This is a wonderful tool and allows us to actually directly link real
activity deep down to events been experienced on the surface were
they could be measured. To start with, it clearly tells us that the
Mt St. Helen’s eruption was both inevitable and predictable at the
time had we had this knowledge.
At the time, I merely had to note that a half cubic mile of rock was
been lifted at the rate of six feet per day to know that the
potential energy been built up and would be released largely as
kinetic energy. I knew with that information that I wanted to be a
long ways away and the actual eruption was no surprise at all.
Most Volcanoes are not so generous in telegraphing their future,
although it is clear that the geological community has taken its
lesson and generally make sure quite early on that the surrounds are
evacuated.
The really good news here is that it is becoming feasible to map
movements and magnitudes within a magma chamber rather thoroughly and
we are reaching a point in which we can start tracking the volumes
necessary to trigger an actual eruption and to predict its ultimate
size and nature. This is excellent news and in the future, it will
become way more difficult to be surprised at all.
In truth, we have already saved thousands of lives and that can now
only become better.
Crystals reveal
inner workings of volcanoes
25 May 2012, by Tamera
Jones
Volcanologists have
found a direct link between swarms of earthquakes at the surface of
Mount St Helens in the US and injections of hot magma into its magma
chamber.
The findings bring
them a step closer to predicting when an explosive volcano like Mount
St Helens might next erupt.
The UK-led team of
researchers analysed tiny crystals in rocks erupted from the volcano.
These crystals contain a record of events inside the magma chamber
such as injections of hot magma or gas.
They found that
injections of magma or gas into the chamber from deep within the
Earth coincide with events at the surface, like swarms of
earthquakes, ground distortions, or releases of gas at the surface.
All are often a signal that the volcano is about to erupt.
'Now we have a
powerful tool that will let us work out how events at the surface
reflect what's going on inside the magma chamber,' says Dr Kate
Saunders from the University of Bristol, lead author of the study,
published in Science.
'Now we have a
powerful tool that will let us work out how events at the surface
reflect what's going on inside the magma chamber.'
Dr Kate Saunders, University of Bristol
Many volcanoes reveal
signs of an imminent eruption. Despite this, volcanologists have
struggled to understand how signals at the surface reflect what's
going on inside the magma chamber directly beneath the volcano.
Knowing what's happening below the surface is crucial for predicting
when an eruption is more likely.
Now, for the first
time, they have a tool that will help them read the signals, closing
the gap between observation and interpretation of restless volcanoes.
They used a fairly new
– and sophisticated – technique in volcanology, called diffusion
geochronology.
Most volcanic crystals
grow concentrically like tree rings, with zones which are made up of
different chemicals. Each new zone reflects subtle changes in the
pressure, heat or gas content of the magma it grew in.
So when hot magma is
injected from deep beneath the Earth's surface into the magma
chamber, a new zone is created in the crystals.
'The composition of
each zone is related to the composition of the magma around it when
it grew, so each zone acts like an archive of the crystal's growing
medium, or magma,' explains Professor Jon Blundy also from the
University of Bristol, co-author of the study. Once the crystals are
expelled as lava in an eruption, all growth stops.
But this is just
one aspect of diffusion chronology. Scientists can date the creation
of the zones - and therefore when each magma injection happened –
by the movement of trace elements between the zones.
Each element moves
at a specific speed. Magnesium for example moves at a rate of about
ten millionths of a metre per year.
If scientists know
how far an element like magnesium has moved, they can work out how
long ago a particular zone started growing.
'The movement of these
elements can tell us how long since a particular zone was grown.
Essentially the clock starts ticking when the new zone grows and
stops at the moment of eruption,' says Blundy.
So, say the movement
of magnesium tells them a new zone started growing five months ago,
and there were swarms of earthquakes at the same time, the
researchers can say that the two are linked.
Using this technique,
Saunders, Blundy and colleagues worked out how crystal growth relates
to events at the surface at Mount St Helens.
'We found a big
spurt of growth before the big 1980 eruption. And we've shown that
the process responsible for generating earthquakes at Mount St Helens
is pulsing of magma into the chamber,' says Saunders.
The researchers say
this technique could be applied to other volcanoes to understand how
events at the surface reflect changes inside the magma chamber, and
so reveal the inner workings of other explosive volcanoes.
Blundy says that
crystals could ultimately reveal clues about the size of the magma
chamber, as well as the conditions inside it.
'This technique
heralds real advances in our understanding of how volcanoes work,' he
says.
Kate Saunders, Jon
Blundy, Ralf Dohmen, Kathy Cashman, Linking Petrology and Seismology
at an Active Volcano, Science Vol. 336 no. 6084 pp.
1023-1027, published 25 May 2012, DOI: 10.1126/science.1220066
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