Crown fire is a royal flame for firefighters
June 26, 2007
SOUTH LAKE TAHOE ” Some fires race across grasslands and others burn miles of brush. But for firefighters, the most difficult are those that leap from treetop to treetop.
The blaze that has destroyed so much so quickly near Lake Tahoe is the latter ” the kind known as a “crown fire” to the frustrated professionals who struggle to fight them, no less understand them.
Crown fires can burn as hot as 1,500 degrees Fahrenheit ” so hot that water dropped on the flames from aerial tankers can evaporate before it does much good. Ravaging the forest canopy, crown fires produce cascading volumes of thick, choking smoke. In many cases, they roar on so intensely that firefighters are left with no choice but to watch.
“When it gets into the trees all we can do is back off,” said Fire Capt. Brian Eagan, a 23-year veteran of the California Department of Forestry. “There’s nothing we can do.”
Eagan’s crew saved a neighborhood of million-dollar homes near South Lake Tahoe. On Monday, he stood on a steep ridgeline nearby and surveyed a crest where trees had burned like matchsticks. Towering flames had whipped across the ridge, dancing between the treetops.
“They’re nothing more than standing logs now,” Eagan said.
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Winds on Monday calmed, helping the legions of firefighters. As many as 1,400 firefighters are on the scene or en route.
The previous night, though, the winds were gusting up to 35 mph and the flames were unstoppable, said Capt. Tim Allison of the Tahoe-Douglas Fire District.
“The idea is to keep the fire out of the crowns, but with wind ” there’s nothing you can do with 200-foot flames. You run to get ahead of the line using bulldozers, natural barriers, hand tools, people. We threw it all at it.”
From the University of Nevada, Reno, Gary Zunino could see a column of brown smoke looming over Lake Tahoe, more than 50 miles away. The director of the university’s Fire Science Academy, he was blunt about the chances of even the best-equipped fire crews prevailing against a raging crown fire.
”They’re virtually impossible to stop until they run out of fuel,“ he said. ”The big challenge is to keep the fire from getting up there in the first place.“
In the Tahoe area, conditions were ripe for a crown fire: hot days, high winds and plentiful underbrush. Some trees were tinder-dry, weakened by drought or dying from insect infestations. The plentiful ponderosa pines and Douglas firs in the region are sometimes so pitch-saturated that they ”explode,“ Zunino said.
The threat of a catastrophic blaze was so well-known in the area that the U.S. Forest Service had mounted an aggressive, pre-emptive effort to thin the fuel from 38,000 acres in the Lake Tahoe Basin.
In a sense, the fire started more than a century ago. When the Comstock mining boom swept into Nevada, vast slopes in the Tahoe region were clear-cut for timber to brace tunnels and shafts and build mining towns like Virginia City. The U.S. Forest Service estimates that 90 percent of the area’s trees are less than a century old.
Over the years, trees were planted too close to one another, with little regard for ecological diversity. Swift fire-suppression saved the forest but also allowed for volatile underbrush to accumulate over many decades.
On its Web site, an environmental group called the League to Save Lake Tahoe has warned about a ”high risk“ of crown fire.
“It would undoubtedly devastate homes, and runoff from the scorched lands could contribute to the degradation of Tahoe’s famed clarity,“ said the group, whose Keep Tahoe Blue bumper stickers are frequently seen around the state.
Scientists know that the average crown fire travels about 1 mile an hour, that flames shoot into the sky at least twice as high as the trees they consume, and that the resulting wall of fire can settle on an object in its path for as long as 1 minute — a lifetime in such extreme heat, said Marty Alexander, a scientist with the Canadian
But even with exhausted crews carving wide firebreaks out of the woods, stopping the fire is still an elusive goal. Crown fires have been known to leap across lakes.
Eagan suggested that some forces are just too big to battle.
”Sometimes Mother Nature says, `I’m sorry, but today I’m going to have it my way,’“ he said.
– Times staff writer Eric Bailey contributed to this report.