New Project Maps Location of Earth Fissures in Arizona

Prescribed by law, maps show home buyers areas to avoid

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The Arizona Geological Survey is embarked on a legislatively mandated earth fissure mapping project to provide developers, Realtors, prospective homeowners and others ready access to maps showing the locations of earth fissures in populated counties of the state. According to HB 2639 (2006) earth fissure maps must be made available to the public in both printed and electronic format on request, and updated on a five year basis. The Arizona State Land Department will provide on-line public access to the maps.
This summer AZGS released individual, 1:250,000 scale, earth fissure planning maps of Cochise, Maricopa, Pima, and Pinal counties that are now available on-line. The maps show all currently mapped or reported earth fissures. Compiling and releasing the maps are step one in the process of preparing highly detailed fissure maps to be completed over the next few years. Also available on line is a 25-page report, Earth Fissure Mapping Program: 2006 Progress Report, describing the steps taken to produce the maps and noting future AZGS mapping plans.

Michael Conway, chief of AZGS Geologic Extension Services, says, “We refer to the 1:250,000 maps as planning maps; they are designed to guide us in developing the finer scale mapping.” He says, however, that the larger scale maps contain all the earth fissures from previous fissure studies they were able to compile. The finer, 1:24,000 maps will be prepared for specific priority areas.

Conway says , “We have a list of 23 priorities areas within the four counties. We are finishing up Chandler Heights, and that will be coming out shortly. ... We are charged with providing the data to the Arizona State Lands Department. It then has 90 days to get the information out.”

The maps identify areas with known fissures. Each area is assigned a name, and the maps are indexed with the designated names of the fissure study areas to facilitate communication among scientists, local governments, real estate agents and the general public.

Study areas were ranked on three criteria: 1) potential for rapid development of communities; 2) the presence of known or reported fissures; and 3) areas where rapid land subsidence has been reported.
Pinal County has the greatest number of study areas because it has the highest number of reported fissures. Also new construction in the area is rapidly encroaching on fissure zones. Maricopa County has fewer study areas; its fissures are generally located in rural and other areas unlikely soon to be developed. An exception would be along border with Pinal County where developers are rapidly constructing new homes.

AZGS acquired high-resolution recent aerial photography from Maricopa and Pinal counties, and older, lower resolution photography of all known earth fissure areas from the U.S. Geological Survey through a University of Arizona hosted web service. Professional quality GPS equipment and data processing software were purchased to ensure that all disclosure mapping meets exacting standards of accuracy and precision.
The maps will not provide a person with complete assurances that an area will not be threatened by future earth fissures. Conway says, “Just because we have not found fissures in an area doesn’t mean fissures cannot appear. We anticipate as we go through these 23 studies finding fissures that have not been previously mapped. It is not at all impossible that new fissures will develop over time, especially if we continue to withdraw water at a rapid pace from the subterranean aquifers.”

Arizona is not the only state undertaking an extensive earth fissure mapping program, although it is striving for special recognition in the field. Conway says, “We are trying to take a leadership role in doing some of the mapping and establishing protocols for mapping earth fissures.”

Noteworthy accomplishments include developing standards and procedures to ensure earth fissure mapping accuracy, coordinating among involved agencies, and working with affected stakeholders to assist them to deal with the maps when released. The project has provided an opportunity to prioritize mapping areas, evaluate mapping at different scales and levels of detail, and develop consistent standards, protocols and methodologies.

The AZGS mapping program is generally viewed as a long overdue project. Most existing fissure maps were made before the GPS system was available. Further, the existing maps were not digital nor at adequate scales needed by developers and local building officials for detailed planning purposes. Some known fissures have never been mapped at more than regional scale.

The intent of the law requiring the availability of the maps and information is to raise home buyers’ awareness about fissures and make information about them more generally available. Coming from out of state, many home buyers are unaware of the earth fissure threat. Home buyers also have been stymied by the lack of readily available information.
Copies of the planning maps and report are available at: http://www.azgs.az.gov/

“Tremendous” Response to Fissure Maps

On June 4 the Arizona Geological Survey placed its earth fissure county maps on-line at www.azgs.az.gov. Since then, according to Michael Conway, chief of AZGS Geologic Extension Services, “A tremendous amount of attention is being paid to them.” Responses vary. For example, Conway says that Maricopa County might have 20 or 40 downloads per day, although if a news article about fissures appears the number might spike to about 700 downloads per day.

Following is the total downloads of the various earth fissure county maps from June 4 to Oct. 31: Maricopa County - 14587; Pinal County - 9851; Cochise County - 2216; Pima County - 2541. Also, there were 8442 downloads of the Earth Fissure Mapping Program report.

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