GPS Used To Predict Height of Volcanic Plumes

 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.

Original Article: Hreinsdóttir, Sigrún, Freysteinn Sigmundsson, Matthew J. Roberts, Halldór Björnsson, Ronni Grapenthin, Pórdur Arason, Thóra Árnadóttir et al. "Volcanic plume height correlated with magma-pressure change at Grimsvotn Volcano, Iceland." Nature Geoscience (2014).