HR: 0800h
AN: V31B-0483    [Abstracts]
TI: Physical Properties of Volcanic Material (Tephra) Using Visible Near-Infrared Spectroscopy
AU: * Necsoiu, M
EM: mnecsoiu@swri.org
AF: Department of Earth, Material, and Planetary Sciences (DEMPS), Southwest Research Institute®, San Antonio, TX 78238, United States
AU: Hooper, D
EM: dhooper@swri.org
AF: Center for Nuclear Waste Regulatory Analyses (CNWRA), Southwest Research Institute®, San Antonio, TX 78238, United States
AU: Roseberry, J
EM: jroseberry@swri.org
AF: Department of Earth, Material, and Planetary Sciences (DEMPS), Southwest Research Institute®, San Antonio, TX 78238, United States
AB: Sunset Crater, Arizona, offers the opportunity to investigate the relationship between visible near-infrared reflectance and physical properties of volcanic material as related to the evolution of a 900-year-old tephra deposit in a semiarid climate. This is an analog area for latent eruption and posteruption surface processes near the potential high-level waste repository at Yucca Mountain, Nevada. Quantitative and qualitative analyses were performed on tephra modified by eolian processes to investigate the effects of grain size, shape, texture, and weathering on spectral response. Reflectance spectra were collected from homogeneous sample splits separated by sieve fraction. Principal component analysis (PCA) was applied to decompose data by finding maximum variances, so the complexity of tephra samples could be easily interpreted. Partial least squares (PLS) was used for developing a linear calibration model between grain size and spectral reflectance of sieve fractions. The model was used to estimate grain-size distributions of other tephra samples collected from other locations in the study area. The trends observed in the spectral reflectance of these samples showed that a complex relationship exists between reflectance and geometry/grain size of the analyzed fractions. The first and second principal components were useful to separate the samples based on shape, texture, and the amount of weathering. As expected, the grain size of a homogeneous sample affects the reflectance properties such that an increase in grain size produces a decrease in reflectance. This trend is noticeable for grain-size sieve fractions less than 0.6 mm [0.02 in]. Through this research, we are improving our understanding of the relationships between physical properties and spectral response of volcanic material in the visible and near-infrared regions. These relationships are being used to support investigations of the extent of tephra deposit remobilization and redistribution, resuspension, rates of weathering and erosion, and grain-size characteristics. This abstract is an independent product of the CNWRA and does not necessarily reflect the view or regulatory position of the U.S. Nuclear Regulatory Commission.
DE: 3625 Petrography, microstructures, and textures
DE: 8404 Volcanoclastic deposits
DE: 8494 Instruments and techniques
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting