Understanding a 'crown fire'

From his office in Reno, Gary Zunino could see a brown column of smoke rising more than 50 miles to the southwest -- evidence of the kind of wildfire thought to be the most destructive to wilderness and the most frustrating to firefighters.

In the trade, they're known as "crown fires.'' They leap from treetop to treetop, dancing through a canopy well beyond the reach of ground crews. Even aerial drops are often ineffective; crown fires burn so hot that water and fire retardants can evaporate before they do much good.

"They're virtually impossible to stop until they run out of fuel,'' said Zunino, director of the University of Nevada's Fire Science Academy.

"The big challenge is to keep the fire from getting up there in the first place.''

The U.S. Forest Service describes the fire that has destroyed more than 220 structures in the South Lake Tahoe area as a crown fire. It's an especially treacherous fire to fight because it's in rugged terrain, produces cascading volumes of blinding smoke and is consuming tall, tinder-dry trees that have been weakened by drought or killed by insects.

Evergreens like the pines and firs in the area can be saturated with pitch and "literally explode,'' Zunino said.

-- Steve Chawkins