Arizona Geological Survey Releases First Detailed Earth Fissure Maps
by Mimi Diaz and Bryan MacFarlane, Arizona Geological Survey
On 23 April 2008, the Arizona Geological Survey (AZGS) released new detailed maps that show locations of earth fissures in Maricopa and Pinal Counties. As a result of an earth fissure that catastrophically re-opened during a storm in August 2005, the state legislature charged AZGS with mapping earth fissures throughout Arizona for the purpose of disclosure in real estate transactions.
Prior to this statute, there was a lack of information available to the public about earth fissure locations, and many property owners were unaware of the presence of earth fissures and their impacts. Now, armed with the new maps from AZGS, stakeholders have increased ability to make informed decisions about land use.
Earth fissures are linear cracks in the ground that form at depth and work their way up to the surface as a result of the lowering of the ground due to over-pumping of groundwater. Fissures often make their first appearance as a narrow crack in the surface that can drastically widen into gully proportions in a short amount of time (even as short as a single storm event) with the addition of water, thus they are constantly changing. Earth fissures range in width from less than an inch to several feet, and in length from tens of feet to miles.
Earth fissures have been reported in four counties: Pinal, Maricopa, Cochise, and Pima. AZGS divided the fissure locations into 23 study areas and prioritized the mapping order by likelihood of development. The first two of these individual study area maps, which contain the locations of earth fissures that AZGS geologists have identified, measured, and recorded, are the Chandler Heights and Apache Junction study areas. These new maps display street-level detail locations of earth fissures, accurate to within twelve feet.
The new earth fissure maps are available as free, downloadable PDFs and GIS shapefiles on the AZGS website (www.azgs.az.gov), and a searchable interactive map (hosted by the Arizona Department of Real Estate) is available online as well (http://azmap.org/fissures).
AZGS is currently completing mapping in the Luke, Toltec, and Picacho study areas, which are slated to be released next. The websites will be continuously updated as the individual study areas are completed and released.
Since the legislation was passed in September 2006, in addition to mapping the earth fissures, AZGS has been working closely with stakeholders and state and local agencies by serving as an information resource, distributing educational materials, providing public outreach, and by helping other agencies address concerns about the societal impacts of earth fissures as they crop up. If your agency has questions, ideas, or concerns, please feel free to contact Todd Shipman in Tucson (todd.shipman@azgs.az.gov) or Mimi Diaz in Phoenix (mimi.diaz@azgs.az.gov).