Los Alamos National Laboratory
James E. Rickman, (505) 665-9203 / [email protected]
LOS ALAMOS RESEARCHERS SAMPLE MEXICAN VOLCANO FROM AFAR
LOS ALAMOS, N.M., July 14, 1997 -- Researchers at Los Alamos National Laboratory, in collaboration with scientists from La Universidad Nacional AutÛnoma de MÈxico are perfecting methods for sampling volcanic discharges from safe distances.
The methods, recently tested on Mexico's Popocatepetl -- an active, 17,800-foot volcano located about 50 miles southeast of Mexico City, home to 20 million people -- ultimately may help scientists and civil protection agencies forecast volcanic eruptions by alerting them to changes in the chemical composition of volcanic discharges.
Los Alamos researchers Fraser Goff, Steve Love and Dale Counce and UNAM vulcanologist Claus Siebe performed remote-sensing experiments on Popocatepetl earlier this year as the mountain continued to show signs of awakening by belching plumes of dark smoke high into the air. This effort was conducted within the framework of existing volcano-monitoring activities coordinated by Centro Nacional de Prevencion de Desastres, the Mexican institution for disaster mitigation.
But even when the smoke wasn't there, the trio's remote-sensing gear was able to "see" what was coming out of the volcano -- which hasn't had a major eruption since about 800 A.D., when the mountain laid waste to the surrounding area.
"When a volcano isn't putting out smoke, ash and lava like it might do during a full-scale eruption, it still can release tons of chemical compounds into the atmosphere through its vents each day," said Goff, a vulcanologist in Los Alamos' Geology and Geochemistry Group. "These gases can affect climate and create possible health risks so it's important to be able to accurately monitor the abundance of these chemicals. But what might be even more important is being able to see how the abundance of certain constituents changes just before an eruption. These changes can be possible harbingers of eruptions. If we can identify these changes, eventually we may be able to predict eruptions."
To test whether their instruments could see invisible plumes coming out of the volcano, the research team set up shop at several locations two to six miles from the simmering summit.
Love, who works in Los Alamos' Astrophysics and Radiation Monitoring Group, used an instrument called a "Fourier transform infrared spectrometer" to gain measurements of some of the more elusive invisible constituents.
"On the trip to Popo we were really trying to get an idea of what we could do to improve the sensitivity of our detections," Love said. "I learned a trick for using sunlight reflected off of clouds to gain the sensitivity we needed to detect hydrofluoric acid and hydrochloric acid in plume gases. No other vulcanology group has been able to measure HF in the field."
Hydrofluoric acid and hydrochloric acid 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 acids.
Love realized that he could get more sunlight into his instruments and detect the acids more easily if he took advantage of sunlight scattered off of clouds. Field tests proved Love's assertion and the team was able to detect the acids in the plume from as far as four kilometers away.
Infrared spectroscopy helped the researchers measure amounts and temperatures of plume constituents.
The typical volcano releases through its vents about 90 percent water, six percent carbon dioxide and two percent sulfur dioxide; all other constituents, including hydrofluoric acid and hydrochloric acid, make up the remaining two percent, Goff said.
Counce, a researcher in Los Alamos' Geology and Geochemistry Group, used an instrument called a "correlation spectrometer" to determine gross levels of sulfur coming out of the volcano. The "cospec," as it is known, effectively measures the amount of sulfur dioxide discharged into in the atmosphere by the volcano.
The data are useful for interpreting the infrared results because the cospec provides absolute sulfur dioxide readings that don't depend on temperature, whereas the size of the infrared sulfur dioxide signal depends on the temperature of the plume. Combining the two measurements allows scientists to calculate the temperature of the plume. The concentrations and temperatures of sulfur dioxide are important in analyzing the infrared spectra.
"Since carbon dioxide and water vapor are prevalent in the atmosphere, it's a pretty complicated calculation to get the atmospheric CO2 and water out of the picture," Love said. "It's fairly easy to get the relative amounts of plume constituents from the infrared spectra, but difficult to get an absolute concentration of any one particular constituent. With the absolute sulfur dioxide concentration from the cospec, we can calibrate the concentrations of all the other gases."
During the trip to Popocatepetl last spring, Counce was able to measure some 60,000 tons of sulfur dioxide coming out of the mountain during one exciting day, she said. The mountain typically discharged five thousand to 15,000 tons of sulfur dioxide a day.
"Popo has become one of the largest natural emitters of sulfur dioxide in the world, rivaling Mount Etna in Sicily" Goff said.
Goff, a seasoned vulcanologist who has taken samples from the vents of many active and deadly volcanoes, chose Popocatepetl for the remote-sensing experiments because of the sheer abundance of constituents the mountain spews into the air, and because collaborative investigations on geoscientific topics already have been established with Mexican scientists and authorities. The large production rates allow the team to fine-tune their remote-sensing procedure.
Counce, who had her first experience with volcanoes during the Popocatepetl excursion, said it was slightly unsettling when the mountain sent plumes of ash skyward.
The remote-sensing techniques eventually could be used by satellites and airplanes to gather volcano data while putting researchers well out of harm's reach.
In addition, Goff said, by correlating the remote-sensing data with seismic data, vulcanologists should be able to develop methods for accurately predicting eruptions.
For areas like Mexico City, with its 20 million inhabitants, early warning could be crucial for successful evacuation and emergency preparedness.
Los Alamos researchers also gathered remote-sensing data in New Zealand and have been working with officials from the Public Service Company of New Mexico to take remote-sensing data from the San Juan Generating Station -- the "Four Corners Power Plant." Emissions from the plant simulate some volcanic emissions and provide an opportunity for the researchers to calibrate their instruments with known emissions quantities.
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.
Since the vulcanology team made their visit in February, Goff said, Popocatepetl has been relatively quiet except for two or three unpredictable, but short explosions. The latest one on June 30 blew an ash cloud approximately 10 kilometers above the summit. The cloud spread over Mexico City during the afternoon, where rush-hour commuters were greeted by wet ash on their windshields. Residents complained about the acrid smell of sulfur gases. The blast temporarily closed Mexico City international airport. Since then, the volcano has calmed down, at least for now, he said.
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy.
-30- Note to editors: A photo of the researchers working at Popocatepetl is available.
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