Hazard Mitigation Associated with Silicic Dome Emplacement: Monitoring Surface Textural Variations Using Remote Sensing
1
1 Department of Geology and Planetary Science, University of
Pittsburgh, Pittsburgh, PA, 15260, USA.
2 Department of Geology,
Arizona State University, Tempe, AZ, 85287, USA.
Silicic domes and flows commonly show convoluted textural and compositional mixing patterns. On actively forming lava surfaces, texture variations can indicate a change in the extrusion rate, cooling, and/or degassing state of the magma. Because domes frequently form the late stage products of an eruption sequence, their presence can either signal the cessation of explosive activity or the beginning of a period of growth and collapse, leading to pyroclastic flows. Monitoring these surface changes is commonly difficult due to the dangers of continued explosive activity. However, under the appropriate conditions, the use of multispectral thermal infrared (TIR) remote sensing provides a measure of safety for field investigators and is uniquely sensitive to compositional, textural, and thermal changes. TIR data have rarely been used in the past to investigate active domes because of the lack of repetitive, high resolution, multispectral data.
The Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) instrument was launched in December of 1999 aboard the NASA Terra satellite. ASTER is now providing the first high-resolution (15-90 m), multispectral imagery spanning from the visible to the TIR wavelengths, with a telescope configuration that allows for along-track DEM generation. Thermal anomaly detection at active volcanoes is an ASTER priority. However, correct temperature retrievals will depend greatly on the accuracy of the DEMs and the effects of surface texture. Further, textural mapping may ultimately prove an important hazard monitoring tool in its own right.
TIR emissivity spectra of lavas can be modeled to produce an estimate of the vesicularity using a technique developed by the authors. Because the emitted energy is scattered by roughness at the wavelength scale (~ 10 µm), a model designed to separate the effects of this scattering will also produce a measure of that roughness. We employee a modified linear deconvolution approach to estimate the percentage and distribution of vesicularity. Field measurements were collected on the areal extent, vesicularity, and vertical roughness of silicic lava textures on rhyolite and dacite domes in the southern Cascades of the United States. Over the next three years this study will be expanded to recently active volcanoes using ASTER.
Results of this study are important because we have been able to quantify each sub-pixel element and refine our vesicularity model. Although detailed field studies will rarely be possible on active domes, this study lays the groundwork for calibration of future ASTER data and the development of a new monitoring tool.
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Submitted: IAVCEI General Assembly, Bali, Indonesia
Date: July, 2000