# Volcano Watch — Mauna Loa comes under military-style surveillance

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The internal workings of Mauna Loa Volcano will be probed from space starting this week by a satellite system designed to track military vehicles rather than volcanoes.

The internal workings of Mauna Loa Volcano will be probed from space starting this week by a satellite system designed to track military vehicles rather than volcanoes. Scientists from both the Hawaiian Volcano Observatory and the Cascade Volcano Observatory of the U.S. Geological Survey are deploying instruments on Mauna Loa that receive signals from a group of satellites that are the heart of the Global Positioning System, or GPS.

The high-tech positioning system was developed by the Department of Defense to provide accurate worldwide navigation. When fully operational in 1993, GPS will allow military users to quickly determine their location anywhere on the globe to within a few feet, 24 hours a day, in virtually any weather conditions. The system played a key role in Operation Desert Storm last year by helping to coordinate troop movements in the relatively featureless desert terrain of Kuwait and Iraq. A modified version is available for civilian use and is attracting attention from a variety of users, including scientists who keep track of active volcanoes.

By recording a large amount of satellite information at several points on the Earth's surface, and processing that information in a special way, we can increase the accuracy of GPS tremendously. The data collection points can be separated by many miles and by thick vegetation or steep terrain, because it isn't necessary to make line-of-sight measurements from one point to the others, as is the case for conventional surveys. To use the GPS, we only need a relatively clear view of the sky, so we receive the signals from the satellites. By returning to the same points at a later date with GPS, we can detect ground movements of less than an inch that may have occurred in response to magma moving underground.

Civilian uses of GPS such as that described here, have the military's blessing, because these accurate results require months of computer processing, and such after-the-fact information poses no threat to national security. Nonetheless, it is a new and exciting tool for scientists who study active volcanoes.

When magma moves deep within a volcano, it pushes aside the surrounding rock, causing the surface to move slightly. As an eruption nears, these movements often accelerate and become very large. As a result of the 1984 eruption of Mauna Loa Volcano, the summit subsided at least two feet, and the flanks of the volcano moved apart by nearly three feet. We interpreted these changes to indicate that at least 130 million cubic yards of magma withdrew from beneath the summit and erupted from the northeast rift zone.

The GPS survey at Mauna Loa has some urgency because our conventional measurements of deformationindicate that Mauna Loa has been inflating with magma since the end of the 1984 eruption. Those measurements have shown that the rate of magma accumulation has accelerated in the past six months and that Mauna Loa has now regained nearly two-thirds of the volume of lava erupted in 1984. The urgency to perform the GPS measurements reflects our desire to establish a multi-year base of data prior to the next eruption. GPS will allow us to make measurements that aren't practical with any other technique because of the long distances involved and the limited line-of-sight on Mauna Loa.

Mauna Loa was recently designated a "decade volcano" as part of the International Decade of Natural Hazards Reduction. This GPS survey is part of what we hope will evolve into an intensive, multidisciplinary study of the volcano during the coming decade, which will probably include the next eruption. We will also be deploying at least three new seismic stations and an electronic station to measure ground tilt along Mauna Loa's southwest rift zone within the next year. The GPS survey and the installation of new instruments are being done to improve our ability to forecast the next eruption and to monitor that eruption when it occurs.

### Volcano Activity Update

The eruption on the East Rift Zone of Kīlauea Volcano continues with very low-volume effusion of lava at about the 1,900-foot level of the tube downslope from the Kupaianaha vent. This is the same area that has had active flows for the past six weeks. The volume of lava continues to slowly decline, as it has since last summer. The active lava pond in Puu O`o continues to produce bright glow at night. All the earthquakes recorded this week had magnitudes less than 3.0.