You may wonder what does the overpumping of groundwater from the aquifer have to do with the occurrence of earth fissures.
Groundwater pumping is associated with land subsidence and fissures. Hydrologists and geologists draw a direct connection between overpumping of groundwater and the subsequent occurrence of land subsidence and earth fissures. There is no debate about that connection.
To understand why it is helpful to get a better mental picture of what a groundwater basin would look like if you could actually see it. What you would see underground is a mixture of sand, gravel and other sediments with water filling all the spaces between all the individual pieces of sand and gravel.
When we pump groundwater out of the ground we are draining all the water from those spaces between all the individual grains of sand and rocks. When all that water drains out of the sand and gravel there a millions of empty spaces left behind. Over time the pressure from the soil above this drained sand and gravel pushes the sand and gravel closer together. As the sand and gravel is compressed its volume shrinks and the overlying earth sinks. This sinking is called land subsidence. Parts of the Sulphur Spring Valley are currently subsiding at a rate of 4-5 inches per year!
So what does all of this have to do with fissures -- those pesky cracks in the ground that keep closing our roads during the monsoon season? The diagram below tells the story.
Again take a mental journey deep into the aquifer all the way to the bottom where the sand, gravel and water end and you run into solid rock. That rock is called bedrock and it keeps all that water in our groundwater basins from draining down deeper. Fissures occur at the earth's surface but the underlying cause of the fissure lies at the bottom of the aquifer -- that is the bedrock. When there are abrupt changes in the depth of the underlying bedrock in an aquifer there will be more subsidence on the side with the deeper bedrock and less subsidence on the side with the more shallow bedrock. Large cracks (aka fissures) open up as the deeper soil shrinks and pulls away and down from the more shallow soil.
These fissures are not going away any time soon. In fact, they will only get worse as we continue to pump more water out of the aquifer then is going into the aquifer and the bigger that overdraft the worse the subsidence and fissures will become.
Here are a couple of excellent sources that provide a detailed explanation of earth fissures and document the current subsidence and fissure issues in eastern Cochise County:
Geologic Hazards: What You Need to Know About Earth Fissures by Christopher Wannamaker
2021 Monsoon Rains Reactivate Earth Fissures In Cochise County, Arizona, Arizona Geology E-Magazine
