IMPLEMENTATION OF GROUND-BASED LIDAR, TOTAL STATION, AND GPS IN AN ADVANCED GEOPHYSICAL STUDY OF BASALTIC CINDER CONE MORPHOLOGY, FOUR CRATERS VOLCANIC FIELD, OREGON

The processes by which cinder cones and their associated lava fields originate, grow, and deform are complex. In studying the morphology of the Holocene Four Craters volcanic field in south-central Oregon, our research team from the University of Oregon and Woods Hole Institute found the data resolution of aerial photographs, topographic maps, and space-borne DEMs to be inadequate for fine-scale mapping and descriptions. To provide higher topographic resolution and advanced geophysical descriptions, we employed GPS, Total Station, and ground-based LiDAR in the morhphological study of the Four Craters cinder cones, lava field, and adjacent normal faults. The ground-based LiDAR collected data for analysis of features of different scales, such as clast-size distribution on the cone slopes, outcrop textures, and lava flow/fault interactions. The Total Station and GPS were used to precisely locate LiDAR scans in topography previously unresolved, and as tools for geologic mapping.

The Four Craters volcanic field originated from four ~200m high cinder cones that are aligned in a SE to NW trend, with multiple lava flows emerging from the base of each cone. The four cinder cones rest at the center of a SE to NW trending graben that is consistent with a broader regional trend of faulting. The Four Craters lava flows appear to have postdated faulting, as flow directions indicate the fault scarps acted as barriers to flow. However, minor lobes on the edges of the Four Craters lava field appear to be offset and stretched across smaller cracks in alignment with the larger normal faults, suggesting continued syn-eruptive faulting. Complementary LiDAR and Total Station surveys were completed on a portion of both major bounding normal faults to describe the lava flow/fault interaction. Each cinder cone exhibits a varying degree of cone rim failure, with intact mounds of scoria, aglutinate, spatter, and bombs found rafted on top of the predominantly a'a lava flows up to 0.5 km from the source vents. Rafted tephra mounds off the southernmost cone were the focus of a comprehensive LiDAR, GPS, and Total Station survey, allowing for reconstruction of the volume of the original cone material.