Mesa Fissures

August 18, 2004

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Provided by: Thomas McGuire, Textbook Author/Educator
Summary authors & editors: Thomas McGuire

The photo above shows earth fissures east of Mesa, Arizona near the Superstition Mountains. The left photo shows the ground just stating to crack and the right photo shows a nearby full blown monster. In some places these fissures extend beneath roads and into housing developments.

When groundwater is withdrawn, the desert sediments compact, and broad valleys can sink several meters. Where basin and range mountain bedrock dips below the surface it often makes a shallow shelf. This shelf can extend many kilometers out from the piedmont and may dive beneath thick sediments at boundary faults. These nick points are where the fissures form.

In spite of the influx of people, water usage is actually decreasing in the Phoenix valley. Drip systems are replacing spray irrigation, and farmland is being replaced by housing developments. In addition, many people use native desert landscaping. Furthermore, water from the Central Arizona Project Canal is supplying Colorado River water to Phoenix and Tucson. But the seven year drought continues and groundwater is still being "mined" from valley aquifers both by farmers and many home owners. So the water table is still going down.

Two principles govern water usage in the southwest. 1. Water flows uphill toward money. 2. Whiskey's for drinkin' and water's for fightin'over.

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