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Monday, October 19, 2020  Spokane, Washington  Est. May 19, 1883
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Rock Doc: GPS monitors help scientists predict volcanic eruptions

E. Kirsten Peters

There are two main things most people would like to know about particular volcanoes: When is the next eruption and how big will that eruption be? Scientists in Iceland have taken another step forward in monitoring volcanoes to best predict when they will erupt and even warn people of the size of the coming eruption.

In May 2011, a volcano in Iceland named Grímsvötn erupted. It generated a 12-mile-high plume of volcanic debris that temporarily grounded airplanes as far away as Great Britain. The problem wasn’t as great, though, as that which had occurred a year earlier, when another Icelandic volcano erupted. That eruption – from the Eyjafjallajökull volcano – grounded many flights across northern Europe and made headlines.

The 2011 Grímsvötn eruption was recently written up in the journal Nature Geoscience to illustrate an advance researchers made that may help us with future predictions of volcanic activity. Because scientists knew the volcano was coming to life, they had placed a Global Positioning System monitor on its flank.

About an hour before Grímsvötn erupted, the GPS device – rigged to send readings to scientists in real time – registered ground movement of a couple of feet. GPS data “can tell you not only that there’s unrest at a volcano, but that it’s about to erupt and then how high its plume will be,” Sigrún Hreinsdóttir told Nature Geoscience. Hreinsdóttir, a geophysicist at the University of Iceland, is one of the authors of the journal article.

Obviously, the more information that can be known, the better, when it comes to eruptions. Any information about timing can help people evacuate the areas likely to be affected. And knowing how high the volcanic plume may reach can help pilots and air traffic controllers as they try to adapt to a situation that’s rapidly unfolding.

Grímsvötn is an active volcano, so inquiring minds may want to know why it’s not thoroughly covered in GPS monitors. The answer is that much of the volcano lies beneath an ice sheet. Ice sheets have their own movement issues, so monitoring them won’t give you good information about a volcano.  Researchers did what they could to attach a GPS device on a rare rocky outcrop above the ice.

Next came a bit of math. The researchers didn’t want to just record ground movement, they wanted to estimate what they could about what such movement meant for changes in pressure in the underground magma chamber, which tends to correspond to the size of the eventual ash plume.

Seismic instruments have long been used to monitor tremors and give general predictions of when an eruption will occur. But the GPS measurements have the advantage of giving information about the size of the eruption, Hreinsdóttir said.

The new GPS approach with the magma-pressure calculations still needs further testing.

“We need another eruption to prove we are right,” Hreinsdóttir said.

E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard universities. This column is a service of the College of Agricultural, Human, and Natural Resource Sciences at Washington State University. 
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