October 25, 1996

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Monitoring Volcano Movements with Satellites

The shape of active volcanoes is constantly changing. Large movements occur during dike intrusions, large earthquakes, or landslides. Smaller movements occur as magma moves through the volcano's plumbing system or in response to gravity and other forces that slowly deform the volcanic pile. The small movements can be detected only with very sensitive instruments. For example, in order to track the slow filling or emptying of a summit magma chamber buried at a depth of several miles, we need surface measurements that are accurate to a fraction of an inch. Monitoring these movements is important because they provide us with clues about what is happening inside the volcano and where and when the volcano may erupt.

In the last decade, new satellite technologies, such as the Global Positioning System (GPS), have revolutionized our ability to monitor ground movements. Volcanologists use special GPS receivers and sophisticated computer programs to measure ground movements to an accuracy of a fraction of an inch. Until recently, most of these measurements were made only once or twice a year. These annual surveys provided average movements but did not allow us to track sudden changes, such as those caused by intrusions of magma or eruption pauses. More frequent measurements were needed to catch fast-acting volcanic events.

To improve our ability to monitor volcanic events on Kilauea Volcano, Stanford University and the Hawaiian Volcano Observatory began installing a network of seven continuously recording GPS receivers during the summer of 1995. The University of Hawaii at Manoa joined this effort in the summer of 1996 and installed six more receivers on Kilauea's south flank. Our current 13-station GPS network provides accurate and timely ground displacements. We use this information to determine long-term deformation trends and to detect changes that may forecast eruptions, earthquakes, or landslides.

The continuous GPS network supplements our other frequent deformation monitor, a network of electronic tiltmeters. In contrast to GPS, which provides data on three-dimensional ground displacements, tiltmeters provide data only on slope changes. Our tiltmeters are installed near the summit and rift zones of the volcanoes and can detect nearby intrusive events. Tiltmeter data, however, are plagued by high background noise and electronic drift, making detection of subtle changes problematic. Continuous GPS data provide a more complete and accurate measure of the ground deformation.

Although space-age technologies, such as GPS, have already improved our ability to monitor active volcanoes, further improvements are in the works. An experimental technique called interferometric synthetic-aperture radar (I-SAR) will someday allow us to produce detailed maps of ground deformation without putting out any instruments. I-SAR uses satellite recorded radar images of the Earth's surface to generate, among other things, topographic maps. Images recorded at different times by the same satellite can be "differenced" to produce an interferogram, or picture of ground deformation. Our efforts to mitigate volcanic hazards are improved by these space-age technologies, which provide timely, detailed, and accurate tracking of volcanic events.

Eruption Status

The current eruptive activity of Kilauea Volcano continues unabated with lava flowing from the Pu'u 'O'o vents through a network of tubes down to the ocean near Lae'apuki.

Residents of Hawaiian Acres, Mt. View, Glenwood and Volcano were shaken by a magnitude 3.2 temblor on October 21 at 5:13 p.m. The earthquake was located 5 miles southwest of the summit of Kilauea Volcano at a depth of 16 miles.