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Photonics Contributes to Lava Flow Study

Photonics Spectra
Jul 1998
Ruth A. Mendonsa

Among the many attractions of the Hawaiian Islands, perhaps the most intriguing are its volcanoes. Tourists are drawn by their beauty and by the danger that lies within. But these mountains, formed by the accumulation of molten rock, can become a threat to lives and homes without warning.

Lava flow temperatures averaging 1150 °C were detected using the FieldSpec FR at this erupting volcano. Courtesy of P. Mouginis-Mark.

Luke Flynn at the University of Hawaii's Institute of Geophysics and Planetology is employing a spectroradiometer to monitor volcanic activity on the islands. He is using the FieldSpec FR from Analytical Spectral Devices (ASD) to capture lava flow spectral data that can be translated into actual flow temperatures. He compares the satellite data of the Hawaiian Islands to the hyperspectral data from the spectroradiometer to determine the temperatures of the active lava flows, which are directly related to how old the active flows are.

The different temperatures of the lava flows tell the story of their activity. According to Flynn, the most important temperature is that of the magma when it stops flowing, which is generally 770 °C. Any areas with temperatures above that measurement would signal active lava flows. Although all lava flows are different, a cross section of a typical flow reveals the edges to be the hottest, at 750 to 1150 °C, and the crusted-over areas in between at 400 to 500 °C.

The device's rapid data collection, light weight and compactness are key to its success in this endeavor. In some cases the temperature of the target is an average of 1150 °C and is moving at 10 to 15 mph, so the FieldSpec also is used to measure lava flow temperatures from a helicopter.

Flynn said he chose the FieldSpec FR for all these reasons, but the most important is the speed at which measurements can be taken. Because there is significant cooling in the first 20 minutes after an eruption, every second counts. The instrument he used previously took a minute or two to complete a spectrum from 10 scans, which is unacceptable because the temperature can change by 100 °C in that time. The FieldSpec FR, on the other hand, completed the spectrum in 1 to 2 seconds. The instrument also can be set up to take any number of spectra at any given time interval, which frees the user to take care of other tasks, such as operating a video camera or checking out other flows.

"It's a one-person operation," said Flynn. "The ASD [instrument] is the first instrument I've had that if some big event happens -- some lava flow busts out from somewhere -- you can literally walk over and begin gathering data."

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