Volcano monitoring will take an important step toward better science and improved safety this week when researchers publish satellite data showing that four volcanoes in South America are not dormant, as thought, but are active.
In tomorrow's issue of the journal Nature, Caltech graduate student Matthew Pritchard and his faculty adviser, Mark Simons, will detail evidence of subtle ground deformation they've noted on four Andean volcanoes. The researchers made no predictions about any imminent eruptions.
The study involved eight years of data collected on 900 volcanic mountains using the European Space Agency's ERS 1 and ERS 2 satellites.
In some cases, the ground is rising about a half-inch per year (1-2 centimeters). On one mountain, the ground is sinking for unknown reasons. Such changes hint at magma -- the stuff that becomes lava if it reaches the surface -- welling up and moving around underground.
Interestingly, of the 50 volcanoes in the study that had previously been classified as potentially active, none showed ground movement.
Years and even centuries can pass between subsequent eruptions of a particular volcano, and scientists have struggled in recent years to develop better monitoring techniques, though predicting eruptions is still an inexact science. Ground movement has become one fairly reliable indicator of potential surface activity, from catastrophic localized mudslides to full-blown eruptions of lava and ash.
While the new study could help geologists warn of future eruptions, it is perhaps more important for the fact that it proves the mettle of a relatively new, sensitive and comprehensive method for finding active volcanoes, which scientists can then target for detailed ground-based studies that might include sniffing for telltale chemical signatures of impending danger.
Until recently, geologists who monitor ground swells have relied mostly on the Global Positioning System (GPS), a collection of satellites that depend on a ground-based device to generate highly precise altitude and position readings for a single spot.
With the new method, called interferometry, satellites bounce a radar signal off the ground, then measure the time it takes the signal to return. On another orbit when the satellite is in the same location -- days or even years later - it repeats the process.
Any change in the time the signal takes to go down and back indicates ground motion. Unlike GPS, however, satellite interferometry can map an entire region, generating maps that show change over time.
"You can think of a magma chamber as a balloon beneath the surface inflating and deflating," Pritchard said. "So if the magma is building up underground, you expect a swelling upward, and this is what we can detect with the satellite data."
The researchers say that with a new generation of satellites in the right orbits, all the world's volcanoes -- except those under the sea surface -- could be monitored weekly, which "would have a profound impact on minimizing volcanic hazards."
A constellation of three or four satellites could do this and more, Simons told SPACE.com, monitoring the creep of glaciers and even noting minor ground migration over long periods of time that could help scientists spot locations ripe for earthquakes.
"We could revolutionize solid Earth geophysics and glaciology," Simons said.
The data analysis was done with software developed at Caltech and the Jet Propulsion Laboratory, which is operated by Caltech for NASA.
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