Rock Doc

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 of 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 2010 eruption -- from the Eyjafjallajökull volcano -- grounded many flights across northern Europe and made major headlines at the time.

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.

Data from "a GPS site 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," said Sigrún Hreinsdóttir, speaking to Nature Geoscience. Hreinsdóttir is a geophysicist at the University of Iceland and 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 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. Such pressure tends to correspond to the size of the eventual ash plume.

It's long been the case that seismic instruments have 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 to come, Hreinsdóttir explained.

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

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

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