FIELD MAPPING IN THE 21st CENTURY: COMPARISON OF CONVENTIONAL FIELD MAPPING AND SATELLITE-IMAGE-BASED MAPPING: AN EXAMPLE FROM OWENS VALLEY, CALIFORNIA, A TECTONICALLY ACTIVE AND ARID REGION IN THE USA

Geologists go out into the field to explore, explain and to map the rock record. In recent years, modern space-based satellite technology revolutionized the spatial resolution of digital elevation models and images of the earth’s surface. It is now possible to map geological contacts precisely prior to entering the field, but this raises the question whether traditional field mapping is becoming obsolete?

In order to answer this question, we chose the Piute Creek alluvial fan in Owens Valley as a test region as part of an undergraduate student field-mapping campaign. Without any prior field-mapping experience, we mapped all geological and geomorphological contacts and structuresvisible on satellite images from NAIP with a resolution of 0.6 m and topographic maps of 1:10000 scale produced from a 30 m - SRTM digital elevation model. Satellite images were digitally enhanced using different color schemes and filters used for mapping.

We were able to map precisely the location of any linear feature such as stratigraphic contacts, faults, joints, but had difficulties addressing the rock types remotely. We then spend 4 weeks in the field to map the previously identified active tectonic offsets of the Piute alluvial fan. We were able to confirm that 4 lineations on the satellite image were indeed fault scarps. Other fault scarps were clearly visible in the field, but could not be recognized on satellite images. On the satellite image we found other lineations that resembled fault scarps, but they turned out to be fumaroles in the field. The channel of Sabies Creek was offset near the apex. The offset was visible on the satellite image and was determined to be 7 to 8 m. The offset was found to be 7.2 meters in the field, consistent with previously published studies. The spatial resolution of the digital elevation model limits the resolution of small structures, which implies that some of the small vertical offsets can only be identified in the field.

We conclude that satellite images are a new essential tool to (1) prepare for field work, (2) to precisely map geological contacts and (3) to precisely locate oneself in the field without the use of GPS instruments. In the future, effective field mapping will be based on a judicious combination of preparatory satellite-based mapping and focused field mapping campaigns.