Avra Valley fissures not a real threat - Tucson Local Media: Marana

Avra Valley fissures not a real threat

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Posted: Wednesday, February 18, 2015 4:00 am

There are four known fissures in the Avra Valley/Marana area that are currently inactive according to the Arizona Geologic Survey. Although fissures can be a geologic hazard, the ones in the area do not seem to pose any imminent threats to homeowners. But that does not mean they are not something to be wary of. 

Fissures are large cracks that develop underground and break open at the surface. According to Michael Conway of the Arizona Geological Survey, the fissures are caused by pumping groundwater in rural areas. 

Since the four fissures in Avra Valley are inactive, the main concern for residents is if a contaminant got into a fissure and into the groundwater. 

“They are essentially conduits to the groundwater,” explained Conway. 

As water is pumped out of the ground, the water table can drop, leading to the surface sinking a bit and the cracks opening up. 

Conway said that fissures are often popular dumping grounds and that it is not unheard of to see 55-gallon drums dumped near them, or even into them. If a toxin were to get into a water supply through a fissure, or any other way, it could render the water undrinkable. 

“That would be of great concern to a hydrologist,” said Conway. “If someone sees someone dumping into a fissure I would encourage them to contact officials.”

While active fissures can cause problems for property owners, the inactive fissures are “not really a threat” according to Conway. Conway said that there were active fissures in Cochise and Maricopa counties that could be potentially hazardous, but as of now that is not true locally. 

“They haven’t changed in years,” said Conway. “In 1988 one opened up by the CAP canal and it damaged it a bit.”

Conway said the damages to the canal were repaired and there has not been  a problem since. Since then there has been no evidence of the fissures causing any damage.

Although the fissures are inactive, their appearance can change. Weather conditions, like the recent rains, can erode the side walls, making the opening at the surface appear bigger. The erosion is just dirt and sediment, and not a widening of the actual fissure. Weather can also cause dirt and debris to fill in the opening, but it has no bearing on the fissure itself, which runs much deeper, up to several hundred feet deep. 

If the fissures were closer to homes or other dwellings the erosion could cause damage, but the Avra Valley fissures are not located near any infrastructure. 

The AGS recently mapped the area, releasing a new map of the four fissures in December and who said that many of them were starting to fill back up with sand and other debris. 

The fissures in Avra Valley are not in highly travelled areas, but that does not mean they could not pose a problem for people and livestock travelling in the area, especially if the shape of the fissures have changed after a storm and a person or animal were to fall into them, but in general the fissures do not cause many problems in the area. 

Two of the fissures are just east of Sandario Road. One of the two is on a parcel of private, fenced land at the northwest corner of Sandario and Twin Peaks roads. The second is primarily underground and is to the southeast of Marana High School near the CAP Canal. 

The other two are more west. One is just west or Trico Road, near Spur Bell Lane. Of the three only this fissure is near any dwellings and would be the most worrisome, especially if it was to become active again. 

The final fissure is in a patch of desert land on the southwest corner of Lambert Lane and Anway Road. 

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