COMPILATION OF A DIGITAL GEOLOGIC MAP AND SPATIAL DATABASE FOR NEWBERRY VOLCANO, CENTRAL OREGON: A FRAMEWORK FOR COMPARATIVE ANALYSIS

The geologic map of Newberry Volcano in central Oregon (scale 1:62,500; Sherrod and others, 1995) was digitized and a geospatial database compiled for the area. The digital map consists of 60 geologic units covering an area of nearly 2500 km². The database includes 813 discrete map polygons and available U.S.G.S. 7.5-minute DRGs and 10-meter DEMs. Geospatial data were utilized to determine the aerial extent and distribution of geologic units and other map features. GIS-based analyses show that 73% (1824 km²) of the map area consists of basaltic andesite. Basalt flows and numerous fissure vents and cinder cones (n>400) cover 5% (119 km²) of the area. Undifferentiated sedimentary and pyroclastic deposits, mudflows, and landslide deposits constitute nearly 14% (344 km²) of the map polygons surveyed. Silicic volcanic units compose 6% (147 km²) of the map area, and andesitic units cover less than 1%. Owing to the similarity in aerial extent (>2000 km²), comparable position east of the Cascade volcanic arc, and resemblance in overall morphology, parallels are commonly drawn between Newberry Volcano and Medicine Lake Volcano in northern California. Digital map data from Medicine Lake Volcano (Ramsey and Donnelly-Nolan, 2002) are compared to that from Newberry. The most striking difference is in the aerial coverage of basalt and basaltic andesite at each volcanic center. At Medicine Lake, basalt covers 60% of the mapped area, and basaltic andesite covers 12%, whereas at Newberry basalt covers 5% and basaltic andesite 73%. This variability either represents incomplete discrimination between basalt and basaltic andesite on the published geologic maps for each volcano, or suggests an important compositional distinction between Newberry and Medicine Lake. Development of digital geologic maps and geospatial databases for Cascade volcanoes provides a robust tool for rapid, quantitative comparisons between volcanic centers.