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The largest volcanoes on Earth may take as little as
a few hundred years to form and erupt, a new study has revealed.
These supervolcanoes were thought to exist for as much as 200,000 years
before releasing their vast underground pools of molten rock.
Researchers have sampled the rock at the supervolcano site of Long
Valley in California.
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Their findings suggest that the magma pool beneath it erupted within as
little as hundreds of years of forming.
That eruption is estimated to have happened about 760,000 years ago, and
would have covered half of North America in its ash.
Such super-eruptions can release thousands of cubic kilometres of debris
- hundreds of times larger than any eruption seen in the history of
humanity.
Eruptions on this scale could release enough ash to influence the global
weather for years, and one theory holds that the Lake Toba eruption in
Indonesia about 70,000 years ago had long-term effects that nearly wiped
out humans altogether.
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What little is known about the formation of these supervolcanoes is
largely based on the study of crystals of a material called zircon,
which contains small amounts of radioactive elements whose age can be
estimated using the same techniques used to date archaeological
artefacts and dinosaur bones.
Zircon studies to date have suggested that the time between the
formation of the enormous magma pools and the eventual super-eruptions
can be measured in the hundreds of thousands of years.
Now, Guilherme Gualda of Vanderbilt University and his colleagues
present several lines of evidence from the Bishop Tuff deposit at Long
Valley, suggesting that the pools are “ephemeral” - lasting as little as
500 years before eruption.
Initially, the magma pools are nearly purely liquid rock, with few
bubbles or re-crystallised minerals.
Over time, crystals develop, but the process stops at the point of the
eruption. As a result, the characteristic development time of these
crystals can also give an estimate of how long a magma pool existed
before erupting.
Rather than zircon, the team’s target was crystals of the common mineral
quartz.
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Since the processes and timescales of quartz formation in the
extraordinary underground conditions of a magma pool are well-known, the
team was able to determine how long the crystals were forming within
Long Valley’s supervolcano before being spewed out in the eruption.
Their estimates suggest the quartz formed over a range of time between
500 and 3,000 years.
“Our study suggests that when these exceptionally large magma pools form
they are ephemeral and cannot exist very long without erupting,” the BBC
quoted Gualda as saying.
“The fact that the process of magma body formation occurs in historical
time, instead of geological time, completely changes the nature of the
problem,” Gualda said,
The study has been published in Plos One. |