Some of the changes in volcano-monitoring technology and equipment that have occurred since the 1980 eruption of Mount St. Helens:

Seismic monitoring: Seismometers in 1980 had only one main component and their signals were recorded on paper graphs. Now, seismometers are more sophisticated and include other sensors and microphones. The complex data can be sent at much higher speeds to be stored and analyzed instantly by computers.

Volcano deformation: Changes in the actual shape of the volcano had to be measured with heavy mapping cameras using film, aerial photos or electronic distance meters that used triangulation techniques for more precision. It sometimes took days of intensive labor to record the measurements. Today, Global Positioning System units instantaneously show changes in the shape of the volcano, along with laser radar imaging.

Gas analysis: Airborne sulfur dioxide was measured in 1980, and some volcano vents could be sampled for other gases. Now, airborne-gas analysis extends to carbon dioxide and hydrogen sulfide, offering important additional clues to volcano behavior. Sampling and analysis equipment have greatly improved the speed and reliability of analysis, and scientists are testing remote-control drones to fly close to the volcano when it is too dangerous for pilots.

Field observations and rock analysis: Field observations have not changed much, but the communications technology has greatly improved, along with the addition of digital cameras and laptop or palm computers. Rock and mineral analysis has gotten faster, and new methods such as plasma and infrared spectrometers have been developed that can detect trace elements at extremely low levels.

Hydrology: In 1980, the streams flowing off the mountainside had to be visited in the field to determine or map changes. Today, acoustic-flow monitors transmit data for analysis, and new computer models can predict flow paths of lahars.

The Associated Press