It is rare but it has happened before: one big rock smashing into another one scattered super-heated fragments and ignited a wild fire.
That was the finding of investigators probing the cause of the mid-July Lighthouse Fire in Range Creek.
"It took a long time to feel confident about it, but after talking with geologists and physicists we decided that was it," said Jason Curry, spokesman for the Utah Division of Forestry, Fire and State Lands, one of the investigators.
Curry said that the team was able to trace the point of origin of the fire, and in that place was "a huge boulder" that had recently tumbled down a cliff and collided with another. They found an impact, crater and fresh fragments. At the point of impact there was still fresh powder that could be scattered with a puff of breath.
Curry said he was curious about the seeming coincidence. However, he and the team had other potential causes to investigate.
"We talked with people, checked vehicles, and studied photos taken by people who first spotted the fire," he said. The photos corroborated the team's conclusion that they had the right point of origin.
"We eliminated campfire as a cause, smoking, guns, cutting and grinding, and there was no lightning," Curry explained.
With the usual suspects removed, that left the falling boulder as a potential cause. The investigators checked with the experts at the Utah Geologic Survey, and the UGS found documentation that such impact fires have happened several times.
The physical explanation, in simplest terms, is that a refrigerator-sized boulder in free fall for a few hundred feet packs a lot of kinetic energy, including some heat from friction if it skids from point to point. When it comes to a sudden stop, that energy has to go somewhere.
Some energy goes into sound, some into fracturing the boulder and what it strikes, and the balance into heat.
The Lighthouse Fire was contained before it could spread further than 800 acres. It did not destroy any known archaeological sites in the world-famous canyon.
Reseeding the scars after the Seeley Fire
In other post-fire activities, the U.S. Forest Service this week began dumping tons of winter wheat seed on about 7,000 acres severely burned areas on the Seeley Fire scar of the Manti-La Sal National Forest.
The object is to get the wheat to germinate on steep slopes so its roots will hold the soil in place this winter.That should retain enough soil for native plants to begin recovering the land in the spring.
Mulch is not effective protection against rain erosion on steep slopes. Without roots to hold the soil, it is being washed away by summer rainstorms. Perennial grasses and forbs cannot successfully germinate under these conditions.
Morris Ag Air of Yuma, AZ has four aircraft on the job and has been seeding since Monday. They will apply 187,500 pounds of winter wheat on 6,946 acres at a cost of $254,500.
The winter wheat seeding project is part of the Burned Area Emergency Response effort funded by the Forest Service.
The Manti-La Sal National Forest manages watersheds for people living in eight central/southeastern Utah counties and two western Colorado counties; it cares for 1.4 million acres of wildlife habitat, fisheries in 1,600 miles of perennial streams and 8,100 acres of lakes and reservoirs; it maintains 2,940 miles of road, 430 miles of trails, provides 550 developed campsites for the enjoyment of people who visit the Forest and is the source of 85 percent of the coal mined in Utah.