January 2013, Week 2


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Planetary Disasters: It Could Happen One Night

     Catastrophes from the past will strike again — we just do not know when.

Nicola Jones
January 8, 2013

One hundred thousand years ago, a massive chunk of the
Mauna Loa volcano cracked away from Hawaii and slid
into the sea, launching a wave that rose as high as the
Eiffel tower up the slopes of a nearby island. That
mega-tsunami was not an isolated incident: the past
40,000 years have seen at least ten gigantic landslides
of more than 100 cubic kilometres in the North Atlantic
ocean alone, each capable of producing waves tens to
hundreds of metres high. Another is bound to happen
sometime — although whether it will strike tomorrow or
10,000 years from now is anyone's guess.

This week, the World Economic Forum published its 2013
global risks report, which includes a section, produced
in collaboration with Nature, on X factors: low-
probability, high-impact risks resulting mainly from
human activity (see go.nature.com/outhzr). But the
natural world holds unpredictable threats as well. The
geologic record is peppered with evidence of rare,
monstrous disasters, ranging from asteroid impacts to
supervolcanoes to gamma-ray bursts. Nature looks into
some of the life-shattering events that Earth and the
broader Universe could throw our way.

Death by volcano

Earth is now in the middle of a flare-up of
supervolcanic activity[1]. Over the past 13.5 million
years, no fewer than 19 giant eruptions have each
spewed more than 1,000 cubic kilometres of rock —
enough to coat an entire continent in a few centimetres
of ash and push the planet into 'nuclear winter'. One
of the most recent such eruptions, of Toba in Indonesia
74,000 years ago, was such a catastrophic event that
some scientists have blamed it for starting the last
ice age and slashing the human population to about
10,000 people. One estimate1 suggests that there is a
1% chance of a super-eruption in the next 460–7,200

The four youngest, most active supervolcanic systems in
the world are Toba, Campi Flegrei in Italy, Yellowstone
in the northwestern United States and Taupo in New
Zealand. All four systems are being monitored for
groundswell and seismic swarms — clusters of small
earthquakes that can signal moving magma — and all
occasionally show these warning signs. But no one knows
whether the result of each flare-up will be a small
squirt of steam or — much more hazardous — a mega-
eruption of lava. “If something were brewing, we would
get warning hours, days and months ahead,” says Shan de
Silva, a volcanologist at Oregon State University in
Corvallis. “But how big it's going to be, we don't have
a handle on.”

To help answer these questions, scientists are now
drilling into the heart of one of the top contenders
for the next blow-up: the Campi Flegrei caldera, a
crater that is 13 kilometres wide and includes the city
of Naples. Since 1969, the ground at Campi Flegrei has
bulged upwards by as much as 3.5 metres, and
researchers are eager to find out whether the culprit
is underground steam or a pool of magma. Previous bouts
of volcanic activity in the caldera came after the
ground surface had swelled up by several metres or
more2, and researchers think that major activity could
occur within the next few decades or centuries. To
investigate the risk, scientists at Campi Flegrei plan
to drill more than 3 kilometres into the crater,
despite concerns from some researchers that the
drilling could trigger earthquakes or an explosion.

One goal is to look at the magma pool beneath the
crater: the shallower and more molten it is, the
greater the chances of a super-eruption. Characterizing
such pools through seismic studies is hard, and the
range of error is huge. “We really are groping in the
dark,” says de Silva. Scientists estimate that 10–30%
of the magma under Yellowstone, for example, is liquid
— shy of the 50% thought to be needed for super-
eruption. But pockets of molten magma in the chamber
could still cause eruptions several-fold larger than
the 1980 blast from Mount St Helens in Washington
state, warns Jacob Lowenstern, head of the Yellowstone
Volcano Observatory for the US Geological Survey in
Menlo Park, California.

The effort to drill into Campi Flegrei and measure
features such as temperature and rock permeability
should help researchers to interpret seismic-imaging
studies of magma pools, says Lowenstern. “If we want to
be able to successfully image Earth, we occasionally
need to make a few strategic incisions into the
patient,” he says. As for the dangers of drilling,
Lowenstern is convinced that the project will have
minimal impact. “It's like a pinprick on an elephant,”
he says. The Campi Flegrei team finished an initial
500-metre test well in December 2012 without incident.
And seismologists safely drilled a hole of similar size
into the Long Valley caldera in California — a
supervolcano site that erupted 760,000 years ago and
holds the same killer potential as Yellowstone.

Until more is learned about these systems, societies
must accept that the threat of a super-eruption is
real, yet remote. Lowenstern says that although the
chances of one happening this year are tiny, “it is
theoretically possible”.

Death by fungus

Although viruses and bacteria grab more attention,
fungi are the planet's biggest killers. Of all the
pathogens being tracked, fungi have caused more than
70% of the recorded global and regional extinctions3,
and now threaten amphibians, bats and bees. The Irish
potato famine in the 1840s showed just how devastating
such pathogens can be. Phytophthora infestans (an
organism similar to, and often grouped with, fungi)
wiped out as much as three-quarters of the potato crop
in Ireland and led to the death of one million people.

Potato blight is still a threat: 13_A2, a highly
aggressive strain of P. infestans, is now rampant in
Europe and North Africa. Across the globe, Phytophthora
causes some US$6.7 billion in annual damages, according
to a 2009 estimate4. Sarah Gurr, a plant pathologist at
the University of Oxford, UK, estimates that the worst
theoretical potato infestation would deprive 1.3
billion people of food each year. Other major staple
crops face similar threats, such as rice blast
(Magnaporthe oryzae), corn smut (Ustilago maydis), soya
bean rust (Phakopsora pachyrhizi) and wheat stem rust
(Puccinia graminis). The stem-rust superstrain Ug99 has
in recent years slashed yields in parts of Africa by as
much as 80%.

If all five crop staples were hit with fungal outbreaks
at the same time, more than 60% of the world's
population could go hungry, says Gurr. “That's
apocalyptic”, but unlikely, she says — “more of a James
Bond movie”. David Hughes, a zoologist at Pennsylvania
State University in University Park, adds that
terrorists could use fungi to wreak havoc by targeting
economically important crops. In the 1980s, for
example, a possibly deliberate infection wiped out
cacao crops in northern Brazil, changing the country's
demographics and ecology as people moved from
unproductive farms to the cities and cleared more
rainforest. “If you wanted to destabilize the world,
you could easily introduce rubber blight into southeast
Asia,” he says, which would trigger a chain reaction of
economic and political effects.

Modern agriculture has exacerbated societies'
vulnerability by encouraging farmers to plant the same
strains of high-yield crops, limiting the variety of
resistance genes among the plants, says Gurr. “We've
skewed the arms race in favour of the pathogen,” she
says. “That's why we're on the brink of disaster.”

Researchers estimate that there are 1.5 million to 5
million species of fungi in the world, but only 100,000
have been identified. Reports of new types of fungal
infection in plants and animals have risen nearly
tenfold since 1995 (ref. 3). Gurr suggests that climate
change might be a culprit.

Humans have cause for concern as well. In the past
decade, a tropical fungus called Cryptococcus gattii
has adapted to thrive in cooler climes and invaded the
forests of North America's Pacific Northwest. By 2010,
it had infected some 280 people, dozens of whom died.
Although fungi are not spread as easily from person to
person as viruses, for example, and anti-fungal agents
can effectively tackle most infections, there are still
reasons to worry. Fungi continue to evolve, and once
they are established in an ecosystem, they can be
almost impossible to wipe out.

Given these trends, experts say that fungi have not
received enough attention from researchers and
governments. “I'd be very surprised if an abrupt fungal
infection killed a large swathe of people. But it's not
impossible,” says Matthew Fisher, an emerging-disease
researcher at Imperial College London. “Complacency is
not a recommended course of action.”

Death from above

The heavens hold plenty of threats. The Sun
occasionally launches outsize solar flares, which fry
electricity grids by generating intense currents in
wires. The most recent solar megastorm, in 1859,
sparked fires in telegraph offices; today, a similarly
sized storm would knock out satellites and shut down
power grids for months or longer. That could cause
trillions of dollars in economic damage.

A solar flare some 20 times larger than that may have
hit Earth in 774, according to Adrian Melott, a
cosmologist at the University of Kansas in Lawrence,
and Brian Thomas, an astrophysicist at Washburn
University in Topeka, Kansas. “That's not an extinction
event,” says Melott, “but for a technological
civilization, it could kill hundreds of millions of
people and set us back 150 years.” Fortunately, there
are ways to mitigate this worst-case scenario should it
occur: engineers can protect the grid with fail-safes
or by turning off the power in the face of an incoming

Next up the scale of disaster magnitude is a large
comet or asteroid strike. Sixty-five million years ago,
an asteroid 10 kilometres wide hit Earth and triggered
the end-Cretaceous mass extinction; 2-kilometre rocks,
thought to be capable of causing extinctions on a
smaller scale, smack the planet once or twice every
million years. Astronomers are hard at work tallying
and tracking asteroids in Earth's vicinity, and
scientists are investigating ways to divert any real
threats that might materialize.

A far rarer danger — and one that could not be avoided
— is the blast of radiation from a nearby gamma-ray
burst. Perhaps the most frightening of these celestial
explosions is the 'short-hard' gamma-ray burst, caused
by the violent merger of two black holes, two neutron
stars or a combination. If one such blast were directed
at Earth from within 200 parsecs away (less than 1% of
the distance across the Milky Way), it would zap the
globe with enough high-energy photons to wipe out 30%
of the atmosphere's protective ozone layer for nearly a
decade5. That sort of event — expected once every 300
million years or so — would double the amount of
ultraviolet (UV) light reaching the ground and scorch
phytoplankton, which make up the base of the ocean's
food web.

Astronomers have no way of knowing whether such a rare
event is imminent. Neutron stars are small and dark, so
there is no catalogue of those within striking
distance. “We wouldn't see it coming,” says Thomas. In
as-yet-unpublished work, he estimates that such an
event could cause a 60% increase in UV damage to crops,
with up to 60% reduction in crop yields.

From a distance of about 2,000 parsecs, 'long-soft'
gamma-ray bursts — which result from the collapse of
massive stars — could also cause extinctions. But these
events are rarer than short-hard bursts, and easier to
spot in advance because they come from larger, brighter
stars. The two-star system WR 104 is some 2,500 parsecs
away from Earth, and is far enough along in its life
cycle that it is expected to explode some time in the
next few hundred thousand years — although the beam
from the burst is unlikely to hit Earth.

It is possible that a gamma-ray blast has hit the
planet before. Melott, Thomas and their colleagues have
suggested that the mass extinction at the end of the
Ordovician period, 440 million years ago, could have
been triggered by a gamma-ray blast that wiped out some
species through UV exposure and killed off others by
creating a sunlight-blocking haze of nitrogen dioxide6.
This would explain why some species went extinct before
the globe cooled during that period, and it fits the
extinction pattern, which shows that among marine
organisms, the greatest toll was on plankton and other
life in the upper part of the ocean.

Thomas says that none of these potential disasters is
keeping him up at night. He does, however, “have some
canned food in the basement” — a prudent backup in the
event of any disaster.

Death by water

Eight thousand years ago, sediments covering an
underwater area the size of Scotland slipped from their
moorings off the west coast of Norway and raced along
the sea floor. The Storegga slide triggered a tsunami
that ran at least 20 metres up the nearby Shetland
Islands, and probably wiped out some coastal tribes as
it clobbered shores around northern Europe. The scar it
left on the ocean floor stretches nearly 300
kilometres. “It's absolutely enormous, and I'm not
using the word 'enormous' lightly,” says Peter Talling,
a sedimentologist at the University of Southampton, UK,
who is leading a project to assess the country's risk
of similar slides.

The United Kingdom is not the only country concerned
about giant submarine landslides. “There are definitely
areas that have potential,” says Uri ten Brink, a
geophysicist at the US Geological Survey in Woods Hole,
Massachusetts, who conducted a 2008 study of possible
sources of tsunamis on the US east coast, where some
nuclear power plants are within striking distance of
such waves. “There are far larger piles of sediment
around today than Storegga ever was,” ten Brink says,
including deposits along the coast of southern Alaska
and off the Amazon, Niger and Nile river deltas.
Smaller slides are more probable and can still have a
huge local impact — and they often strike without
warning. In 1998, a relatively small (magnitude-7)
earthquake triggered an underwater slide that launched
a 15-metre-high tsunami into Papua New Guinea, killing
2,200 people.

Researchers say that it is hard to quantify the threat
of marine slides, particularly the giant ones. “There
is so little information about events that happen so
rarely,” says ten Brink. “We just have to learn as much
as we can.”

Nature 493, 154–156 (10 January 2013)

1 Mason, B. G., Pyle, D. M. & Oppenheimer, C. Bull.
Volcanol. 66, 735–748 (2004).

2 Isaia, R., Marianelli, P. & Sbrana, A. Geophys. Res.
Lett. 36, L21303 (2009).

3 Fisher, M. C. et al. Nature 484, 186–194 (2012).

4 Haas, B. J. et al. Nature 461, 393–398 (2009).

5 Melott, A. L. & Thomas, B. C. Astrobiology 11,
343–361 (2011).

6 Melott, A. L. et al. Int. J. Astrobiol. 3, 55–61


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