Use of Geophysics to Aid in Mapping Basalts Relevant to Ground Water Flow and a Landslide Hazard at Hagerman Fossil Beds National Monument
The landslides at Hagerman Fossil Beds National Monument (HAFO) are apparently a consequence of saturation of the loosely consolidated Glenns Ferry sediments. The groundwater system is fed by leakage from unlined irrigation canals lying immediately above these locations on the plateau to the northwest. The main feeder canal to the system is the Fossil Gulch Canal which transports over 60.0 million m3 of water during the five to six month irrigation season. Estimates suggest that as much as 10% of this volume is lost each irrigation season to leakage. Because of canal leakage, as many as four perched aquifers have been created which outcrop on the hillsides within the Monument. Immediately north and east of the most significant paleontological site (the Horse Quarry), nearly 617,000 m3 of seepage occurs annually from numerous location.
In 1994, a seismic refraction study was commissioned by Idaho Power Company to help HAFO upgrade its resource protection program through the identification of additional monitoring well locations. These monitoring wells would also have the potential for serving as dewatering wells. The refraction study was successful in mapping the extent and structure of the Shoestring Road Basalt in the area of the Fossil Gulch Canal and the Horse Quarry. Results of this study suggest that the orientation of the basalt flow funnels the ground waters from the leaking canal towards the cliffs containing the fossil beds.
Paul Michaels, L. Growney, and P. Donaldson. "Use of Geophysics to Aid in Mapping Basalts Relevant to Ground Water Flow and a Landslide Hazard at Hagerman Fossil Beds National Monument" Case Histories of Geophysics Applied to Civil Engineering and Public Policy. Ed. P. Michaels and R. Woods. New York, NY: American Society of Civil Engineers, 1996. 14-26.