One Year After Fire, the Heat Is Still On

As brush fires go, the blaze last summer on a remote hillside in the Los Padres National Forest northeast of here didn’t amount to much. Firefighters quickly beat down the three-acre brusher and then stuck around to watch for flare-ups and hotspots.

The problem is that the hotspots didn’t cool down.

“Normally, the heat on the ground goes away after a while,” said Allen King, a U.S. Forest Service geologist based in Goleta. “This time, it didn’t.”

No one knew why hot gases continued to spew from cracks in the ground. Since the Aug. 21 fire, the hot spots in the Dick Smith Wilderness have become a geological oddity.

A few days after the fire, a forester brought in a candy thermometer -- “because that’s what he had” -- to measure the heat, King said. The device could measure temperatures up to 400 degrees Fahrenheit. The readings went off the end of the scale.

More sophisticated thermometers were brought to the steep, dusty slope about 20 miles north of Carpinteria.

In the cracks at the surface, temperatures were as high as 200 degrees. Eighteen inches down, the readings soared to 450. Eleven feet down, the top reading was 584.

“The burning temperature of paper is Fahrenheit 451,” said Jim Boles, a mineralogist at UC Santa Barbara. “It was hot enough to have started that fire.”

There are theories, but the source of the heat is still uncertain.

“It seems very strange to me,” King said. “I’ve talked to a lot of people. There’s nothing like it anywhere else.”

In the months that followed, King, Boles and Robert Mariner, a hydrologist and chemist with the U.S. Geological Survey in Menlo Park, Calif., made several visits to the site, which is a parching 3 1/2 -hour hike in from California Highway 33, the lonely 58-mile road over the coastal mountains between the Ojai and San Joaquin valleys.

They noticed that the fire had burned atop a 17-acre swath of broken ground where a landslide had occurred, probably five to 10 years earlier. The hot spots in the ground were concentrated along a three-acre strip in the upper half of the slide area. The burn area was at the top of the slide.

“We know what it isn’t,” Mariner said. “It isn’t a volcano. It isn’t geothermal. It isn’t an oil or gas leak.”

“Apparently, there is some sort of chemical reaction,” King said.

He said that when the landslide churned up the ground, it seems to have unearthed iron sulfide minerals and exposed them to oxygen in the air.

The reaction between the minerals and oxygen releases heat, Mariner said. “In some mines, waste heaps heat up enough to start timbers burning. We suspect that the same sort of reaction is going on.”

Mariner said the reaction probably continued until enough heat was generated to ignite scattered concentrations of carbonaceous material in the ground.

“It’s coal-like material, icky brownish black,” he said. “It’s low grade, but it does burn.”

The scientists said the fire apparently then spread to the surface, igniting the grass and brush.

But Boles said the triggering mechanism was still not that clear, and he stressed that further study was needed before scientists could say definitively what happened last summer on the forest slope.

“There aren’t that many sulfides there,” Boles said. “There’s not that much carbonaceous material. How do you get enough of that stuff to create that much heat?”

In the meantime, officials are keeping the precise location of the hot spots a secret.

“We don’t want people in there, because we don’t know what all the risks are yet,” King said.