With the Aspen Fire largely contained, wildfire experts this past week began to analyze why this particular fire was so nasty.
First, by Central Sierra wildfire standards, it was in fact a big fire for the type of terrain, firefighters said.
As for its impact, particularly in populated areas such as Mammoth Lakes, people cannot recall anything quite like it—not, anyway, since the Rainbow Fire threatened to burn down the town in August 1992.
“The first thing that made this fire unique is that it essentially burned an area that had already burned in 1939 and had been re-seeded with Ponderosa pine,” said Incident Commander David Cooper.
“That meant the trees were all about the same size and they were very close together, so the fire was able to spread very rapidly. There was often not more than a foot between each tree.”
Second, the fire started at 3,000 feet in an unusually steep river canyon.
Two problems confront firefighters trying to fight fire in such terrain: access (which was difficult in this case), and the extremely steep slopes, which led to extreme fire behavior.
Fire burning on a slope almost never burns downhill; instead the fire tends to run uphill, lighting the fuels in its way as it goes.
In addition, the fire started in a deep river canyon where the winds tend to blow upslope every afternoon and downslope every night.
“Right away, this fire exhibited a high resistance to control,” said Dave Bartlett, a fire behavior analyst assigned to Cooper’s South Central Sierra Interagency Incident Management Team.
“The fire was throwing out a lot of spot fires, burning pine cones and such, as far as a mile in front of the fire,” he said.
Fire is a wild thing. People who study it know it creates its own weather and that certainly was true of the Aspen Fire.
Bartlett said the heat from the fire created its own convection column, which picked up burning pine cones and other fuels and threw them high into the air. The up-canyon wind then grabbed the fuels and flung them out ahead of the fire.
“The burning cones landed, then started their own fires, which then combined to create a bigger fire,” Bartlett said.
That led to another challenge for firefighters, he said.
“We found out very quickly we could not go direct to fight this fire,” he said. “We had to get out in front of it and go indirect and fight if from a ridge or some spot we could stage safely.”
Getting firefighters and equipment to the site proved difficult because there was only one access road near the fire, he said.
That meant it took longer to mobilize crews and equipment to fight the fire than if there had been easier access, although firefighters were on the fire within the first several hours after it was discovered.
“There has been some concerns that we were letting this fire burn too long without resources, but that is inaccurate,” Cooper said.
“There were crews assigned to this fire from the very beginning, including a Hotshot crew and others. There were also 17 other lightning fires on the forest at the same time, which we went after with the same resources. But we knew this fire could be trouble, and it was.”
The terrain forced firefighters to light even more fires near the fire line in an attempt to create a line of already burned fuel adjacent to the hand dug fire line. The technique adds more smoke—and more acreage—but Cooper said it was the only effective way to fight the Aspen Fire.
“We wanted as much depth to this ‘black line’ as possible, so Hotshot crews and other firefighters hand lit a 100- to 200-foot buffer of unburnable ground along the fire line in the trouble spots,” he said.
The smoke also hampered the effort to fight the fire from the beginning to the bitter end, said Matt Mehle, a meteorologist assigned to the fire.
“We were in a stagnant and very persistent weather pattern where an inversion acted like a lid on the smoke from the fire, making it difficult to even see the fire from the air,” he said.
The best information on the Aspen Fire’s exact boundaries came at night, using infrared, he said.
That meant it was hard to use one of firefighting’s most effective techniques—the use of fire retardant and/or water dropped from the air by planes and helicopters during daylight hours.
It was the smoke, in the end, that made the Aspen Fire historic for nearby communities such as Mammoth.
First, the fire was close—about 40 miles southwest of Mammoth.
The smoke was bad for several reasons.
“We could look right up and see the top of Mammoth Mountain from some areas,” said Cooper.
Second, the terrain and weather made the Aspen Fire smokier than usual.
“Fuels, topography and weather all combined to make this fire especially hard on Mammoth and the Eastern Sierra, in terms of smoke,” Mehle said. “The smoke just went right up the canyons and toward you. It was like a gun pointing right at you.”
The inversion layer then trapped the smoke under a persistent high-pressure ridge, adding to more smoky misery for Mammoth, he said.
Air quality is something firefighters like Cooper and his team are increasingly sensitive to in the past few decades.
The Aspen Fire had a tendency to produce unusual levels of smoke and that’s why the fire had its very own air quality specialist assigned to it.
“I was in contact with your air quality specialist every day during our 1 p.m. conference calls,” said John Cook, an air quality specialist. “We were able to predict when it was going to get bad, then let your air quality district know, so they could tell the media and the public what to expect.”
That kind of coordination with communities and air quality districts on the densely populated west side of the Sierra crest, where most fires that affect the Eastside start, is relatively new, said Ted Schade, the Eastern Sierra’s air pollution control director.
“Ten years ago, it was as if there was no one out here,” he said. “That had really changed in the last six or seven years, and we are in much better communication now.”