Improved earth fissure maps for Cochise and Pinal Counties, Arizona

Tucson. Earth fissures continue to be a growing problem in Cochise County as new fissure areas have been identified in the past two years. Earth fissure maps for two such areas, Croton Springs, Willcox Basin, and Elfrida, Douglas Basin, are now available as free PDF downloads at the Arizona Geological Survey (AZGS) Document Repository. AZGSs earth fissure map format has been substantially revamped to make the maps easier to use and to include subsidence maps for valleys hosting earth fissures. The new map format incorporates a high-resolution, air photo base map compiled from 1-meter resolution National Agriculture Imagery Program imagery (2010), and ground subsidence maps from the Arizona Department of Water Resource InSAR (Interferometric Synthetic Aperture Radar) satellite land subsidence monitoring program. Subsidence, as shown on the InSAR inset map, is measured in centimeters. The Picacho-Friendly Corners area, Pinal County, and Three Sisters Buttes, Cochise County earth fissure study area maps are reissued in this new map format as well. Arizona Geological Survey geologists mapped about 1.6 miles (~8,800 feet)of continuous and discontinuous earth fissures in the Elfrida (~7,100 feet) and Croton Springs (~1,700 feet) areas. In Cochise County, earth fissure maps are available for the following areas: Dragoon Road Three Sisters Buttes Bowie-San Simon Elfrida Croton Springs The Dragoon Road and Bowie-San Simon maps will be reissued in the new format in the near future. The Sulphur Springs North earth fissure study area just north of Willcox in Cochise County remains to be mapped. AZGSs Earth Fissure Viewer shows the footprints of all previously mapped fissure study areas and provides links to free, downloadable PDFs. A Geographic Information System (GIS)file showing the locations of mapped earth fissure traces in Arizona should be available for download shortly. Besides posing a threat to infrastructure and livestock, fissures are an illegal dumping ground for tires, appliances, construction debris, manure and other sundry items. Because the fissures are believed to extend down to the water table, earth fissures represent a potential threat by serving as a conduit from surface runoff contaminating groundwater resources. The AZGS Earth Fissure Mapping Program will continue to update maps as earth fissures grow and new ones form. AZGS geologists will begin focusing on ways to predict where and when the fissures will appear and work with local building officials and engineers on way to mitigate existing earth fissures to minimize their impacts. BACKGROUND INFORMATION Earth fissures are cracks, seams, or separations in the ground c differential land subsidence that accompanies extensive groundwater harvesting. The earliest appearance of fissures in Arizona was near Eloy in 1927. Individual fissures range in length from hundreds of feet to miles, and in width from inches to tens of feet. Currently, geoscientists believe that fissures initially form at the groundwater table and then propagate upwards hundreds of feet to the surface. Because fissures are commonly oriented perpendicular to local drainages, they are capable of capturing surface runoff. In-rushing waters may result in rapid erosion of sidewalls and gully development causing dramatic and sudden changes in fissure geometry -- length, depth, and width. Earth fissures are a geologic hazard in the arid valleys of central and south-central Arizona. As population centers expand into subsiding areas of basins/valleys, residents and structures are placed in closer proximity to fissures. Property owners are encouraged to 1) set structures as far away from fissures as possible, and 2) prevent water from entering fissures. Reports of earth fissures are confined to Cochise, Maricopa, Pima, and Pinal counties in central and south-central Arizona. In 2007, AZGS released 1:250,000-scale planning maps of the four counties showing the approximate locations of earlier reported earth fissures. These earth fissure planning maps are available free, online at the Earth Fissure Center at www.azgs.az.gov/efc. AZGS is charged by state statute with mapping earth fissures in Arizona.