"Basically, after spending four years of taking infrared measurements of volcanic gases at volcanoes around the world, we've been fortunate enough to record a number of scientific surprises, as well as some pitfalls associated with our remote sensing techniques," said Love. "In order to get accurate measurements and trends, you need to take frequent measurements over an appropriately long period of time."
Using both infrared and ultraviolet spectrometers - instruments that allow researchers to see the spectral "fingerprints" of gaseous chemicals being discharged by volcanoes - Love and Los Alamos volcanologist Fraser Goff studied volcanoes at all points of the compass to learn whether the composition or volumes of volcanic gases change when an eruption is imminent.
Love and Goff so far have found one spectroscopic clue that may precede an eruption. At Mexico's Popocatépetl - an active, 17,800-foot volcano located about 50 miles southeast of Mexico City, home to 20 million people - the researchers found that the amount of silicon tetrafluoride gas being released increased noticeably relative to the amount of sulfur dioxide gas prior to eruption. The amount of silicon tetrafluoride dramatically increased just after the eruption and then quickly returned to pre-eruption levels hours later.
This detection gives the researchers hope that volcanoes really can put out a chemical semaphore that signals impending eruption.
Interpreting remote sensing data takes care, however, Love said.
For example, during their second trip to Popocatépetl, Love was stunned to discover that every now and then the volcano would blast out a huge cloud of carbon dioxide, which they had not seen previously. Continued spectroscopic monitoring of the mountain showed that Popocatépetl regularly spewed CO2 blasts, which were typically a hundred times larger than what they'd see coming from the mountain at other times.
The increase in CO2 probably was the result of limestone, which lies as a foundation below Popocatépetl, being incorporated into magma and releasing the gas in the process. The observation helped the researchers realize that, unless measurements were made very frequently - at intervals of a few minutes or so - they could significantly underestimate the average amount of CO2 being discharged annually by the volcano.
The lesson from Popocatépetl was that remote sensing measurements must be sufficiently frequent and conducted over a long enough period of time to ensure accurate measurements.
Love learned other tricks, too. At Colima volcano in Mexico and at Mt. Etna in Italy, Love found that he could use incandescent light from lava in the volcano to help detect hydrogen fluoride and hydrogen chloride gas. The gases are difficult to detect using infrared spectroscopy because their spectral fingerprints lie at wavelengths at which there is very little natural light. Under a clear sky, the infrared spectrometer has to rely solely on very dim thermal radiation to see the gases. Love learned that a pool of glowing lava in a caldera, or red-hot rocks being ejected into the sky could be used to provide enough illumination for him to get a look at the two gases and measure their concentrations.
But remote sensing of hydrogen fluoride and hydrogen chloride gas presents its own set of pitfalls. Because volcanoes discharge small particles of ash, cinder and other materials into the air, they effectively provide material onto which water vapor can condense - in essence, they act as "cloud seeders." When clouds form over volcanoes, the water vapor in the cloud effectively scrubs the atmosphere of hydrogen fluoride and hydrogen chloride, which are extremely soluble in water. Infrared remote sensing can only detect hydrogen fluoride and hydrogen chloride in their gaseous form; these chemicals become invisible when dissolved in water. Consequently, Love learned that spectroscopic measurements of those two gases must be taken before the clouds form.
Los Alamos has a strong interest in remote sensing of chemical plumes because such sensing has wide applications to programs in global climate and atmospheric change, and environmental pollution monitoring. Automated remote sensing stations someday also could provide an early warning system for people who live near volcanoes, whose eruptions have killed tens of thousands of people and caused millions of dollars of property damage in just the last three decades alone.
"Remote sensing of volcanoes as an early-warning method shows a lot of promise, but you have to be aware of its limitations." Love said. Los Alamos National Laboratory is operated by the University of California for the National Nuclear Security Administration (NNSA) of the U.S. Department of Energy and works in partnership with NNSA's Sandia and Lawrence Livermore national laboratories to support NNSA in its mission. Los Alamos enhances global security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health and national security concerns.
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