Why must the man stop and build a second fire?

The man has to start a second fire because he falls through the snow and wets himself up to his shins. Cursing his luck, he knows that starting a fire and drying his foot-gear will delay him at least an hour. Unfortunately, clumps of snow from the spruce tree above fall down and snuff out the fire. Though building a fire in the open would have been wiser, it had been easier for the man to take twigs from the spruce tree and drop them directly below on to the fire. Each time he pulled a twig, he had slightly agitated the tree until, at this point, a bough high up had capsized its load of snow. It capsized lower boughs in turn until a small avalanche had blotted out the fire.