Wicks uses data collected by the European Remote Sensing Satellite and employs a method called InSAR, or Interferometric Synthetic Aperture Radar. Interferometry is a technique of combining the input of two antennas (or telescopes) to effectively create one larger, higher resolution receiver that can measure the landscape to a precision less than the width of a ring finger.

More recently, in May of this year, Wicks saw an alarming batch of data while studying a region of Oregon called Three Sisters. A trio of ancient volcanic peaks dominates the landscape.

Wicks spotted a bulls-eye pattern in his topography data that showed the ground had risen as much as 4 inches (10 centimeters) over an area more than 9 miles (20 kilometers) in diameter sometime between August 1996 and October 2000.

He said the uplift, forced from below by rising magma, surprised him because the last eruption in the area was 1,500 years ago and there has been no earthquake activity that might hint at moving magma.

Whichever scenario unfolds, geologists will be watching from the ground.

The InSAR system cannot monitor all volcanic regions around the world all the time. But because of the early heads up it provided, a seismometer has been set up on the Three Sisters uplift to sense any possible earthquakes, and a GPS receiver now provides continuous monitoring of ground movement.

"InSAR tells people living around a dormant volcano that they need to keep a wary eye," Wicks said.

Satellite interferometry proved valuable beginning in the mid-1990s for the sort of work done in Oregon -- spotting land deformation across relatively large areas over weeks or months. In one early application, large-scale ground movements caused by the 1995 earthquake in Kobe, Japan, were studied by comparing an image fortuitously made more than a year before the earthquake with another produced just after.

But the technique is so sensitive that scientists discovered a curious flaw, one they are now turning to their advantage.

"It turns out the interferometry is messed up by small-scale changes on the surface," said Tom Farr, a geologist at NASA's Jet Propulsion Laboratory (JPL).

To spot ground deformation over time, a radar interferometer measures the same location of the Earth's surface on subsequent satellite orbits. But sometimes the radar is bounced off trees, instead of the ground. And researchers realized they sometimes accidentally measured the slight movement of a leaf on a tree, blowing in the wind.

"If the leaf is in a different position by a few centimeters, that's enough to mess it up," Farr said.

This flaw has been harnessed to model lava flows that "will spoil the data and it will pop right out of our measurements as a hot spot." Researchers at JPL are now working to create animations of lava flows by imaging a volcano with each satellite pass (24 hours with some systems).