If you see a huge plume of smoke south of the Valley, it's a huge hay fire burning in the area of Riggs Road between Interstate 10 and Sun Lakes to the east.
The smelly smoke was blowing into Ahwatukee.
The Gila River Fire Department is on the scene, but based on video from the Penguin Air & Plumbing News Chopper, the fire did not appear to be threatening any structures.
Sun Lakes is about 30 minutes southeast of Phoenix.
While firefighters will keep an eye on the situation, they likely will let the fire burn itself out. That is fairly standard with this kind of fire, which can burn for days.
"Hay fires usually occur within six weeks of baling, but they may occur in hay several years old," according to the National Ag Safety Database." Fire can occur in loose hay, small bales, large bales or in stacks."
Excessive moisture is usually to blame for such fires.
"Freshly cut forage materials are not dead," NASDOnline.org explains. "Some respiration continues and a very small amount of heat is produced."
This sets up perfect conditions for bacteria to grow. That growth process generates heat, often deep in the hay bales or stacks.
"The thermophilic bacteria and the heat they generate convert the hay to a form similar to a carbon sponge with microscopic pores. In this form and at the high temperatures present in heated hay, the material combines readily with oxygen. It can self-ignite in the presence of air and its tendency to burn is almost unbelievable."
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