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Show 77 fire lines (trenches) dug around the burn and with retardant dumped from airplanes. But if a hot, dry wind is blowing, fire not only spreads along the ground, it leaps across the tops of t r e e s . "At that point there's no way to contain i t , " Karen says. "You just wait for it to burn i t s e l f out, hoping that rain or snow will soon f a l l ." Fire crews s t i l l battle valiantly to keep the fire from spreading to danger areas, but Nature has made the decision that the fire will not be suppressed. The Heart Lake f i r e in Yellowstone stopped after burning 5,000 acres, which seems like a large area. By contrast, tvio Alaskan fires in the same year consumed 37*000 and 73#°0O acres. In the past, the majority of forest fires were people-caused, by careless campers viho didn't put out their f i r e s , by cigarets, sparks from cars or t r a i n s , children playing viith matches, or arson. With public education, the number of people-caused fires decreased dramatically. Today half of a l l forest fires are caused by lightning, especially the dry lightning vihich s t r i k e s in the West and is not followed by rain. Clouds can be so high that raindrops evaporate before reaching the ground. A severe thunder-and-lightning storm can s t a r t a dozen f i r e s simultaneously, Lightning strikes may smolder for days, and then, vihen donditions become right, they flare and spread. For years a l l forest fires were suppressed. Because of i t s belief that the nation's resources had to be preserved, the Forest Service followed a policy of s t r i c t fire control. In the 1970s that policy began to change. A Forest Service publication s t a t e s , "In our quest |