High resolution, low altitude aeromagnetic and electromagnetic survey of Mt Rainier

In October 1996, the USGS conducted a high resolution airborne magnetic and electromagnetic survey in order to discern through-going sections of exposed altered rocks and those obscured beneath snow, vegetation and surficial unaltered rocks. Hydrothermally altered rocks weaken volcanic edifices, creating the potential for catastrophic sector collapses and ensuing formation of destructive volcanic debris flows. This data once compiled and interpreted, will be used to examine the geophysical properties of the Mt. Rainier volcano, and help assist the USGS in its Volcanic Hazards Program and at its Cascades Volcano Observatory.

Aeromagnetic and electromagnetic data provide a means for seeing through surficial layers and have been tools for delineating structures within volcanoes. However, previously acquired geophysical data were not useful for small-scale geologic mapping. In this report, we present the new aeromagnetic and electromagnetic data, compare results from previously obtained, low-resolution aeromagnetic data with new data collected at a low-altitude and closely spaced flightlines, and provide information on potential problems with using high-resolution data.