M. Ramsey, R. Wessels, and C. Eisinger (All at: Department of Geology, Arizona State University, Box 871404, Tempe, AZ 85287-1404; 480-965- 5507; email: ramsey@elwood.la.asu.edu)
For decades, remote sensing has been used to map and monitor volcanic systems with a wide variety of sensors, techniques and resultant products. Volcanic hazard mitigation will also form a key component of the upcoming NASA Earth Observing satellite, which will carry several instruments that employ high temporal, spectral and/or spatial resolutions ideally suited for eruption monitoring. Of these, the Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) instrument will be the only one to image the earth's surface at high resolution in the thermal infrared (TIR) region and generate optically- derived DEMs. Both these features will be critical in assessing the accurate location and percentage of vesicularity and thermal anomalies. However, TIR remote sensing is hindered during times of heavy cloud cover and is not sensitive to lava roughness/block size greater than the millimeter scale. The use of polarimetric and interferometric radar remote sensing does overcome both these shortfalls, but reveals little about the lava chemistry and vesicle-scale textures. As part of a larger ongoing study, we focus here on combining TIR and radar remote sensing to map the textures, structure and emplacement of Holocene silicic domes.
On recently active domes, zones of rapidly changing vesicularity and/or block size can be linked to changes in the extrusion rate, cooling or degassing state of the magma. These regions are prime targets for monitoring due to the increases potential of pyroclastic collapse. However, because of hazardous conditions, direct observations and sampling are commonly impossible. Remote sensing data avoids these hazards and can provide important information on the activity state of a dome. To assess the ability for using these data, we collected measurements on the areal extent, vesicularity, and vertical roughness of silicic lava textures on the rhyolite and dacite domes at Medicine Lake Volcano, CA. The surface percentage of coarsely vesicular pumice was mapped using real-time dGPS and linked to vesicularity maps derived from airborne TIR data. Vertical roughness was measured using a three meter square grid as a base line taking 100 measurements at each of 14 sites. The initial results show that there is a measurable difference in vertical roughness and C-band radar back-scatter between the highly vesicular/scoriaceous regions and the glassy lavas. The areas that contain larger, more interconnected void spaces form smaller blocks, yet have some of the largest RMS slopes/heights due to the presence of extensional zones (crease structures). Also, the scale of roughness is larger on the dacite domes indicating a potential difference due to composition, extrusion rate or cooling.
The next stage of this study is to quantitatively compare the field measurements to the remotely acquired data to determine the accuracy of our models. Once complete, testing is planned on recently-active domes and flows of more mafic composition, preparing for future use of near real-time spaceborne imagery.
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Submitted to: American Geophysical Union Fall Meeting
Date: 1999