expect more potentially deadly avalanches to come, and also more
frequent, and fiercer, volcanic eruption and earthquakes.
On the night of 13 December 1991, a group of climbers had gathered in a hut
on New Zealand's highest peak, Mount Cook, in preparation for an attempt on
the summit. The ascent would mean risking their lives, but that threat was
nothing compared with what was about to come. Shortly after midnight, 12
million cubic metres of rock and ice crumbled from the peak and roared down
the east face of the mountain, travelling at over 200 km per hour for more
than seven kilometres before plunging to the valley floor. The cataclysmic
rock avalanche narrowly missed the hut, leaving the stunned climbers safe,
but awed. "Essentially, the top of Mount cook fell off - which is
incredible," a mountaineer told TVNZ at the time. The group had a very lucky
escape from what on the face of it was an act of God - a purely natural
But was it? A few analysis suggests that climate change may have helped to
trigger this avalanche, as well as others in different parts of the world.
given current projections of even warmer temperatures into the future, some
scientists are now warning that we should expect more potentially deadly
avalanches to come, and also more frequent, and fiercer, volcanic eruptions
Until recently, the idea that current and future climate change could ramp
up these sorts of geological hazards wasn't well appreciated. Climate
scientists have until now been focussing on the atmosphere and the
hydrosphere, most probably because those are the primary areas of interest
for most of them. Now Earth scientists are starting to become involved in
the study of future climate impacts - and they are bringing with them a
knowledge of how past climate change has triggered a response from the
Earth's crust. Scientists led the new work on the 1991 Mount Cook avalanche,
and on four others that happened recently in Alaska and the European Alps.
The scientists painstakingly analysed the meteorological conditions in the
weeks leading up to the disasters and found that all had one thing in
common: each of the avalanches was preceded by an unusually warm period.
For Mount Cook, between 1960 and 1990, the average year-round air
temperature at the summit was -7.87 deg C. In 1991, the winter was
particularly cold, then, in November and December, the summit temperature
regularly rose above zero. Next came a cooling, which brought temperatures
to below seasonal averages. But in the week immediately before the
avalanche, the summit warmed again, with temperatures on December 11 soaring
to 9.7 deg - about 8.5 deg C above the long-term average for that
date. The ice on the summit began to melt in earnest. Then 24 hours before
the avalanche, the temperature plummeted below freezing. The unusually warm
conditions melted more snow and ice than normal, causing relatively large
amounts of water to leak through clefts and joints into the rock.
Then the plunge in temperature suddenly froze this water, making it swell
and forcing some of the rock to break away. The team also analysed
avalanches and landslides on Mount Steller in Alaska in 2005 and 2008, and
on Mount Miller, also in Alaska, in 2008, and on Mount Miller, also in
Alaska, in 2008, as well as on Monte Rosa in the Swiss Alps, in 2005 and
2007. They found that while the precise temperature patterns before each
event varied, the weeks or days before were unusually warm.
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Several studies have found that during the 20th century, there have been
more unusually warm periods, such as summer heat waves. In the past two to
three decades, there has also been an increase in the number of large
avalanches and landslides in some high-altitude regions, such as the peaks
of the European Alps. They can never say that a particular event would not
have happened even without global warming but the rising incidence of large
rock and ice avalanches in Alaska and the Caucasus, together with an
increase in rock-falls in the alps and elsewhere, is just what would be
expected to be seen as the world warms. Since climate models suggest that
warmer periods will become up to four times more common in the next several
decades, this means we are likely to experience more avalanches. The main
concern is very large events - like those in Alaska - will occur in more
populated regions, like the Swiss Alps and it is rather likely that the
probability for this will increase - but we cannot quantify it. Mountain
regions are particularly sensitive to climate change because melting snow
means less heat is reflected back towards space and more is absorbed. In
fact, temperatures in the European Alps have been rising at double the rate
of the global average since the late 19th century. Recent studies show that
the permafrost in the European Alps has warmed by between o.5 and 0.8 deg C
in the upper tens of metres during the 20th century.
Scientists and researchers have also studied avalanches, as well as
rock-falls, landslides and floods in the European Alps during the 2003
heatwave - when temperatures in Central Europe were the hottest in 500 years
- and 2005 summer floods, which caused the most catastrophic flood damage in
the region in the last 100 years, battering central and eastern parts of the
continent and closing many mountain passes in Switzerland and Austria.
During the 2003 heatwave, the tem found permafrost and warmed even in high
alpine areas, weakening the rock, and helping to trigger rock-falls and
landslides, including a large rockfall on the iconic Matterhorn in
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is tricky to use climate models to predict what will happen to mountain
hazards, partly because the models don't work well for regions with big
surface feature variations - such as mountain ranges - but warming
permafrost seems very likely to mean more landslides, and what we do know is
that landslides and related creatures, such as debris flows, usually start
at the interface between 'warm' and 'cold' permafrost. As the area of 'warm'
permafrost spreads, so will the places where the landslides are triggered.
This response will play out over the coming decades. But if warmer
temperatures increase the risk of avalanches, landslides and rockfalls, they
may also boost the chances of another potential catastrophe: earthquakes.
There is compelling evidence that melting of ice during the last de-glaciation
triggered a burst in volcanic activity.
STEP BACK IN TIME
9,000 years, and the
geological record shows that Scandinavia was experiencing a flurry of
earthquakes. Yet today, there are few. Researchers wondered why. When they
looked into past conditions in the region, it was realised that the surge in
quakes coincided with the melting of a massive ice sheet that had covered
the area during the last ice age. Suspecting a link, a team of researchers
used a computer model to investigate what being buried under several hundred
metres of ice can do to geological faults. They found that a massive weight
of ice can stop these faults from slipping, and so keep a lid of quakes. But
the stresses in the ground continue to build up. When warming temperatures
cause the ice to melt, the pent-up energy is released, unleasing stronger
quakes, and more of them. Historicala records from some other regions of the
world, such as the Yellowstone ice cap in the U.S., show a similar pattern
to that in Scandinavia - large ice caps, glaciers and even lakes can
suppress quakes, but if this weight vanishes, there's s surge in them. The
idea that melting glaciers have altered the pattern of physical load on the
planet - reducing it where the ice has melted, and increasing it where the
sea level rises - and that this might influence earthquake activity is a
reasonable one. The idea is that the same thing will happen with climate
change resulting in removing loads from glaciers and adding load to the
ocean. And that's a reasonable thing to propose.
glacier-covered summit of Mount Cook, New Zealand, in 2006
Many glaciers around the world are now receding. By 2000, the alpine
glaciers shrank to almost half their volume compared with 1850, In January
2010, a report was published saying that glaciers around the world are
melting so fast that many will be gone by the middle of this century. The
latest date for 2007-2008 on 96 glaciers found that, on average, they
thinned by nearly half a metre. The most vulnerable are those in lower
mountain ranges, including the Alps, Pyrenees, North American Rockies and
parts of the Andes. It's difficult to predict, though, what the removal of a
given weight of ice will do to earthquake activity in various parts of the
world in the future. Although evidence of large earthquakes associated with
the Late Pleistocene de-glaciation wee found in Scandinavia, evidence of
only small and moderate earthquakes were found in northern Canada, where the
ice changes were even larger. However, there is evidence that climate change
may already be triggering earthquakes in Alaska.
Alaska is a great place to look for evidence linking melting glaciers to
earthquakes, because the ice cap is directly above a shallow quake zone,
caused by the movement of the pacific-Yakutat plate beneath continental
Alaska. The frequency of small quakes in the Icy Bay region increased
between 2002 and 2006, compared with the recent past - and they suggest that
this is down to a significant increase in ice loss in that period. Warming
temperatures might also mean more quakes for Greenland and Antarctica, the
models suggest that the massive ice sheets in these regions are suppressing
local seismic activity. But they are melting. According to a study by a tem
at the University of California, for example, different glaciers in
Greenland are losing between 0.7 and 3.9 metres of ice each day from
underneath. This means we could see more small quakes in these two regions
as soon as in the next 10 to 100 years. And melting glaciers seem likely to
trigger yet another, perhaps even more surprising, danger: more, and more
explosive, volcanic eruptions. About 130 km west of Bogota, in Colombia,
lies the Nevado del Ruiz volcano. It's the northernmost volcano in a group
known as the Andean volcanic Belt, which forms part of the notorious Pacific
Ring of Fire.
13 November 1985, Nevado del Ruiz erupted. It was relatively small, as
eruptions go, scoring only three out of eight on the volcanic Explosivity
Index. But it unleashed four deadly lahars - mixtures of mud and debris -
that careened down the sides of the mountain. They buried the town of Armero
and struck the town of Chinchina, killing more than 23,000 people in total,
and going down as one of the deadliest in history.
have to face the fact that unmitigated climate change is going to be
summit of Nevado de Ruiz, like those of the other mountains in the Los
Nevados Natural National Park, is topped by large glaciers. A hundred years
ago, the ice covered an area of about 100 km. By the end of the 1950s,
warmer air temperatures had reduced it to about 34 km. Could the melting ice
have had anything to do with the eruption? Some scientists think it is
possible - and that melting glaciers could boost volcanic activity in other
regions too. As with earthquakes, there is a good historical basis for the
suspicion. Jump back once more to the end of the last ice age, and to
Iceland. The island lies along the Mid-Atlantic Ridge, where the North
American tectonic plate and the Eurasian plate are diverging from each
other. This causes hot rock to well up from deep within the planet,
triggering melting in the mantle region and eruptions at the surface. Work
published in 2005 shows that as the country's vast glaciers melted, there
were 10 times as many volcanic eruptions as there are today.
Since 1890, Iceland's glaciers, which cover parts of this ridge, have been
thinning. Some researchers argue that, based on the historical data, the
country is heading towards another period of devastating eruptions. And
Freysteinn Sigmundsson of the Nordic Volcanological Centre at the University
of Iceland thinks he can explain why. Sigmundsson and his colleagues have
created a model of what would happen to the production of magma if the ice
on top of an Icelandic volcano melted. This would reduce the downwards
pressure and so, they think, increase the upwelling of molten rock towards
the surface, making eruptions more frequent and more explosive. The team has
looked closely at the Vatnajokull glacier, the largest in Iceland, covering
8% of the country. The ice cap is receding at a rate of about 50 cm per
year, which, according to their model, will relieve enough pressure to
generate significantly more magma. And this, they say, should lead to more
frequent, or bigger, eruptions.
2010 eruptions of Eyjafjallajokull are very unlikely to be linked to climate
change, however, the team adds, as their model suggests that extra magma
produced as a result of warmer temperatures is likely to take anywhere
between decades and centuries to reach the surface. In the Andes, too, it's
thought likely that the melting of ice caps will increase volcanic activity.
At least, the geological date suggests that this is what happened in the
past, and it may be happening again. The U.S. Geological Survey Team pointed
out in a paper published back in 1990, the deadly 1985 eruption of Nevado
del Ruiz followed a loss of covering ice, and the same is true for other
recent eruptions, like that of Villarrica in Chile in 1971, which released
large mudflows caused by lava melting ice.
heavily damaged school in Yingxiu, China,
where 80% of the town was destroyed by the 12 May 2008 earthquake.
melting ice doesn't have to increase the chance of an eruption to make a
volcano more deadly. Researchers have also recently studied Italy's Mount
Etna, the largest active volcano in Europe, and one of the most active in
the world. since historical records began, a massive five by eight kilometre
portion of the volcano's eastern flank has been missing. Based on their
analysis of samples from the site, the team concludes that this portion
collapsed 7,500 years ago, when the climate became wetter, as well as
warmer. They think that heavy rainfall destabilised the structure of the
volcano, triggering its partial disintegration. And some regions of the
world, including the eastern parts of South America, are predicted to get
even wetter as a result of climate change.
THANKFULLY, SUCH AN EXTREME scenario isn't likely. While the historical data
can help us understand what might happen in the future, the end of the last
ice age involved a much more serious change in climate than is predicted
now. The de-glaciation after the last ice age involved a very substantial
change in load. Back then, the glaciers were kilometres thick, and the
global sea rise associated with their melting was a little over 100m.
Whereas with climate change, we're talking about glaciers that aren't as big
and a change in global sea level of about one metre. So while a statistical
increase in quake activity is very possible, it would be a surprise if we
saw a very large increase in large quakes.
While there may be an increase in small quakes, large quakes which pose most
risk to people, will still be caused by natural movement of tectonic plates.
Glaciers and ice sheets on many active volcanoes are rapidly receding. And
there is compelling evidence that melting of ice during the last de-glaciation
triggered a burst in volcanic activity. Ice melting was massive, and it is
very hard to know exactly how current climate change, and predicted ice
melting, will affect the planet's volcanoes - and when. Researchers' model
cannot yet reveal how quickly volcanoes will react to melting ice, or
whether they're sensitive to small changes in ice thickness, or not. There
is a strong potential for melting ice to increase volcanism - but much more
research to better understand this is now needed.
More volcanic eruptions could also act against climate change. Major
eruptions cause a local cooling in air temperatures, as the ash clouds block
incoming heat from the sun. Indeed, mimicking a volcanic eruption by
injecting sulphate particles into the atmosphere is one idea for 'geoengineering'
our way out of deleterious climate change. So quite how these two processes
will interact is not clear. Ultimately, an increase in volcanic activity
could actually act to cool the planet - at least for a time. some climate
scientists have been accused of disaster-mongering, and that critics may put
the work on geohazards into that category.
But the risks are real that a
balance has to be struck between informing people and scaremongering. We
have to face the fact that unmitigated climate change is going to be
catastrophic - and that the Earth's crust will certainly become a source of
increased hazardous activity. The bottom line remains that global greenhouse
gas emissions must now be reduced. If they are not stablised within five
years or so - and the prospects for this do not look that bright - it will
be almost impossible to avoid all-pervasive, devastating climate change.
This will mean that we need to tackle the resulting geohazards as they
occur, using a combination of education, risk communication, land-use
planning - and engineering solutions.
Deep beneath the oceans lie monumental deposits of methane, a potent
greenhouse gas. The methane is trapped in ice, and no one is sure exactly
how much is down there - but about 2,000 gigatonnes of carbon (almost three
times the amount of carbon in the atmosphere) could be stored in this form.
warming oceans could release some of this carbon, speeding climate change
and also destabilising the ocean floor, potentially unleashing tsunamis.
global warming of 3 deg C could release about 900 gigatonnes of carbon from
these 'gas hydrate' deposits, adding 0.5 deg C to air temperatures. But
about 400 gigatonnes of carbon is also stored in methane trapped in
permafrost - and temperature increases of more than 12 deg C are predicted
for permafrost regions of North America and north Asia. Already, 100 times
more methane than normal is being released from some regions of the Siberian
Arctic, according to work published in 2008. Rising temperatures will also
release methane from peatlands, though just how much is not yet clear. This
is one of the greatest uncertainties in carbon cycle science. Thawing
permafrost generally releases methane from surface soils. But if that
thawing of permafrost also exposes deeper gas hydrates to release, we have a
much more serious problem in terms of greenhouse gas emissions. The tsunami
risk comes if gas hydrates below the ocean floor break down. These deposits
can act like cement for the sediment, and if they fail, there could be
massive underwater landslides.
But plumes of methane gas bubbles rising from the sea floor to the surface
could pose other threats. If enough methane is released in relatively
shallow water, it could cause ships to lose their buoyancy, and to flounder.
of the 2004
Boxing Day Asian Tsunami captured from the balcony of the Sheraton
Grande Laguna Resort on Phuket Island, Thailand. The tsunami
resulted in the deaths of 225,000 people (see below).