Active silicic volcanoes commonly produce hazardous domes and flows that are erupted either as gas-rich lavas with a range of bubble and glass contents, or as denser piles of rubble and blocks like the ongoing eruption of Mt. St. Helens volcano. The former style can alternate between dome extrusion and hazardous explosive eruptions. The latter style is commonly less hazardous, but if large enough can still collapse catastrophically forming deadly block and ash flows. To assess the hazards associated with active lava domes, many pieces of information are needed including the dome's type/composition/temperature. However, it is typically too risky to collect hand samples directly (as was the case at during the first few weeks of the Mt. St. Helens eruption in 2004). Remote techniques for monitoring active lava dome composition and temperature are more desirable and the data best-suited for these measurements are in the thermal infrared (TIR) wavelength region. TIR data can be collected from space or field instruments, which are located safely away (several kilometers) from the active vent. TIR wavelengths are sensitive to both the emitted heat as well as the mineral composition of these domes. In order to quantitatively understand the TIR signal from natural lava domes, critical laboratory-based data are needed however. The investigators are proposing to collect data of natural glassy and molten materials in the laboratory using a micro-scale furnace developed under a previous grant in order to extend this research to the field by adapting a thermal camera (FLIR) to capture multispectral data, which will simulate the data collected from space. The research proposed has important theoretical implications for TIR spectroscopy/remote sensing data analysis as well as practical applications for volcanic hazard monitoring/mitigation. The laboratory results will be compared to field and satellite TIR data and will provide information that will aid development of the next-generation of field-based monitoring tools. This project will support a fruitful international collaboration and fund both a Ph.D.-level graduate student as well as a several undergraduate students.
Specifically, it is proposed to do a follow-on research study comprised of laboratory and field-based tasks to characterize silicate TIR emission data produced by vibrations of the fundamental Si-(Al)-O units. In the first task, they will use their existing laboratory FTIR spectrometer and the recently-fabricated micro-furnace to provide the first systematic characterization of the diagnostic TIR absorption band positions/shapes of silicate glasses and melts. Specifically, they will focus on three states in the laboratory studies: (1) samples above the solidus and the glass transition temperatures, (2) the glassy crusts that initially form on lava and mineral melts upon cooling, and (3) the final interstitial matrix glass of mineral and natural silicic samples. They will collect the full TIR spectral range of the laboratory spectrometer (5-25 micrometer or 2000-400 cm-1), but concentrate on the region of the Earth''s atmospheric window (8-12 micrometer region or 1250-830 cm-1) in order to compare the data directly to those collected by satellite and from the field. The 8-12 micrometer region is also the location of the strong absorption bands (dominantly Si-O and also Al-O) in the silicate minerals and glasses. The proposed research will advance our understanding of infrared spectroscopy, molecular-scale glass and melt structure, and surface processes on both active and inactive lava domes. However, for TIR spectroscopy to be an accurate monitoring tool, the factors that affect the emitted TIR energy from active dome surfaces must be better-understood. Specifically, TIR emission is influenced by the formation of cooled/cooling glassy crusts, the structure and percentage of glassy matrix, other coatings such as sublimates, as well as the intervening atmosphere. The second task of this proposed research is field-based. It is planned to purchase wavelength filters for the P.I.'s TIR broadband camera that will convert it into a field-based spectrometer. The data collected from this modified instrument will allow an application of the laboratory results to field data of inactive silicic domes. This will be the first time such a camera will be used in this way and the hope is that it will lead to eventual construction of a rugged monitoring instrument capable of deployment on remote volcanoes and used for monitoring and derivation of fundamental physical properties of the lava dome (e.g., surface vesicularity, phenocryst composition and percentage, glass composition and percentage, and temperature) in real time.
