21 July 2022
Mudflows at the site of the Pipeline Fire in Arizona
In the middle of June 2022 the so-called Pipeline Fire broke out in Coconino National Forest in Arizona. With a total surface area of 10,737 hectares, this was a large and damaging wildfire. The cause is as yet to be officially determined; last week a man was convicted of starting a fire close to his camp, less than 100 m from where the fire started.
It is well-documented that wildfires leave the landscape vulnerable to mudflows, some of which can be deadly. On 15 July 2022 heavy rainfall triggered mudflows in the burnt area of the Pipeline Fire. Arizona Game and Fish has posted a dramatic video of one of these to Youtube:-
There is a further excellent video in an article on the mudflows in the Arizona Daily Sun. The video is about halfway through the article. The same piece provides useful detail on the nature of the flows:-
The boulder field seen at Copeland Wash is the result of the watershed’s natural alluvial fan “unraveling,” explained Coconino County deputy manager Lucinda Andreani. Above the Timberline neighborhood, there was a place in the Copeland Wash that naturally fanned out and allowed water to slow down, spread out, and drop sediment.
But during the extreme flows of Friday’s flood events, this fan could not contain the water coming off the burn scar. Instead of spreading out, the water eroded into and “channelized” the fan, turning it a source of new sediment — and boulders up to five feet in diameter — to be washed downstream.
The image below shows the aftermath of the mudflows in the area of North Copeland Lane (location: 35.313, -111.554):-
The scar of the mudflows is visible in Planet Labs imagery captured on 19 July 2022:-
Further mudflow events are likely through the summer rainy season from this, and of course other, wildfire scars. The estimated cost of mitigation of mudflows in the aftermath of the Pipeline Fire alone is estimated to be $20-30 million.
Planet Team (2022). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/