False color image of zoned orthopyroxene crystal used in forensic-style analysis of Mount St Helens 1980 eruption. Image: Dr. Kate Saunders

A
forensic approach that links changes deep below a volcano to signals at
the surface is described by scientists from the University of Bristol
in a paper published recently in Science. The research could ultimately
help to predict future volcanic eruptions with greater accuracy.

Using
forensic-style chemical analysis, Dr. Kate Saunders and colleagues
directly linked seismic observations of the deadly 1980 Mount St. Helens
eruption to crystal growth within the magma chamber, the large
underground pool of liquid rock beneath the volcano.

Over
500 million people live close to volcanoes which may erupt with little
or no clear warning, causing widespread devastation, disruption to
aviation and even global effects on climate.  Many of the world’s
volcanoes are monitored for changes such as increases in seismicity or
ground deformation.  However, an on-going problem for volcanologists is
directly linking observations at the surface to processes occurring
underground.

Saunders
and colleagues studied zoned crystals, which grow concentrically like
tree rings within the magma body.  Individual zones have subtly
different chemical compositions, reflecting the changes in physical
conditions within the magma chamber and thus giving an indication of
volcanic processes and the timescales over which they occur.

Chemical
analysis of the crystals revealed evidence of pulses of magma into a
growing chamber within the volcano.  Peaks in crystal growth were found
to correlate with increased seismicity and gas emissions in the months
prior to the eruption.

Saunders
said: “Such a correlation between crystal growth and volcanic
seismicity has been long anticipated, but to see such clear evidence of
this relationship is remarkable.”

This
forensic approach can be applied to other active volcanoes to shed new
light upon the nature and timescale of pre-eruptive activity.  This will
help scientists to evaluate monitoring signals at restless volcanoes
and improve forecasting of future eruptions.

The research was funded by the Natural Environment Research Council (NERC).

Linking Petrology and Seismology at an Active Volcano

Source: University of Bristol