Setback battling CZU Lightning Fire as flames moved underground

On Friday the repopulation of evacuated areas in Santa Cruz and San Mateo counties continued. Firefighters have been able to push containment of the CZU August Lightning Complex Fire to 27%. But amid the progress, there was setback Thursday night into Friday.
Experts said extremely dry conditions below the surface allowed the fire to spread one-thousand acres along the only escape route available.
“Often times [when] a fire is burning a tree trunk or the stem of a shrub, it can follow the stem down the scrub into the root system,” said Dr. Kate Wilkin, a fire ecologist at San Jose State University’s Department of Biology.
She said flames move underground, as opposed to along the floor of a burn area.
Thursday as firefighters used controlled burns to limit the supply of fuel, flames from the CZU mega-fire went south. Dry underbrush and roots allowed the fire to spread 1,000 acres. This wildfire has torched 83,133 acres across Santa Cruz and San Mateo counties.
“An area that has been a challenger because of the typography and a challenge with all the homes, here’s yet another challenge for us when we’re constructing our lines,” said Cal Fire Section Chief Mark Brunton. Added Dr. Wilkin, “Overall, it’s a phenomenon that’s hard to see and hard to fight. Because you can’t see it. It’s underground.”
Another challenge for those on the front lines, the danger of fire-weakened trees toppling to the ground. In one case, a tree fell, splitting a family’s home in two.
“There’s a lot of the fire-weakened trees in there. We’re in there assessing that. And developing a strategy on how we’re going to address that issue,” said Brunton.
Firefighters say damage assessment of roads and bridges in areas being repopulated is 70% complete. They urge residents returning home to show caution, since fire down below could weaken footing, leading to injury.
“This type of ground fire can be really dangerous for firefighters. Because if you step on an area and the ground underneath is not there anymore and it caves in, you can fall into an area that is very hot from the fire. It can also be dangerous for residents and people who are returning to their homes,” said Wilkin.
She points to the case in the “Rim Fire” in Yosemite in 2013. Due to a lack of rainfall, the underground fires in that natural disaster weren’t tapped out until the following year.
Cal Fire has infrastructure groups working to mitigate hazards faced by returning residents.