Reminiscent of a horror movie where a big black gloopy river of sludge moves towards you in a haunting manner, residents of Pima County in Arizona witnessed a similar terrifying event on July 15th.
A jet-black river of sludge in fact flooded through a riverbed in the U.S. state following a wildfire in the area.
As county officials and experts from the U.S. Geological Survey (USGS) state, the event likely happened because wildfires sometimes affect how rainwater moves over land.
From wildfires to black rivers
Pima County officials posted the video of the sludge river, known as a sediment sludge, on their Twitter account in mid-July, following up with why this bizarre event likely happened.
A wildfire in the Cañada del Oro Wash is most likely the reason this occurred. As the USGS states, earth typically absorbs rainwater, however, after a fire happens most soil is stripped bare and if any rainfall, heavy or light, occurs soon afterwards, there's nothing left to absorb that water.
Floods can happen anywhere and at any time. But did you know wildfires increase flood risks? It’s true. Wildfires like the Bighorn Fire leave the ground charred, barren, and unable to absorb water.#FloodsFollowFires— Official Pima County (@pimaarizona) July 16, 2020
So, picking up all the burnt debris along its path, the rainwater turns into a dark, charred-looking sludge that moves as quickly as a regular river.
"It takes much less rainfall to trigger debris flows from burned basins than from unburned areas. In Southern California, as little as 7 millimeters (0.3 inches) of rainfall in 30 minutes has triggered debris flows."
Who had this on their 2020 hellscape bingo card? pic.twitter.com/fUNvIVS7aw— Official Pima County (@pimaarizona) July 16, 2020
Luckily, no casualties or disastrous damage were caused because of this particular sediment sludge. However, even though it's an eyesore, if the muddy, murky waters make their way into our dams, they can threaten drinking water as the thickness of the debris-filled water can block up pipes, as per Science Alert.