In a development that could ultimately make life safer for some of the estimated 500 million people worldwide who live on or near volcanoes, an international collaboration of scientists has developed an instrument to monitor Earth's geology from space.

The Japanese-built ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) is one of five instruments that will fly on EOS AM-1, an American satellite scheduled to launch in June 1998 as part of NASA's Earth Observing System.

During its five-year mission, ASTER will collect thermal infrared data for Earth's entire land surface. Researchers will use the data--gathered at two-week intervals--to track changes to surface features such as volcanoes.

"Most volcanoes in places like South American and Indonesia sit there for 200, 300 years," said Michael S. Ramsey, a geologist at Arizona State University. "People know they're living on a volcano, but it's a tropical jungle. Then all of a sudden one day BOOM! the thing blows up and 20,000 people die.

"That's where spaceborne monitoring helps. You can watch volcanoes and at least maybe have some kind of day, week, two-week warning that something's going on there--get people to move."

Most geologists track changes over years. ASTER could make things faster by providing data to researchers in days, not decades.

"For things like deserts and volcanoes and glaciers, which move in the span of a year or a season, speed becomes important," Ramsey said. "If there's an eruption in progress, or say a Mount Saint Helens starts to heat up, then we want data as quickly as we can get it."

Working with ASU geology professor and ASTER team member Philip R. Christensen, who is in charge of a similar instrument that will start mapping Mars in November, Ramsey has developed a computer model that enables scientists to create and study thermal infrared maps of lava flows. The idea is to reconstruct a volcano's past with an eye toward predicting its future.

By looking at how bubbly the volcanic rock is--its vesicularity--researchers can learn how much gas was dissolved in the lava when it erupted. This provides clues about how explosive the eruption may have been--and may be again.

Ramsey will present his research May 21 at a meeting of the Geological Society of America in Kailua-Kona, Hawaii.

"There are a lot of potentially dangerous volcanoes that are not easily accessible and are not regularly monitored," said Jonathan H. Fink, chairman of ASU's geology department and co-author of the research paper.

Ramsey has successfully used his computer model to study recently active volcanic domes in northern California. "You get on top of one of these things, and it's just this never-ending sea of boulders and glass," he said. "It's very interesting, but there's no real way to walk across this stuff and actually take samples and see what's going on.

"So the idea was, let's use thermal infrared to try to map the minerals and glass there. Every mineral on Earth has a fingerprint."

In the next two weeks, Ramsey hopes to confirm that his model applies equally well to the steadier, more fluid basaltic lava flows of Kilauea.

Since 1982 researchers have sporadically used instruments on airplanes to gather high-resolution thermal infrared data about Kilauea. But the ASTER instrument will mark the first time such remote sensing will be done from space. The advantages of spaceborne sensing include greater convenience and less cost, plus greater aerial coverage and frequency of monitoring, Fink said.

Lava domes remain the volcanoes to keep an eye on, he said. "Those kinds of lavas tend to be associated more with explosions--very violent explosions."

How violent?

"When a dome collapses, it may generate what's called a pyroclastic flow, which is a very deadly thing," Fink said. "The movie Dante's Peak has a pretty graphically simulated one. These are fiery clouds of gas and ash and chunks of rock that can move hundreds of miles an hour and be up to 500 degrees centigrade. They basically incinerate everything in their path."

Given the threat of swift destruction, Fink and Ramsey welcome the prospect of fast data and fast analysis.

"Making a quick-and-dirty, black-and-white image doesn't take very long--on a couple of minutes," Ramsey said. "For somebody who is right out there on the front lines with an erupting volcano, to get something like that could be very useful."