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Volcanowatch

August 26, 2010

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


Pushing the monitoring envelope

Interferogram of Kīlauea, showing topographic fringes (NASA/JPL-Caltech).
Interferogram of Kīlauea, showing topographic fringes (NASA/JPL-Caltech).

Like other volcano observatories, HVO devotes most of its resources to volcano monitoring, using time-tested methods that have been found to deliver data useful for understanding and forecasting volcanic behavior. But the monitoring toolkit is not static; it evolves as new technologies become available and as new monitoring strategies are introduced.

Before a new method is adopted, someone has to imagine it—and imagine that it might be superior to an existing method or provide information that is otherwise unavailable. Many volcano-monitoring tools have been adopted from other disciplines, when a volcanologist recognizes the applicability to volcanology. Two examples are interferometric synthetic aperture radar (INSAR) and Doppler radar. INSAR can detect subtle changes in the earth's surface over broad areas. Doppler radar—used to detect and track plumes from explosive eruptions—was adopted from the meteorological community. Doppler radar images are frequently seen on television weather forecasts. Both INSAR and Doppler radar evolved from radar developed for military applications.

The idea for a new method may spring from a chance observation. For example, pioneering volcanologist Frank Perret, responding to a volcanic crisis at Vesuvius in 1906, wrote: "At the Eremo Hotel, opposite the Royal Observatory, I thought I could hear in the dead of night a low buzzing sound. On opening the window the buzzing ceased, but with my ear to the pillow it again became distinctly audible. With my teeth in contact to the iron bedstead the noise was unquestionably louder, and there was no doubt in my mind that a contact microphone would have shown the sound to be of subterranean origin, definitely premonitory of threatening danger."

Whatever the source of the idea, it needs to be tested. The outcome of such a test is of course uncertain—otherwise the test wouldn't be necessary. Many "good ideas" don't pan out. Frank Perret constructed and tested his contact microphone, but it has not become part of the modern toolkit. On the other hand, seismographs, which measure lower vibrational frequencies, have become the foundation of the volcano-monitoring toolkit.

Observatories can devote only a small fraction of their resources to testing new ideas—just as a prudent stock portfolio manager will allocate only a small fraction of a portfolio to high-risk but potentially high-return stocks.

HVO currently has several speculative stocks in its portfolio. One is the use of multiple continuously recording gravimeters—instruments that accurately measure the pull of gravity. Gravity measurements can detect subtle density changes caused by magma movement beneath the instrument. Gravimeters are notoriously difficult to operate and, traditionally, each measurement has been made manually. The use of continuously recording instruments is new-and experimental.

The study of lava-tube tremor is also experimental. This study was designed to test the idea that fluid motions in flowing tube-lava would generate vibrations. It was hoped that the amplitude and/or frequency of the vibrations would track the lava flux—that is, the rate at which lava flows through the tube. If this were true, we could monitor the changes in K?lauea's output in real time. Data collected from seismometers placed atop lava tubes show that lava tubes do indeed produce continuous vibrations, or tremor. And it appears that the tremor amplitude tracks the lava flux over periods of at least a week. Future experiments will collect data over longer time periods.

A third experiment will deploy a number of thermal infrared web cameras. Infrared light penetrates ash and fume better than visible light, so these cameras should be able to provide continuous images of the lava lake within Halema`uma`u Crater. The visible-light cameras currently in use can only see through the fume at night. In addition to images, these new cameras also provide quantitative temperatures that can be monitored for unusual changes over time.

All of these experiments—and others not described—are promising. But they will find their way into regular use only after testing demonstrates that the information they provide is sufficiently useful to justify the cost of procurement and maintenance in a challenging environment.

Kīlauea Activity Update

There were several small breakouts just west of the end of Highway 130 last weekend, and a few small breakouts on the Puhi-o-Kalaikini delta at mid-week. All were short-lived and posed no threat to the nearby Kalapana Gardens subdivision. A series of inflation-deflation cycles, ongoing at Kīlauea's summit for the past several weeks, may result in fluctuations in the size of the ocean entry plume over the coming days and could result in more small breakouts on the coastal flow field.

At Kīlauea's summit, a circulating lava pond deep in the collapse pit within the floor of Halema`uma`u Crater was visible via the Webcam throughout the past week. The lava surface rose and fell slowly to match the series of deflation-inflation cycles. This slow change in lava level was punctuated on several occasions by abrupt increases in the height of the lava surface. These periods of high lava level were short-lived, lasting up to several hours, and ended with a sudden drop of the lava surface back to its previous level. Volcanic gas emissions remain elevated, resulting in high concentrations of sulfur dioxide downwind.

Three earthquakes beneath Hawai`i Island were reported felt during the past week. A magnitude-2.5 earthquake occurred at 3:31 p.m. on Thursday, August 19, 2010, H.s.t., and was located 6 km (4 miles) west of Kīlauea summit at a depth of 9 km (6 miles). A magnitude-3.1 earthquake occurred at 3:01 p.m. on Monday, August 23, and was located 15 km (10 miles) west of Pahala at a depth of 8 km (5 miles). A magnitude-2.7 earthquake occurred at 3:26 p.m. on Wednesday, August 25, and was located 16 km (10 miles) west of Kīlauea summit at a depth of 11 km (7 miles).

Visit our Web site (http://hvo.wr.usgs.gov) for detailed Kīlauea and Mauna Loa activity updates, recent volcano photos, recent earthquakes, and more; call (808) 967-8862 for a Kīlauea activity summary; email questions to askHVO@usgs.gov.

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Updated: September 7, 2010 (pnf)