn by experience”. Each successive event we use to teach it improves its ability to forecast the future.

We have also studied how best to optimise when alerts are issued to make the most effective warning system. The main trade-off is between a system that is highly sensitive and raises lots of alerts versus one that sets the bar quite high, but also misses some eruptions.

We settled on a threshold that generates an alert each time the likelihood of an eruption exceeds 8.5%. This means that when an alert is raised – each lasting about five days – there is about a 1-in-12 chance an eruption will happen.

This system would have raised an alert for four of the last five major eruptions at Whakaari. It would have provided a 16-hour warning for the 2019 eruption. But these evaluations have been made with the benefit of hindsight: forecasting systems can only prove their worth on future data.

We think there is a good chance eruptions like the 2019 event or larger will be detected. The trade-off is that the alerts, if acted upon, would keep the island off-limits to visitors for about one month each year.

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Read more:
Call for clearer risk information for tourists following Whakaari/White Island tragedy

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Where to from here

We have been operating the system for five months now, on a 24/7 basis, and are working with GNS Science on how best to integrate this to strengthen their existing protocols and provide more timely warnings at New Zealand volcanoes.

The Tongariro crossing is one of New Zealand’s most popular day walks and receives thousands of visitors each year.
EPA

We plan to develop the system for New Zealand’s other active volcanoes, including Mt Tongariro and Mt Ruapehu, which receive tens of thousands of visitors each year. Eventually, this could be valuable for other volcanoes around the world, such as Mt Ontake in Japan, where a 2014 eruption killed 63 people.

Because of the immense public value of these kinds of early warning systems, we have made all our data and software available open-source.

Although most eruptions at Whakaari appear to be predictable, there are likely to be future events that defy warning. In 2016 there was an eruption that had no obvious seismic precursor and this would not have been anticipated by our warning system.

Eruptions at other volcanoes may be predictable using similar methods if there is enough data to train models. In any case, human operators, whether assisted or not by early warning systems, will continue to play an important role in safeguarding those living near or visiting volcanoes.

David Dempsey, Senior Lecturer in Engineering Science and Shane Cronin, Professor of Earth Sciences

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Australia’s only active volcanoes and a very expensive fish: the secrets of the Kerguelen Plateau

Evening light on a Heard Island icescape. The island is part of the Kerguelen Plateau, which is being jointly studied by France and Australia.
Matt Curnock

James Dell, University of Tasmania

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.

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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.

Bird activity behind a research vessel near the Kerguelen Plateau.
Paul Tixier

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.

A location map of the Heard and Macquarie islands.
AAD

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.

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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.

Patagonian toothfish are prized in the restaurant industry for their rich flesh.

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.

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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.

King penguins at Corinthian Bay, Heard Island.
Matt Curnock

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.

James Dell, Post Doctoral Fellow, University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Climate explained: how volcanoes influence climate and how their emissions compare to what we produce

Rapid and voluminous volcanic eruptions around 252 million years ago can be linked with a mass extinction event.
from http://www.shutterstock.com, CC BY-ND

Michael Petterson, Auckland University of Technology

CC BY-ND

Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.

If you have a question you’d like an expert to answer, please send it to climate.change@stuff.co.nz

Everyone is going on about reducing our carbon footprint, zero emissions, planting sustainable crops for biodiesel etc. Is it true what the internet posts say that a volcano eruption for a few weeks will make all our efforts null and void?

The pretext to this question is understandable. The forces of nature are so powerful and operate at such a magnitude that human efforts to influence our planet may seem pointless.

If one volcanic eruption could alter our climate to such a degree that our world rapidly becomes an “icehouse” or a “hothouse”, then perhaps our efforts to mitigate anthropogenic climate change are a waste of time?

To answer this question we need to examine how our atmosphere formed and what geological evidence there is for volcanically induced climate change. We also need to look at recent data comparing volcanic and human greenhouse gas emissions.

There is evidence for catastrophic climate change from very large, protracted volcanic eruptions in the geological record. But in more recent times we have learned that volcanic emissions can lead to shorter-term cooling and longer-term warming. And the killer-punch evidence is that human-induced greenhouse gas emissions far exceed those of volcanic activity, particularly since 1950.

Forging Earth’s atmosphere

Let’s go back to first principles and look at where our atmosphere came from. Earth is 4.56 billion years old. The common consensus is that Earth’s atmosphere results from three main processes:

1. remnants of primordial solar nebula gases from the time of earliest planet formation

2. outgassing of the Earth’s interior from volcanic and related events

3. the production of oxygen from photosynthesis.

There have also been contributions over time from comets and asteroid collisions. Of these processes, internal planetary degassing is the most important atmosphere-generating process, particularly during the first of four aeons of Earth’s history, the hot Hadean.

Volcanic eruptions have contributed to this process ever since and provided the bulk of our atmosphere and, therefore, the climate within our atmosphere.

Next is the question of volcanic eruptions and their influence on climate. Earth’s climate has changed over geological time. There have been periods of an ice-free “hothouse Earth”. Some argue that sea levels were 200 to 400 metres higher than today and a significant proportion of Earth’s continents were submerged beneath sea level.

At other times, during a “snowball Earth”, our planet was covered in ice even at the equator.

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Climate explained: why we won’t be heading into an ice age any time soon

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What contribution have volcanic eruptions made to this variation in climate? As an example of a major influence, some scientists link mass extinctions to major volcanic eruption events.

The most famous such association is that of the eruption of volcanoes that produced the Siberian Traps. This is a large region of thick volcanic rock sequences, some 2.5 to 4 million square kilometres, in an area in Russia’s eastern provinces. Rapid and voluminous volcanic eruptions around 252 million years ago released sufficient quantities of sulphate aerosols and carbon dioxide to trigger short-duration volcanic winters, and long-duration climate warming, over a period of 10s of thousands of years.

The Siberian Trap eruptions were a causal factor in Earth’s largest mass extinction event (at the end of the Permian period), when 96% of Earth’s marine species and 70% of terrestrial life ceased to exist.

Natural climate change over past 100 million years

Geological evidence indicates that natural processes can indeed radically change Earth’s climate. Most recently (in geological terms), over the past 100 million years ocean bottom waters have cooled, sea levels fallen and ice has advanced. Within this period there have also been spells of a hotter Earth, most likely caused by (natural) rapid releases in greenhouse gases.

Homo sapiens has evolved during the past few million years largely during an ice age when up to two-kilometre-thick ice sheets covered large areas of the northern continents and sea levels were over 100 metres lower than today. This period ended 10,000 years ago when our modern interglacial warmer period began.

Astronomical cycles that lead to climate variations are well understood – for example, the Milankovitch cycles, which explain variations in Earth’s orbit around the sun, and the periodic nodding/swaying of our Earth’s axis. All of the geological and tectonic causes for this general longer-term Earth cooling are less well understood. Hypotheses include contributions from volcanoes and processes linked to the rise of the Himalayas and Tibet (from 55 million years ago).

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Specific volcanic eruptions and climate impacts

Researchers have studied specific volcanic eruptions and climate change. Mount Pinatubo (Philippines) produced one of the larger eruptions of recent times in 1991, releasing 20 million tonnes of sulphur dioxide and ash particles into the stratosphere.

These larger eruptions reduce solar radiation reaching the Earth’s surface, lower temperatures in the lower troposphere, and change atmospheric circulation patterns. In the case of Pinatubo, global tropospheric temperatures fell by up to 4°C, but northern hemisphere winters warmed.

Volcanoes erupt a mix of gases, including greenhouse gases, aerosols and gases that can react with other atmospheric constituents. Atmospheric reactions with volcanic gases can rapidly produce substances such as sulphuric acid (and related sulphates) that act as aerosols, cooling the atmosphere.

Longer-term additions of carbon dioxide have warming impacts. Larger-scale volcanic eruptions, whose ash clouds reach stratospheric levels, have the biggest climatic impacts: the larger and more prolonged the eruption period, the larger the impacts.

These types of eruptions are thought to have been a partial cause for the Little Ice Age period, a global cooling event of about 0.5°C that lasted from the 15th to the late 19th century. Super volcanoes such as Yellowstone (USA), Toba (Indonesia) and Taupo (New Zealand) can, theoretically, produce very large-volume eruptions that have significant climate impacts, but there is uncertainty over how long these eruptions influence climate.

Perhaps the strongest evidence for answering whether our (human) emissions or volcanoes have a stronger influence on climate lies in the scale of greenhouse gas production. Since 2015, global anthropogenic carbon dioxide emissions have been around 35 to 37 billion tonnes per year. Annual volcanic CO₂ emissions are around 200 million tonnes.

In 2018, anthropogenic CO₂ emissions were 185 times higher than volcanic emissions. This is an astounding statistic and one of the factors persuading some geologists and natural scientists to propose a new geological epoch called the Anthropocene in recognition that humans are exceeding the impacts of many natural global processes, particularly since the 1950s.

There is evidence that volcanoes have strongly influenced climate on geological time scales, but, since 1950 in particular, it is Homo sapiens who has had by far the largest impact on climate. Let us not give up our CO₂ emission-reduction aspirations. Volcanoes may not save the day.

Michael Petterson, Professor of Geology, Auckland University of Technology

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The ‘pulse’ of a volcano can be used to help predict its next eruption

The 2018 eruption of Kilauea volcano was preceded by damage of the magma plumbing system at the summit.
Courtesy of Grace Tobin, 60 Minutes, Author provided

Rebecca Carey, University of Tasmania

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.

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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 schematic of the deep magma plumbind system of Kilauea volcano, Big Island, Hawaii. Magma is transported from deep within the Earth and arrives in a series of summit magma reservoirs.
USGS

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.

Something changed

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.

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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.

Rebecca Carey, Senior Lecturer in Earth Sciences, University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Explosive lies: how volcanoes can lie about their age, and what it means for us

Lake Taupo, in the North Island of New Zealand, is a globally significant caldera of a supervolcano that formed following a massive eruption more than 20,000 years ago.
from http://www.shutterstock.com, CC BY-ND

Richard N Holdaway; Ben Kennedy, and Brendan Duffy, University of Melbourne

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.

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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.

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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 graph shows all of the ages obtained for the Taupo first millenium eruption, sorted by age, plotted on a digital model of the North Island of New Zealand. Lake Taupo is the caldera from which the eruption occurred. The oldest ages for the eruption are clustered around Lake Taupo, and older ages are located further from the volcano. We interpret this pattern as being caused by contamination of red areas with volcanic carbon dioxide.
Provided by authors, CC BY-ND

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.

This conceptual image shows how gas from the triggering event, decades before the eruption, works its way into the groundwater system and is eventually incorporated in the wood of the trees that we date.
Provided by authors, CC BY-ND

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.

Richard N Holdaway, Adjunct Professor; Ben Kennedy, , and Brendan Duffy, Lecturer in Applied Geoscience, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.