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Weatherwatch:
Extreme weather dwarfed by impact of volcanic eruption
Paul
Brown
4
November, 2012
A
drop in crop yields in the UK and many other grain producing
countries, as a result of extreme weather, has increased prices
worldwide, and may cause serious hardship. But these consequences
would be dwarfed by the catastrophe that a volcano could unleash on a
heavily populated planet.
Evidence
unearthed in London's Spitalfields of mass graves, dated to 1258,
shows that between 20 and 40 bodies were buried at once in a series
of pits in the cemetery. There were both sexes, with adults and
children together. They are believed to be famine victims because
they had no battle injuries and it was a century before the Black
Death.
The
same year the monk Matthew Paris of St Albans recorded "unendurable
cold" in the winter that suspended all cultivation and killed
calves. In June spring had still not arrived and wheat was so scarce
that "a very large number of poor people died."
Contemporary
chroniclers in other continents also record appalling weather and
mass starvation. Geologists have found that over both hemispheres, as
far south as Antarctica, there is a thick layer of volcanic ash from
the same period. The sheer quantity of aerosols projected into the
atmosphere would have blotted out the sun and wiped out crops. The
volcano responsible for this devastation and mass starvation is not
known, but 850 years is a short gap in geological time. Somewhere
this monster is dormant and could erupt again.
Ancient
Supervolcano Affected the Ends of the Earth
5
November, 2012
About
74,000 years ago, the Toba volcano on the Indonesian island of
Sumatra erupted with catastrophic force. Estimated to be 5,000 times
larger than the 1980 eruption of Mount St. Helens, it is believed to
be the largest volcanic event on Earth in the last 2 million years.
Toba
spewed enough lava to build two Mount Everests, it produced huge
clouds of ash that blocked sunlight for years, and it the left behind
a crater 31 miles (50 kilometers) across. The volcano even sent
enough sulphuric acid into the atmosphere to create acid rain
downpours in the Earth's polar regions, which researchers have found
evidence of in deep ice cores.
"We
have now traced this acid rain in the ice caps on Greenland and
Antarctica," glaciologist Anders Svensson, of the Niels Bohr
Institute at the University of Copenhagen, said in a statement.
"We
have long had an idea of at what depth the Toba eruption could be
found in the Greenland ice cap, but we found no ash, so we could not
be sure," Svensson added. "But now we have found the same
series of acid layers from Toba in the Greenland ice sheet and in the
ice cap in Antarctica. We have counted the annual layers between acid
peaks in ice cores from the two ice caps and it fits together."
The
ice cores could offer more evidence about how the changed Earth's
climate was drastically changed in the years after the colossal
eruption. Researchers had previously estimated that such an event
would have prompted a cooling of up to 10 degrees C (18 degrees F) in
the global temperature for decades, but the ice cores show the
cooling was probably short and not consistent across the globe.
"In
the temperature curves from the ice cores we can see that there is no
general global cooling as a result of the eruption," Svensson
said. "There is certainly a cooling and large fluctuations in
temperature in the Northern Hemisphere, but it becomes warmer in the
Southern Hemisphere, so the global cooling has been short."
The
new evidence also promises to settle some archaeological debates. The
Toba eruption occurred at a critical point in early human history
when Homo sapiens were first venturing out of Africa into Asia.
However, there is wide disagreement about how early human were
affected and whether large parts of the population were wiped out by
the blast.
Layers
of ash from the Toba eruption have been found in Asia and serve as a
very important reference horizon for ancient archaeological clues
from this period that are too old to be carbon dated. The ice cores
now provide another backdrop against which to place ancient finds.
"The
new precise location of the Toba eruption in the ice cores will place
the archaeological finds in a climatic context, which will help to
shed light on this critical period of human history," Svensson
said.
The
study is detailed in the journal Climate of the Past.
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