A hillside was seen smoking and emitting the odor of burning hydrocarbons around 9:30 a.m. this morning about one mile west of Arroyo Burro Beach Park. The heat comes from a geological phenomenon in which oil shale deposits embedded in the sedimentary rock are fanned by strong winds, reported the County Fire Department.
This form of naturally occurring spontaneous combustion might be the result of chemically reactive iron and/or sulfur minerals exposed to the air, UCSB geochemist David Valentine explained. Another possibility is that a small landslide provided the friction to ignite the organic-rich shale in the cliff, he said. The wind makes it burn hotter and faster.
Firefighters are familiar with the phenomenon as they have responded to similar calls in the past, including at Hendry’s, as Arroyo Burro is also known, and Rincon, said County Fire spokesperson Mike Eliaison. The fire crew checked this time for possible oil seepage, which was not found, and hydrogen sulfide levels, which were low below the cliff face.
The area has been roped off for safety, and a fire crew is keeping an eye on nearby vegetation. “It’s just one of those geological wonders that happen in our area,” said Eliason.