LASER POSITIONING AND 3-D DIGITAL MAPPING OF WESTERN OKLAHOMA EVAPORITE KARST

Cavern morphology and distribution in three Western Oklahoma evaporite karst systems were mapped using laser/global positioning systems. Portions of Jester Cave, the Corn Caves, and the Nescatunga cave system, all located within the gypsiferous Permian Blaine Formation, are being investigated in association with a series of surface geophysical studies in order to develop a cavern detection methodology. The Nescatunga system in particular has a history of highway collapse hazards. Digital mapping of cavern voids makes use of a reflectorless laser rangefinder with internal inclinometer linked to a digital compass and referenced to global positioning system receivers positioned outside the cavern entrances. This is a standard surveying technique for use under bridges and beneath heavy tree canopies. A series of control stations are laser-located along a cavern traverse at approximately 20 meter intervals and marked by mounted reflectors. Fifty or so additional laser positions of cavern floors and walls are taken as offsets from each station. Positioning data is downloaded onto a laptop computer and visualized with GIS and CAD software, enabling a real-time geo-referenced image of cavern shape to be developed. Sub-decimeter scale accuracy is achieved and verified by reoccupation of stations and by positioning from two or more GPS locations at different entrances. The resulting digital 3-D map of a portion of each cavern system investigated is used in interpretation of results of surface geophysical imaging techniques (discussed elsewhere in this session), both in order to provide “ground truth” for the geophysical surveys and to refine the methods for use in cavern detection in surface-inaccessible sites.