NEWS RELEASE: Revised Earth Fissure Maps for Cochise, Maricopa and Pinal Counties released.
Immediate Release – 2/03/2016
Tucson, AZ – The Arizona Geological Survey (AZGS) continues to map, monitor, and inform the public regarding earth fissures in south-central and southeastern Arizona. Six freshly revised earth fissure maps are now available for parts of Maricopa, Pinal and Cochise Counties. A single new earth fissure map for just east of the Picacho Mountains in Pinal County was issued.
Updated earth fissure study area maps, include: Luke and Chandler Heights in Maricopa County; Picacho and Friendly Corners (3 map sheets) and Santa Rosa Wash in Pinal County; and North Sulphur Springs Valley and Dragoon Road study areas in Cochise County.
The maps and digital data are available at the Natural Hazards of Arizona viewer. Individual fissure study area maps are online at the Arizona Geological Survey’s Online Document Repository. A Google Earth .kmz file is available for viewing the fissures on Google Earth.
All new or revised earth fissure maps employ a base map displaying National Agriculture Imagery Program aerial photography and, when available, a local subsidence map, provided courtesy of the Arizona Department of Water Resources.
A new fissure line category (yellow lines) portrays select fissures as confirmed that were otherwise not mapped by AZGS’ fissure mapping team. These include fissures mapped by reliable sources and those identified on multiple aerial photographs. Previously, if fissures could not be identified during field checks, the fissure was reported as unconfirmed.
Besides posing a threat to infrastructure, fissures are frequently used for illegal dumping of tires, appliances, construction debris, manure and other sundry items. Because fissures extend downward towards the groundwater table, they represent a potential conduit for surface runoff to contaminate aquifer resources.
AZGS’s earth fissure mapping team will continue to monitor existing earth fissures and map new ones as they form. AZGS geologists collaborate with hydrologists from the Arizona Dept. of Water Resources to better understand where and when fissures will occur, and with local environmental and geological engineers on ways to mitigate and minimize the impact of earth fissures.
Earth fissures are cracks, seams, or separations in the ground produced during 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 urban and suburban centers encroach on 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.