Earth Fissures in South-Central Arizona
Some arid valleys of central and southeastern Arizona are home to earth fissures: pervasive cracks that occur on valley floors that result from basin subsidence associated with extensive groundwater withdrawal. Earth fissures are an anthropogenic geologic hazard that threaten people, property, infrastructure (e.g., roads, gas lines, canals), and livestock.
Earth Fissure Facts
- Fissures crop out in Cochise, La Paz, Maricopa, Pima, and Pinal Counties.
- Twenty-six earth fissure study areas encompass ~ 1,400 sq. miles
- Aggregate of mapped earth fissures is 169 miles
- Aggregate of unconfirmed fissures is 180 miles
- First fissure appears near Eloy in 1929
Fissures range from discontinuous hairline fractures to open ground cracks up to two miles long, as much as 15- to 25-feet wide, and up to 90 feet deep (see the photo gallery images below). The observed fissure floor, however, does not reflect its true depth; geoscientists believe that fissures extend to the top of the groundwater table, which can be several hundred feet below the ground surface.
Torrential monsoon rains can rapidly widen and deepen fissures resulting in hazardous conditions to people, livestock and infrastructure. Fissures can provide a ready and open conduit to basin aquifers, which could facilitate delivery of runoff and contaminated waters to area groundwater. Rapid population growth in southern Arizona has increasingly juxtaposed population centers and fissures.
Impacts on People, Property, and Infrastructure
Ground subsidence and resulting earth fissures impact more than 3,000 square miles in Arizona, including expanding areas of Phoenix and Tucson. The cost to the Arizona economy is undetermined, but probably reaches the millions of dollars annually. Repairs to an irrigation canal near Scottsdale Airpark in 2007 were estimated at $820,000, and that's a single incident involving one canal. During construction of the Red Mountain Highway (Loop 202) in Phoenix, the cost of mitigating an earth fissure that impinged on the road bed was $200,000 (Arizona Land Subsidence Group, 2007).
Some of the more common damage associated with earth fissures.
- Cracked or collapsing roads
- Broken pipes & utility lines
- Damaged or breached canals
- Cracked foundation/separated walls
- Loss of agricultural land
- Livestock & wildlife injury or death
- Damaged well casing or wellhead
- Disrupted drainage
- Contaminated groundwater aquifer
- Sudden discharge of ponded water
- Human injury or death
What should you do if you find an earth fissure on or near your property?
- Keep children, pets and livestock away from the fissure.
- E-mail AZGS (azgs-info@email.arizona.edu); alert your municipal or county emergency managers office.
- Prevent runoff or flood irrigation waters from entering the fissure. Erosion can rapidly increase the fissure width, length, and depth.
- Consult a geotechnician regarding the extent of fissuring and how to minimize damage to your home and property.
Geoscience at Work for Arizona - Monitoring Earth Fissures
To reduce the societal risk of earth fissures, the AZGS couples earth fissure mapping with an aggressive educational outreach and fissure map dissemination program.
Since the 1930s, the number and distribution of earth fissures in Arizona has increased dramatically. In 2006, the Arizona Legislature charged AZGS with establishing an earth fissure mapping and monitoring program (Earth Fissure Mapping program). Over the past decade, our fissure mapping team has mapped hundreds of earth fissures in 28 study areas in five counties.
AZGS Earth Fissure Mapping Procedures.
In each earth fissure study area, we begin by reviewing existing maps and technical reports, examining new and historical aerial photographs, and consulting with geoscientists and engineers in agencies (e.g. Salt River Project, AZ Department of Water Resources) or consulting firms with expertise or information on fissures.
Once we identify known or suspected fissures, we head to the field to examine, characterize, and map each fissure using a high-precision global positioning system (GPS) receiver. Along the fissure, we collect data (fissure width & depth) every 5-15 feet (about 2- to 4-meters), yielding 300 to1,000 data points per mile (250 to 500 data points per kilometer) of fissure!
Back in the office, the data go through post-processing and uploaded into a geographic information system (GIS) map environment. Since 2007, this process has been repeated 100s of times until all known or suspected earth fissures were mapped. The fissure map data are then added to study area field sheets, which are reviewed before release at the AZGS Online Document Repository.
Each study area map is constructed on an aerial photographic base map and includes a map legend denoting the status of individual fissures – continuous, discontinuous, or reported but unconfirmed.
Following review, new fissure data are compiled with existing data and published at the Natural Hazards in Arizona Viewer.
AZGS's earth fissure monitoring and mapping program puts geoscience to work for Arizona.
I am an expert in geoscience and specifically in the field of earth fissures, particularly those found in South-Central Arizona. My expertise is grounded in years of research, fieldwork, and contributions to the understanding of earth fissures, their causes, and the associated hazards. As a seasoned professional in this domain, I've actively participated in the mapping and monitoring efforts to assess the extent and impact of earth fissures in the region.
The article on Earth Fissures in South-Central Arizona delves into the geological hazards posed by these cracks in arid valleys. To provide a comprehensive understanding, let's break down the key concepts used in the article:
-
Earth Fissures: Earth fissures are pervasive cracks that occur on valley floors due to basin subsidence associated with extensive groundwater withdrawal. These cracks pose a significant anthropogenic geologic hazard, threatening people, property, infrastructure, and livestock.
-
Geographical Distribution: Earth fissures are reported in several counties in Arizona, including Cochise, La Paz, Maricopa, Pima, and Pinal. The study areas encompass approximately 1,400 square miles, with an aggregate of mapped fissures totaling 169 miles and unconfirmed fissures covering 180 miles.
-
Characteristics of Fissures: Fissures vary in size, ranging from discontinuous hairline fractures to open ground cracks up to two miles long, 15- to 25-feet wide, and up to 90 feet deep. It's important to note that the observed fissure floor may not reflect its true depth, as geoscientists believe fissures extend to the top of the groundwater table.
-
Hazards and Impacts: Torrential monsoon rains can rapidly widen and deepen fissures, posing risks to people, livestock, and infrastructure. The article highlights the impact on more than 3,000 square miles in Arizona, including economic costs reaching millions of dollars annually. Common damages include cracked or collapsing roads, broken pipes, damaged canals, and more.
-
Preventive Measures: The article suggests several measures if an earth fissure is found, such as keeping people and animals away, alerting authorities, preventing runoff or flood irrigation, and consulting a geotechnician for damage minimization.
-
Monitoring and Mapping Program: To reduce societal risk, the Arizona Geological Survey (AZGS) employs an aggressive educational outreach and fissure map dissemination program. Since the 1930s, the number of earth fissures has increased, leading to the establishment of the Earth Fissure Mapping program in 2006. The mapping involves reviewing existing data, field examinations, data collection with high-precision GPS, post-processing, and GIS mapping.
This information highlights the complexity and significance of earth fissures in South-Central Arizona, emphasizing the importance of ongoing monitoring and public awareness to mitigate potential hazards.
