Hunt for Hidden VolcanoesHunt for Hidden VolcanoesCritical facilities, such as nuclear power plants and high-level radioactive waste repositories, must be constructed at sites with very low geologic risk. In May 1996, my company performed a survey using a 12-channel, L1, C/A-code differential GPS (DGPS) unit interfaced to a cesium-vapor magnetometer. Our mission was to map buried volcanoes as part of our risk assessment of the first proposed U.S. high-level radioactive waste repository -- Yucca Mountain, Nevada.
Volcanic eruptions are considered a potential hazard because Yucca Mountain is located within an active basaltic volcanic field. Yet, because sedimentation in the basins adjoining the mountain is also very recent, additional volcanism is hidden by young alluvial deposits. We must know the distribution of these buried volcanoes to adequately analyze the volcanic hazard.
A five-person team headed out into the field to map the area. During the fieldwork, the system made real-time differential corrections to the position data and sent them, by way of an RS232 cable, as an NMEA string from the DGPS unit to the magnetometer, which stored the data with the magnetic measurements. After 10 days, the team mapped 120 square kilometers, collecting more than 95,000 data points on more than 150 kilometers of survey traverse lines. Without GPS, the survey would have taken 10 weeks and yielded lower resolutions.
Afterward, we downloaded the combined DGPS and magnetometer measurements into a geographic information system for postprocessing. We made some notable geologic discoveries, including the final stages of inundation and burial of two young volcanoes; a completely buried volcano, implying more persistent volcanic activity than indicated by surface exposures; and a north-northwest trending magnetic anomaly.
Because debate continues about whether the probability of volcanic eruptions is enough to relocate a site, we plan to conduct more geophysical surveys on Yucca Mountain and better map the region's geology.