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| Photo of eruption Grímsvötn, May 2011. (SPR AFP/Getty Images) |
Scientists in Iceland have developed an innovative method to
predict volcanic plume height using changes in magma pressure. Using a series of anchored GPS stations, they
were able to detect inflation of the Grímsvötn volcano before its eruption in
May 2011 and the sudden co-eruptive subsidence.
These GPS stations, originally installed to monitor the
movement of tectonic plates over time, continuously recorded position and
elevation during the pre-eruptive and eruptive phases of the explosion. They found that the volcano expanded radially
approximately 20 inches in the hour preceding the eruption and sank 10 inches
during the initial eruptive phase, resulting in tilting of one hundredth of a
degree. By tracking the change in volume
of the volcano, the scientists were able to track the change in pressure of the
magma chamber during the eruption. This
process is similar to a tire deflating – as air (or in the case of a volcano,
magma) leaks out the tire pressure decreases.
Based off this change in pressure, the total change in
volume of the magma chamber was .027 km3, about 10x smaller than the total
erupted volume. Pumice is extremely porous and can contain over 50% void space;
this is a result of bubbles being trapped in the solidifying melt as they
expand due to decreased pressure at the volcanic vent relative to the magma
chamber. The scientists were then able to determine the rate of the eruption
using the overall duration and amount of ejected material. The mass eruption rate is directly correlated
with the height of the plume; the faster the eruption rate, the taller the
plume. Using this novel method, they estimated that the plume height peaked at
15 km, which compares favorably to satellite imagery.
Column height is an important parameter to predict where an
ash cloud will travel. The heat produced
by jet engines cause the ash particles to melt, gunking up the engine and
causing the plane to stall. Currently,
the protocol for avoiding this is to completely close airspace. The eruption of Grímsvötn, which lasted for
seven days, caused airspace closures in northern Europe, grounding
approximately 900 flights. Better
predictions of column height would result in more accurate hazard maps and
fewer plane delays. This new method to estimate plume height uses real time
data that does not rely on satellites.
Aviation experts can then better seed their models to create smaller no
fly zones due to more accurate predictions of ash movement.
