GPS watches Mount St. Helens

Even as Mount St. Helens threatens to erupt, scientists are planning a network of Global Positioning System receivers to map the volcano's movement and help predict the likelihood of an eruption. The network would also help predict earthquakes throughout North America.

A crew of three people is installing two Global Positioning System stations around the volcano, as part of EarthScope. A week from today, they will deploy five GPS instruments. A team has performed helicopter reconnaissance to scout the area, said Michael Jackson, plate boundary observatory director at Unavco Inc., a nonprofit group that promotes high-precision geodetic and strain techniques such as GPS.

"We're working to get at least five stations installed within the next week, but we haven't gotten it approved yet," Jackson said last week.

The GPS system will consume about half of the budget for the $200 million EarthScope project. The undertaking will measure latitude and longitude at 875 permanent GPS stations, graphing how the earth moves over time. Each receiver can measure relative distance changes of less than 0.5 millimeters.

The network of receivers, called the Plate Boundary Observatory, is a project of both the National Science Foundation and the U.S. Geological Survey.

Two telemetered microphones are now in operation to detect explosions. USGS will receive a remotely operated video camera that will be installed on the crater rim from the USGS Hawaiian Volcano Observatory, and field crews will work to install additional seismometers on the flanks of the volcano, continuing to harden the GPS sites and download data.