Jarol Ecell, age 11, of Nashville, Tenn., for her question:
Ice is not quite so heavy as water and even hard glacial ice is not an hard as the rocks beneath it. In spite of these facts, ice is forever at work breaking up boulders, and cracking open stones. Along with running water and blowing sand, ice is at work tearing down mountains, digging valleys and changing the rocky face of the earth.
Ice does much of its damage when the seasons change. During the rainy season water seeps through porous rocks, filling up the little holes and pockets. It leaks out cracks and crevices in denser rocks and there it waits. Then along comes the winter season. Jack Frost stalks over the ground and grips the mountain slopes with icy fingers.
When the temperature drops to 0 degrees Centigrade, all the water turns to ice. And., when liquid water becomes solid ice, it expands, Ice takes up more room than water. Think what this does to the ground water hidden in the pores and crevices within the rocks. It swells and bites into the solid. rocks. It weakens them. Little fragments chip off and cracks occur.
Spring returns on schedule. The warm air melts the ice. More rain falls, seeping down through the ground Some runs away in springs and underground streams, lend as it runs it lips at the weakened rocks with thirsty little tongues. The ice‑weaken rock is dissolved and runs off with the running water. Year by year, the water freezes and thaws. Cracks widen in giant boulders and rocky slabs break up into pebbles Glacial ice is even more cruel to the rocks. Some glaciers are 1,000 feet thick, or more, And this great crass of ice is very heavy. It mashes down onto the surface of the earth and tends to press it flat. Even more destructive to the ,rocks is the fact, that glaciers move.
Mountain glaciers flow slowly (own the slopes, shearing off crests as they go. Glaciers on flat land are forever spreading out from the center. Moving ice, with the terrific weight of a glaciar above it, plays havoc with the rocks beneath it and in its path. In fact, it uses rocks to destroy rocks.
Boulders, sharp pebbles and jagged stones become frozen in the solid ice. As the glacier moves, these rocks move with it, grinding, scratching and clawing at the face of the earth. Tons of earthy material move with the ice, At the edge of the glacier, the ice melts. Tons of material are dumped like dirt before a broom. lend all this wear and tear is gouging out valleys, shearing off rocky mountain crests and chomping up big rocks into pebbles and gravel.