M S Ramsey and J H Fink (Both at: Department of Geology, Arizona State University, Box 871404, Tempe, AZ, 85287-1404 USA; 602-965-5507; email: firstname.lastname@example.org)
In June 1998 NASA will launch the first Earth Observing satellite designed to characterize long-term environmental changes and monitor potential natural hazards. The Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) will be part of that payload and will provide the first world-wide multispectral data from the visible to the thermal infrared (TIR). Among the prime geologic targets for ASTER will be the hundreds of volcanoes around the world. Monitoring of active flows and domes using thermal infrared data will not only provide information on lava temperature, but also mineralogy and vesicularity. The surface vesicle content of large basaltic flows is of interest since it may be related to emplacement time, volatile content, paleoelevation, and internal structure. In addition, studies of flow inflation have also made understanding vesicle distribution important.
Vesicularity produces variations in thermal emission data that are easily distinguishable. For example, a pahoehoe lava flow can be described as a surface consisting of two spectral endmembers, basaltic glass and bubbles. The distinct spectral feature of glass is commonly muted due to the overprinting of the vesicles, which can be modeled as featureless blackbody radiators. With the assumption that the blackbody energy combines linearly in direct proportion to the areal percentage of vesicles, the TIR data can be deconvolved to estimate the abundance of bubbles. This new technique using a linear retrieval model to produce vesicular maps has been extensively tested on recently emplaced silicic domes with great success.
The purpose of this study was to apply the same technique to airborne TIR data collected over well characterized, recent flows at Kilauea. Field mapping and model verification show that the technique works extremely well predicting vesicle percentages for the uppermost chilled surface. In areas where this rind was removed by mechanical weathering or flow over steep slopes, the modeled bubble content more closely resembled the average surface vesicularity of pahoehoe (~ 60%). Textural variations (pahoehoe versus aa) were also able to be mapped.
Future monitoring of active volcanism using remote sensing will require developing this sort of analytical technique in addition to better characterization of the physics of thermal emission from glassy surfaces.
Presented at: American Geophysical Union Fall Meeting