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May 18th, 2015 
David Schulberg 
Just a small variation in external noise can produce the earthquakes that accompany volcanic eruptions, such as those seen at Calbuco in Chile last month, Russian scientists have discovered.
Certain volcanic
eruptions, such the one at Mount St. Helens in Washington State
in 2004 -2005, which the authors from the Ural Federal University
in Yekaterinburg studied, are marked by a regular drumbeat of
small earthquakes. In Calbuco last month, there were scores of
tremblers of up to 3.6 in magnitude before the volcano finally
exploded.
However, why this occurs is poorly understood.
“Volcanoes are considered chaotic systems. They are difficult
to model because the geophysical and chemical parameters in
volcanic eruptions exhibit high levels of uncertainty,”
admits a statement from the Yekaterinburg team, which has
published its findings in The European Physical Journal B.
Unable to reach inside the volcano itself, volcanologists believe
these precursor earthquakes are caused by a phenomenon known as
stick-slip behavior. Imagine dragging a heavy box along a rugged
surface by an elastic cord – as you pull, the cord stretches, but
the box does not move until the cord reaches a certain level of
tension, after which the box suddenly jerks free and moves. To
force the box further, this process would be repeated.
The same motion could be happening inside the volcano, with the
magma rising from the depths pushing the volcanic plug up in
these stutter steps, moving it by perhaps less than 0.5
centimeters each time.
The Yekaterinburg team decided to test a mathematical model of
this stick-slip motion, but also added another factor – outside
noise projected onto the volcano.
What they found was revealing – not only did the noise contribute
to the oscillations, but relatively small sound waves could
produce a disproportionate destabilizing effect, with the volcano
seeming to dance to the beat of the white noise coming in from
outside.
The team now hopes to apply their findings in a practical area –
forecasting eruptions, by understanding the mechanisms within
volcanoes. They admit, however, there are still too many
variables to be able to use mathematical models like theirs to
predict real eruptions.
“Predicting when, where and how volcanic eruptions will
happen is likely to remain empirical. That is, until it is
possible to improve the modeling of their dynamics. The challenge
of such models is that the volcanic eruption dynamics are very
complex, involving simultaneous unrelated processes and offering
a variety of possible scenarios,” the Yekaterinburg
volcanologists said in their statement.
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‘Drumbeat’ volcano earthquakes triggered by external noise – study
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