Blowing the lid off mighty volcanoes

Moments after the 8:32am eruption, he was killed by a gigantic blast of rock, heat and gas. His body was never found.

But new equipment developed in the 24 years since the last eruption has made it possible for volcanologists to take better measurements without having to hike up the volatile mountain - a requirement that cost Johnston his life.

Much of this equipment has been used this week, after several days of steam and ash eruptions. "Those measurements can be made remotely now with GPS equipment. You don’t need to be up there on the volcano," says Dan Dzurisin, who was Johnston’s friend and colleague.

Instruments that encircle the mountain prompted scientists to announce on Wednesday that the danger of a sudden strong eruption had passed.

Deformation - changes in the shape of a volcano - can now be measured in three dimensions. Laser reflection systems in use in 1980 could only detect changes in one direction. The more sophisticated Global Positioning System (GPS) instruments would have revealed movement in the mountain that was not detected by the final reading Johnston made before Mount St Helens exploded. "Today, we would have known," says Dzurisin.

Other tools have been added to the volcano kit for geologists over the past quarter-century and computers have greatly enhanced analysis of the data received from those sensors. "Gee, let me count the ways it’s gotten better," says Jake Lowenstern, part of the team working at Mount St. Helens. As well as GPS sensors that can detect movement of just half an inch, scientists can use infra-red heat detectors and specialised radar to track changes in a volcano, he added. Seismometers - which detect earthquakes - are also more sophisticated, reliable and numerous. Tremors are usually precursors to an eruption.

NEWER SEISMOMETERS separate volcano movement into 3D data, says Lowenstern: "In 1980, there was only one component - you were just watching up-and-down movement."

Deformation and seismic activity, as measured by this improved equipment, are two of the three key indicators that scientists rely on to make predictions about volcanoes. Advances also have come in measuring the third: volcanic gas emissions. Now scientists can fly over a volcano and take gas samples, using GPS systems to track the flight so that computers can give details on changes in levels and concentration.

Also, scientists can use microphones to measure noise from shifting rock, and video cameras to constantly monitor areas that otherwise could be inspected only periodically.

The most important change, however, is the improvement in telemetry: transmission of data from remote-control instruments by radio, microwave or even mobile phone.

"There was essentially no way in 1980 to do anything remotely," says Lowenstern.