Aerogeophysical Measurements Reveal Collapseprone Hydrothermally Altered Zones At Mount Rainier Volcano, Washington

New helicopter-borne electromagnetic and magnetic data, combined with detailed<br>geologic mapping, reveal that appreciable thicknesses of mostly buried altered rock lie<br>mainly in the upper west flank of Mount Rainier identifying this as the most likely source<br>for future large debris flows capable of reaching now densely-populated areas. Most of the<br>summit, central core and upper east side of the volcano are free of significant volumes of<br>weak, highly-altered rock and are at relatively lower risk of collapse. In addition, the lack<br>of highly altered rock lies in the volcano's core may impede collapse retrogression and limit<br>volumes and inundation areas of future debris flows. High-resolution geophysical and<br>geologic observations yield an unprecedented view of the 3-D distribution of collapse-prone<br>altered rock at Mount Rainier, and have potential application to hazardous volcanoes worldwide.