THE APPLICATION OF GPS AND GIS TO MAP VOLCANIC FIELDS AND DEFINE MAGMATIC HISTORIES AROUND MT. MCLOUGHLIN, OREGON

In-depth geologic mapping and petrological studies have been completed on many of the large stratovolcanoes throughout the Cascades, such as Mts. Rainier, Mazama, and Shasta. Only limited analysis has been completed, however, on the smaller edifices and flows between these cones. In this study, in collaboration with Franklin & Marshall College, two 1:24000 USGS quadrangles adjacent to Mt. McLoughlin, Oregon were mapped: Willow Lake and Rustler Peak. The accuracy and precision of the field mapping was enhanced by the use of GPS technology, used in concert with hard-copy maps. The subsequent definition of geologic unit extents was completed using GIS technology, allowing for a clearer determination of relative flow ages and edifice volumes. Through an application of previously-published regional eruption ages, this in turn allowed for a first-order determination of cone-building rates from these smaller, peripheral vents. Crystallization textures observed in these flows were also correlated with distance from eruptive centers. This allowed for the determination of patterns relating post-eruptive crystal growth rates to flow volumes and distance travelled. For the purposes of simplifying future field-mapping in this region, GPS tagging was also used to document deviations from the most recently published topographic maps of these two quadrangles.