Appearances count in volcano monitoring

When asked to recite the most important volcano monitoring methods, volcanologists will invariably include seismic monitoring, deformation monitoring, and gas monitoring. Visual monitoring — systematic observations of a volcano’s outward appearance — is usually not mentioned. Yet the outward appearance and changes in the outward appearance of a volcano provide information as important as that provided by the other monitoring methods. Visual monitoring is a fundamental monitoring tool.

The eye — the sense organ upon which we rely most heavily — was almost certainly the first volcano monitoring tool. Long before science was a career option, our distant ancestors learned — probably the hard way — that it was a good idea to keep an eye on the neighborhood volcano. When volcanology first became a distinct science, it was mostly descriptive and was based on careful visual observations of volcanoes.

Today, scientific instruments replace or augment our senses as monitoring tools because instruments are faster and more sensitive, work tirelessly day and night, keep better records, operate without complaint in hazardous areas, do not generate lawsuits when damaged or destroyed, and, in most cases, are cheaper than volcanologists. Furthermore, instruments are capable of detecting phenomena that are outside the reach of our senses.

Nonetheless, there is still no substitute for the eyes of an experienced volcanologist. But those eyes are now augmented by cameras that deliver sequences of timed photographs to volcano observatories. Volcanologists review the recorded sequences as fast-forward animations to quickly identify changes in volcanic behavior, to understand volcanic phenomena, to monitor the rates at which ongoing processes are occurring, and even to detect eruptions. Often, the photographic record provides a basis for interpreting puzzling data collected from other monitoring methods.

Incandescence and glow are, of course, visible to the naked eye and to cameras at night — in fact, both are usually much more obvious at night than during daylight hours. But standard cameras, like eyes, don’t work as well when the volcano is obscured by bad weather or volcanic fume. This is because visible light is scattered by the tiny liquid droplets that form clouds and volcanic fume. The summits of some volcanoes are nearly always hidden in clouds.

The “hidden volcano” problem can be overcome by using instruments that employ radiation that isn’t scattered by tiny liquid droplets and can thus see through clouds. Radiation with a wavelength between about 1 millimeter to 30 centimeters (about 0.04 to 12 inches) can do the job. Such instruments exist, but they are more expensive and less convenient to use than conventional cameras, so their use in volcano monitoring is still rather limited. However, we can expect all-weather imaging systems to become more widely used on volcanoes as the technology matures and the costs decrease.

Current panoramas from cameras on the north rim of Kilauea’s Pu`u `O`o crater and on the northwest rim of Moku`aweoweo caldera on Mauna Loa may be viewed on the Internet at the Hawaiian Volcano Observatory website (

Activity Update

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater. Lava continues to flow through the PKK lava tube from its source on the flank of Pu`u `O`o to the ocean. In the last week, the only surface flow activity was along the margins of the “Campout flow,” which reached the ocean at East Ka`ili`ili on the night of August 3. As of August 10, the new ocean entry, which is located 7.8 km (4.7 mi) from the end of Chain of Craters Road, was still active.

Lava is still entering the ocean at East Lae`apuki, also in Hawai`i Volcanoes National Park. The lava bench is rapidly refilling the gap left by the partial collapse on July 30, and, as of August 4, had a total surface area of about 20 ha (50 acres).

Access to the sea cliff near the ocean entries is closed, due to significant hazards. The National Park has reopened the surrounding area, however. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

Two earthquakes beneath Hawai`i Island were reported felt during the week ending August 9. Both were located 5 km (3 mi) south of Volcano. The first, which occurred at 1:47 p.m. on August 3, had a magnitude of 1.5 and a depth of 3 km (1.8 mi). The second, at 3:19 p.m. on August 6, had a magnitude of 3.2 and a depth of 4 km (2.4 mi).

Mauna Loa is not erupting. During the past week, one short-period earthquake was recorded beneath the volcano’s summit. Extension of distances between locations spanning the summit, indicating inflation, continues at slow rates.

This article was written by scientists at the U.S. Geological Survey’s Hawaii Volcano Observatory and is republished by with permission.

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