ENVIRONMENT

A not-so-grand canyon has opened in the Arizona desert. How? Why? (Forbes)

Learn more about the forces that create earth fissures with our activity.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• The big crack in the Arizona desert is called an earth fissure. What is an earth fissure?
  • Earth fissures are associated with land subsidence, the process of a large area of land lowering in elevation. “Earth fissures start out as small cracks … They grow and widen from surface water flowing into the crack, eroding material from the sides.”

• The big earth fissure in Pinal County is a result of aquifer drawdown or aquifer depletion. What is aquifer depletion?
  • Just what it sounds like. Aquifer depletion describes the process by which people pump more water out of aquifers than can be replaced by rain or snow.
  • In Pinal County, aquifer depletion empties the porous sandstone aquifer whose pockets hold the local groundwater. Aquifer depletion means that eventually, the brittle sandstone collapses at its weakest points, causing land subsidence, sinkholes, and earth fissures.

• What are some reasons the aquifers in Pinal County might be depleted? How does your community use groundwater?
  • Communities use water for many, many purposes.
    • drinking
    • hygiene
    • recreation, such as swimming pools and artificial lakes
    • maintenance of gardens and lawns
    • agriculture
    • industry or manufacturing

• Can land lost to subsidence and earth fissures be reclaimed?
  • No. Once the soil and sedimentary rock collapse on themselves, land generally remains subsided.

• Are there dangers associated with earth fissures?
  • Yes. Much like sinkholes, earth fissures “have destroyed pipelines, roads, canals, and even homes.” This infrastructure damage can cost millions of dollars.
  • Earth fissures also pose a danger to livestock and drivers who might fall into the fissure.
  • “Another issue with earth fissures is that [they] creates an easy place for groundwater to become contaminated. Pollutants, pesticides, and other chemicals can simply make their way deep into the earth and enter an aquifer by flowing into the crack. The infiltration process that normally would purify the water is essentially skipped where a fissure exists.”
  • Elevation and slope change created by land subsidence and earth fissures alter the natural drainage paths on flood plains. This may increase flooding that impacts homes and businesses.

• Does the big earth fissure in Pinal County pose any significant risks?
  • No. “Thankfully the crack is in the middle of the desert and likely not a harm to humans as long as no one attempts to walk or drive up to the crack.”

• The title of this study guide alluded to the REALLY big fissure in northern Arizona. Is this how the Grand Canyon formed?
  • NO!
    • The Grand Canyon is much grander. (The Pinal County fissure is about two miles long and about 30 feet deep. The Grand Canyon is 277 miles long and 6,000 feet deep.)
    • The Grand Canyon formed through much grander geological forces. (The Pinal County fissure was created through aquifer depletion. The Grand Canyon was created through tectonic uplift.)

TEACHERS TOOLKIT

Forbes: An Enormous Crack Just Opened Up In The Middle Of The Arizona Desert

Nat Geo: Groundwater Movement activity

Arizona Department of Water Resources: Land Subsidence in Arizona

Owlcation: Geologic Hazards: What You Need to Know About Earth Fissures