A GLOBAL DATABASE OF MAPS SHOWING HYDROTHERMALLY ALTERED AREAS ON VOLCANOES USING ADVANCED SPACEBORNE THERMAL EMISSION AND REFLECTION RADIOMETER (ASTER) DATA

Areas prone to avalanche-induced lahars from hydrothermally altered volcanic edifices were mapped using Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) reflectance data spanning the 0.5 µm - 2.4 µm region and ASTER Global Digital Elevation Model (GDEM) data. This is the first study to set up a global database of hydrothermally altered volcanoes showing quantitatively compiled alteration maps with potentially affected drainages. We prioritized approximately 700 volcanoes based on surrounding population density using the Smithsonian Institution Global Volcanism Program database and LandScan digital population dataset. Using ASTER reflectance data on 100 of the most densely populated volcanoes, we mapped hydrothermal alteration using ENVI image analysis software. Hydrothermal alteration units were reclassified as slopes units (thresholds <30^o, 30^o to 35^o, and >35^o) using GDEM data. ASTER hydrothermal alteration mapping techniques were validated using previously acquired hyperspectral and ASTER data for Mount Shasta, California and Pico de Orizaba (Citlaltepetl), Mexico. We mapped drainages using ASTER GDEM data that show potential flow paths of possible debris flows for the 100 slope-classified hydrothermally altered volcanoes. Potential alteration-related lahar inundation maps for Iztaccihuatl, Mexico and Mount Hood and Mount Shasta in the United States were compiled using "Laharz," a computer inundation model, to show examples of areas that could be affected based on the ASTER alteration-DEM-derived volume estimates of hydrothermally altered rocks and a times-two uncertainty factor associated with the computer model. All image and vector data are available for download from the ASTER Volcano Archive (AVA) for distribution (http://ava.jpl.nasa.gov).

The data provide useful information showing the potential lahar inundation impacts that hydrothermally altered rocks on steep volcanic slopes could pose to populated areas downstream. However, limitations include an unknown frequency of slope failure of altered slopes and depth of ASTER-mapped surface alteration. Thus, the hydrothermal alteration maps should not be used in place of existing volcano hazard maps or studies published by volcano observatories, or agencies responsible for volcano hazard mitigation.