William Arrington, age 13, of La Range. Ga.,, for his Question:
Why does snow stay can the mountain tops?
In Georgia, a deep winter snowfall is rare. But in Canada, and some Of our northern states, the ground is covered with snow all through the winter. Frost and new snowfalls build a crusty layer that does not melt until the spring warms the air. But even at the equator, lofty mountains keep their snowcaps all through the year.
The earth, as we know, is warmed by the beaming sun, and the top of a mountain is nearer to the sun than a deep valley. It is logical to suppose that a mountain top gets more heat than a valley, and you would think that the snow that falls upon it would soon melt and. Come gushing down the slopes. But the facts contradict this reasonable idea.
Imagine a journey westward across the prairies in summer time. The scorching sun beats down, dusty whirlwinds dance among the sage and the air feels as hot as an oven. Suddenly you see a fluffy cloud bank on the western horizon. Soon, you hope, there will be some sheltering shade in the sky. But not at all. Those distant clouds are the snowy shoulders of Rocky Mountain National Park.
Lofty mountains in Africa and save of the Andes peaks close to the equator are also crowned with snow throughout the year. The highest peaks are more likely to be snowcapped, no matter haw hot it is on the level ground at their feet. This is because the air near the ground is much warmer than the air aloft; and the higher we go, the cooler it gets.
The radiant energy of the sun does not give up its heat as it passes through the empty reaches of space. It gives up only a small faction of heat as it passes down through the filmy atmosphere. But some of this radiant energy is turned into heat when it hits the solid ground and the shiny surface of the sea.
The land and water are heated by the sun, but very little of the sun's heat warms the air. However, the sir can be warmed by the earth and the sea. And it is the bottom layer of sir which gets this warmth. This is why the air is warmer near the ground and why it gets cooler the higher we go. The warm air near the surface may pass on same of its heat to the air above it, and some of the warm surface air is lifted aloft in updrafts. Hut the warm air never rises high enough to melt the snag on the tops of the world's tallest mountains.
At the top of a high peak, the air is almost always below freezing. The clouds shed snow instead. Of rain, and the snow becomes chilled into a frozen mass which is actually a glacier. This mass of frozen snow acts like a slow, slow moving river. As it gets thicker, the edges creep down the slopes of the mountain. When they reach the lower levels of warmer air, the frozen snow melts which explains Why we always find chilly streams gushing down the sides of a snowcapped mountain.