Months later, remnants can ignite
Several times during the latest wind event, local fire departments were called out to Mountain Center. One of the calls was about midnight. Smoke was seen and it appeared that a fire was starting.
Upon arrival, firefighters discovered patches of wood and duff causing the smoke and heating up.
“These calls were actually for smoldering fires,” wrote Charles Wentz, forester for the U.S. Forest Service’s San Jacinto Ranger District. Essentially, these were remnants of the Cranston Fire in July and August.
Both Wentz and Gregg R. Bratcher, unit forester and division chief for Riverside County Fire Department, affirmed that this is not unusual within an area of a massive fire.
After the fire is first contained and then controlled, the clean-up efforts emphasize eliminating the threat that the fire may expand. Yet, there may be islands within the burned area that are not extinguished or simply smolder. Since they are surrounded by burn-scar surface, these pose little threat to grow.
On the Hill, because the duff is so deep after years of accumulating pine needles, leaves and other fuel debris, the duff will continue to burn slowly beneath the surface. Occasionally, roots retain heat and burn — rather smolder — for months.
The strong Santa Ana winds arrive and provide air and oxygen to these small hot spots and ignite new flames, which are visible above the surface.
“With the super-duff layer, it can burn under the dirt as well as above,” Bratcher stated. “Even with infrared, we can’t detect the subsurface heat. Eventually, it will go out.”
“My best guess is that these were areas of hold-over heat from the Cranston Fire that gained enough energy, due to low, single-digit relative humidity and high winds, and ignited,” Wentz said in the email. “It is possible for something to remain hot for months, but conditions have to line up perfectly for a flare-up to occur. In the case of the McCall Park flare up, it was a combination of friction and very low relative humidity.”
As an example, Bratcher referred to the direction to campers, when ready to depart, to stir the fire embers to ensure all are extinguished.