In the Bay of Naples, Europe's most notorious
giant is showing signs of reawakening from its long slumber. Campi Flegrei, a name that aptly translates as
"burning fields", is a supervolcano. It consists of a vast and complex
network of underground chambers that formed hundreds of thousands of
years ago, stretching from the outskirts of Naples to underneath the
Mediterranean Sea. About half a million people live in Campi Flegrei's
seven-mile-long caldera, which was formed by vast eruptions 200,000,
39,000, 35,000 and 12,000 years ago.
The past 500 years have been fairly peaceful ones for Campi Flegrei.
There have been no eruptions at all since 1538, and that was a
comparatively small event that resulted in the formation of the "New
Mountain", Monte Nuovo. But recent events suggest that this period of
quiescence may be coming to an end. An acceleration of processes causing deformation
and heating within the caldera saw the Italian government raise the volcano's threat level
in December 2016. Fears are growing that magma deep inside Campi
Flegrei could be reaching the "critical degassing pressure", where a
sudden large-scale release of volcanic gases could abruptly inject heat
into surrounding hydrothermal fluids and rocks. When this happens on a
significant scale, it can cause catastrophic rock failure within the
volcano, triggering an eruption. In line with this, a study published in May 2017 found evidence that the supervolcano has been building towards an eruption for decades. But the difficult question is not if, but when, and just how big an event this would be.
The Bay of Naples was formed thanks to several enormous volcanic explosions. Credit: iStock.
"Campi Flegrei is in a critical state," says Antonio Costa
of the National Institute of Geophysics and Volcanology in Bologna, who
is part of a team monitoring the supervolcano. "In probabilistic terms,
we expect something called a 'violent Strombolian eruption'. This is
relatively small-scale to a supereruption. However, it's not easy to say
if there will definitely be an eruption in the coming years. Campi
Flegrei has not erupted during the timescale that it's been under
observation, so we don't know entirely what to expect." A violent Strombolian eruption would blast
molten rock and volcanic gases a few thousand feet into the atmosphere.
It would surely be a major event, potentially requiring the evacuation
of hundreds of thousands of people. But in the context of Campi
Flegrei's past, it would be minor. The volcano's most notorious supereruption was
the Campanian Ignimbrite eruption, which occurred some 39,000 years ago.
It punched an estimated 300 cubic kilometres of molten rock 70km up
into the stratosphere, along with an estimated 450,000 tons of sulphur
dioxide. The ash cloud was carried as far as central Russia, some
2,000km away. The eruption occurred at a time when much of
Europe was already going through a lengthy glacial period, and the
consequences are thought to have devastated much of the continent for
centuries. Entire swathes of land, including Italy, the
Mediterranean coast and the entirety of eastern Europe, were left
covered in up to 20cm of ash. This would have destroyed vegetation and
created a vast desert. Much of Russia was immersed in 5cm of ash, enough
to disrupt plant life for decades or more. "We know from chemical analysis that the ash
contained fluorine, which has a strong impact on vegetation, and it
would have produced a disease called fluorosis in animals," Costa says.
"This would have had a knock-on impact on humans." In addition, the huge quantity of sulphur
dioxide released would have created a volcanic winter. Sulphur dioxide
backscatters the Sun's radiation in the upper atmosphere, preventing it
from reaching the ground. The 1991 Mount Pinatubo eruption, one of the
biggest of the 20th Century, did exactly this, temporarily lowering the
global temperature by around 0.6C.
But the Campanian Ignimbrite eruption may have had a far greater
impact, with some scientists estimating that it decreased temperatures
in Europe by as much as 4C, drastically altering the climate for many years. The timing of this huge eruption is suspicious,
because many archaeologists believe that 39,000 years ago is roughly
when our cousins the Neanderthals died out in Europe.
It has long been speculated that the eruption triggered extreme
environmental conditions across Europe, contributing to the extinction
of the Neanderthals, at least in some regions. However, while the impact on the Neanderthals
was surely significant, many scientists now believe it is unlikely that
this single event was cataclysmic enough to wipe them out.
Archaeological evidence suggests that Neanderthals persisted in parts of
western Europe for some 10,000 years after the Campanian Ignimbrite
eruption. This may be because of the way the ash dispersed. "After the eruption, Neanderthal archaeological
sites are found only in France and Spain," Costa says. "This is probably
because these two areas were not affected by the eruption at all,
because the wind was blowing towards the east."
Much of eastern Europe was covered in a layer of ash from the eruptions. Credit: iStock.
There is even an argument that the eruption
could have benefited the Neanderthals, by delaying the arrival in Europe
of modern humans, who would have competed with them for resources. "To
reach western Europe, modern humans would have had to cross the Middle
East and the vast desert created by the eruption," says Costa. "It would
have taken many hundreds of years for this land mass to recover." For now, it is unclear how much damage Campi
Flegrei's last major eruption did. But it is far from the only
supervolcano on the planet. Earth's geological history is a catalogue of
apocalyptic-looking volcanic events. In south-west Colorado, there is a vast canyon
approximately 100km wide and one kilometre deep. It serves as the legacy
of one of the most explosive single events in the planet's history. La Garita Caldera was formed by an eruption nearly 28 million years ago, which expelled 5,000 cubic kilometres of molten rock. Fortunately for us, the tectonic plates in the
area have since rearranged themselves, so a repeat event is impossible.
But approximately 75,000 years ago in Indonesia, an eruption of similar
scale occurred, and the supervolcano responsible remains active. Situated in the midst of a mountain range in
northern Sumatra, the tranquillity and natural beauty of Lake Toba makes
it a popular tourist location. But this lake is actually an enormous
caldera, a footprint of the most extreme climatic event in human
history. "The Toba eruption was frankly as big as any in the past tens of millions of years," says Clive Oppenheimer
of the University of Cambridge, who studies some of Earth's biggest
volcanos. "It's a particularly prominent one, because it's within the
timeframe of modern humans, and the timing is quite critical, because it
occurs around the time that humans come out of Africa and spread across
Asia." But exactly what effect this had on the human race has been the subject of much controversy.
Eruptions like those at Campi Flegrei may have helped wipe out Neanderthals in Europe. Credit: iStock. In the 1990s, volcanologists discovered large ash deposits
from Toba in marine sediments scattered across the Indian Ocean. The
ash contained a chemical signature that could be traced back 75,000
years. Later studies found similar ash in the South China Sea, Arabian
Sea and even in Lake Malawi, some 7,000km away from Toba. The colossal scale of the eruption means that
volcanic gases from Toba are thought to have been ejected through both
hemispheres of the Earth's atmosphere, causing them to circulate all
around the world. But exactly which gases were emitted from Toba, and in
what quantities, is crucial to knowing its impact on the climate and
understanding what happened next. So far back in time, this is not
straightforward. "There's an ice core in Greenland where they
have a chemical record of how global temperatures went up and down over
the past 125,000 years," says archaeologist Sacha Jones
of the University of Cambridge, who has spent many years researching
Toba. "Distinct layers of ice are laid down each year, and people have
measured how much sulphate is in these layers. There is a large peak of
sulphate, which seems to correspond to the timeframe of Toba." If the Toba eruption did indeed send vast
quantities of sulphur dioxide around the world, scientists have
predicted it may have sparked a volcanic winter, which blackened the
skies and lasted several years. In line with this, geneticists studying
patterns in human mitochondrial DNA in the early 1990s, identified what appears to be a population bottleneck, which occurred somewhere between 50,000 and 100,000 years ago. Many were quick to make the link to Toba. But not everyone is so convinced. "Over the last 10 or so years, people have become more sceptical that Toba almost killed off Homo sapiens,"
Oppenheimer says. "Magmas can dissolve and hold things like carbon
dioxide and water and sulphur in different amounts, depending on the
volcano. And chemical analysis of ash from Toba has found that its magma
can't actually hold very much sulphur." There is also something suspicious in the
archaeological record. Indonesia, Malaysia and India are thought to have
been blanketed in at least 5cm of ash from Toba, which undoubtedly
affected vegetation and caused mass floods. Yet archaeological studies
of ash deposits appear to show that humans were remarkably resilient to
the environmental changes. "The main signs of human activity around this
time are stone tools of the Middle Palaeolithic period, such as points
and scrapers," says Jones, who has excavated sites
in the Jurreru Valley in Andhra Pradesh, India. "When we excavated
deposits above, through and below the Toba ash layer, we didn't really
see much change at all in these Stone Age technologies before and after
the eruption, which suggests that it didn't really cause any mass
extinction."
A supervolcano is likely to cause severe disruption to air travel. Credit: Getty Images.
The key factor may be that most of the ash from
Toba is believed to have fallen in the ocean, where it would have had
only minimal effects on land-dwelling species like humans. However,
Jones believes that the impact was still extremely severe for some
communities. “Toba was an incredibly large eruption, so it
would have devastated certain areas, particularly in the immediate
vicinity in Sumatra and elsewhere in Southeast Asia,” she says. “Yet in
areas like India, which is further afield but was still blanketed in
ash-fall, people were inhabiting a diverse range of habitats and
microclimates, in forests, desert fringes, plains and hill ranges. This
means that populations would have coped differently following Toba’s
aftermath, suffering in some areas more than others." But what of Toba's future? Geologists and
geophysicists who study the volcano remain concerned about its magma
chamber, which could be reawakened if the Sumatra fault line, which
bisects the island and runs through Mount Toba, became active. If it did, the only solution would be mass
evacuation. But we do not even know how much warning we would receive. Located underneath Yellowstone National Park in
the US, the Yellowstone supervolcano is one of the most actively
monitored places on the globe. A variety of instruments, including
seismometers to detect chains of earthquakes, GPS sensors to record how
the ground swells and shifts, and even satellite images to detect
pressure changes in the magma chamber, are all used to look for any
noticeable trends in behaviour. Yellowstone has had three supereruptions in the past 2.1 million years. The first remains one of the largest of all time, producing 2,500 times
the volume of ash as the 1980 Mount St Helens eruption. If Yellowstone
erupted again, some scientists think it would have more devastating
consequences than Toba, because the majority of the ash would fall on
land rather than in the sea. "The last eruption of Yellowstone would potentially have put ash across both American continents," says David Pyle
at the University of Oxford. "If you take a continental land mass and
you suddenly cover it with 10cm of volcanic ash, all the organic matter
and trees will lose their leaves and probably die. Animals will take in
chemicals which are toxic to them. The ground will suddenly be much
brighter than before, so a lot of the incoming solar radiation might
simply be reflected back into the atmosphere, resulting in a lengthy
drought." With water supplies clogged, electricity
transmission lines failing and a complete disruption in ground
transport, there would be an immediate crisis.
If Yellowstone's supervolcano exploded, it could devastate the West Coast of the US. Credit: iStock. "If Yellowstone, Campi Flegrei or Toba exploded,
there would be huge economic impact across the globe, because of the
way the world economy works now," Oppenheimer says. "We saw that after
the relatively small Icelandic eruption [Eyjafjallajökull] in 2010. It
affected supply chains for Volkswagen, because parts were coming from
Japan. Global aviation could be affected for decades. If a lot of
sulphur dioxide was released, this could precipitate monsoons and
climate shifts, which could affect global food security." This would all be very problematic, but
scientists are sceptical that a single explosive event like this could
actually wipe out humanity. Instead, volcanologists say that another type of
volcanic event may pose a much greater threat to our existence. Over the past 500 million years, all of the five largest mass extinctions in the fossil record have coincided with huge lava eruptions.
These eruptions did not happen as single events, but as continuous
outpourings going on for hundreds of thousands of years. They are known
as flood lavas, and are caused by rising plumes of hot material from
deep inside the Earth. The most violent flood lava eruptions are thought to be associated with continental drift.
Only 11 have taken place in the past 250 million years, each shaping
vast mountain ranges, plateaus or volcanic formations. One such flood
lava event took place 66 million years ago and created a huge expanse of
volcanic rock called the Deccan Traps, in west-central India. These
eruptions may have contributed to the mass extinction that took place at
this time, by releasing cocktails of gases that slowly acidified the
oceans and altered the climate. The trouble is, nobody knows when the next flood
lava event will occur. "We expect another flood lava event sometime in
the next 50 million years, but I don't think anyone's got any idea where
and when," Pyle says. Whether we are predicting the next supervolcano
eruption or the next flood lava event, the problem is the same. The
former has not been observed in recorded human history, while the last
major flood lava eruptions occurred 10 million years ago in southern
Canada, many millions of years before our species walked the planet. As
such, while the world's volcanic hotspots are supremely well-monitored,
we have no idea quite what to expect or how much warning we would
receive before an event of such scale. Our tiny snapshot of monitoring
time is dwarfed by volcanic cycles that can last millions of years. We have no real idea where we are on these
cycles. It is entirely possible that nothing will happen in our
lifetimes, or even in the next hundred thousand years. There is only one
certainty about these eruptions: they will, eventually, happen.
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