Earth fissures linked to sinking valley in S.AZ

Posted at 6:46 PM, Feb 13, 2016
and last updated 2016-02-13 22:37:07-05
The valley surrounding a southern Arizona city is sinking.
The Casa Grande Dispatch reports geologists determined the valley around Eloy is 20 feet lower than it was 50 years ago, and earth fissures are likely to blame. 
Earth fissures are believed to be created by quickly depleting groundwater causing land to cave in. Six new Arizona Geological Survey maps show these hazards in southern Arizona, including study areas east of Picacho Peak. Dozens of earth fissures have been reported in the area. 
No human deaths have been linked to earth fissures, though the survey has been mapping them since a horse fell into one and died in 2007.
"If you stop drawing on the groundwater table, we would anticipate at some point the subsidence would stop," said survey geological extension service chief Michael Conway.
Earth fissures open the possibility of potential groundwater contamination, among other hazards.
"A concern that we have is that contaminated fluids can get into these fissures and actually propagate very, very quickly into a groundwater aquifer," Conway said.
Fissures are not the same as sinkholes, which can also be caused by the rapid depletion of groundwater and are tied to dissolving minerals.
The agency says it will monitor and map earth fissures as they appear.