A River of Black Sludge With Debris Flooding Through Arizona

A video of a river of fast-moving, dark sludge with ash and soot flooding through a bike trail in Arizona seemed unreal.

But it is real. On July 15, Cañada del Oro Wash in Arizona flooded with the black sludge after a minor storm.

Authorities from Pima County report that the debris flow has not caused any death or injuries.

Why does this happen?

According to the official Pima County Twitter Account, the frightening scenes are the result of the recent Big Horn Wildfire that has swept the area in the past weeks.

After the wildfires, it is likely that " debris flows" are formed: the deadly fast-moving waters that are created from even a small amount of rain from the area where the fire happened.

The wildlife has caused the ground to be barren, charred, and unable to absorb moisture. This leads to devastating floods even with little warning.

Normally, rainwater is absorbed by the soil, preventing incidences of flash floods. But the wildfires cause the soil to dry up so water flows freely even with little rain.

USGS California Water Science Center warned that "fast-moving, highly destructive debris flows triggered by intense rainfall are one of the most dangerous post-fire hazards."

The Center cited that in Southern California, even as little as 7 millimeters of rainfall in 30 minutes leads to debris flows.

Debris flows can be deadly. In 2018, 13 people died from debris flow after the Thomas Fire.

After wildfires, floods are a thing to look out for. Floods can happen at any time and anywhere altering the course of water flow.

Roads can easily turn into rivers. The risk that such a catastrophe happens can take years following the major wildfire.

Bighorn Fire

For the first time since the fire, members of media were invited to view Mt. Lemmon for the first time on Monday, July 20.

The Bighorn Fire, the lightning-caused active wildfire burned more than 48, 377 hectares of Sta. Catalina Mountains. As of July 15, 89 percent of the fire has been contained.

Capt. Dan Leade of Mt. Lemmon Fire Department announced that Mt. Lemmon, still green and full of life in some areas despite being scorched in some places. He considered this a big victory for the department as no structures or homes were lost during the fire. Unlike the Aspen fire two decades ago, 300 cabins and business establishments were burned down.

Although the fire containment was a relief for residents, tourism business owners are still worried because the road up the mountain is still closed for the public until November 1. Mt. Lemmon is a popular recreational ski area.

Pima County Sheriffs Department Public Information Officer Deputy James Allerton said that the road remains closed because parts of the fire are still crossing the roadway. The department also said they will close some parts of the forest for safety reasons even if the roads open.

"They're going to be fewer places to go to up here and we want everybody to come up here safely when they do come," said Allerton.

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