Sherrie Carter, age 9, of Winston Salem, North Carolina, for her question:
How does melting snow form icicles?
When the snow falls, it spreads a soft white carpet on the ground. It drapes a clean cover on the roofs and hangs rows of fluffy feathers on the trees. The whole world looks like a fairyland. But sooner or later the snow melts. The ground becomes a soggy mess of slosh and mud. But there may be one lovely sight left to see. And that is around the roofs where the melting snow forms into fringes of glistening icicles.
Sometimes icicles form around a roof, even before the snow on the ground starts to melt. This seems like a lovely miracle, because you do not suspect that the soft, fluffy snow and the hard shiny ice are related to each other. But they are. And because of this, the snow can cause a row of hanging icicles around the roof. Actually, snowflakes are made of ice tiny crystals of ice too small for our eyes to see. Millions of them are arranged together to make each single snowflake. They are arranged in lacy patterns with tiny spaces between them. The pattern of crystals and airy spaces plays tricks with the light tricks that make the snow look white.
Ice, as you know, is related to water. Water, of course, freezes to solid when it gets cold. When the ice warms up, it melts back into water. If the same water gets cold again, it may freeze back again into solid ice. This is about what happens when the melting snow hangs a fringe of icicles on the roof. Everything depends on a certain temperature called the freezing, point of water.
This temperature is 32 degrees Fahrenheit. When the weather gets this cold, it forms frost and the water outdoors changes to ice or at least some of it does. The water stays frozen as long as the weather stays this cold or gets colder. But if the temperature rises, even part of one degree warmer than freezing, the ice begins to melt. This sometimes happens, even on a frosty day. And the likely place is a roof. Inside the house we turn up the furnace. The walls and ceilings and even the roof get warmer warmer than the freezing weather outdoors.
If the roof is covered with snow, the little crystals of ice in the snowflakes melt and turn to water. The water runs down and starts to drip around the edges of the roof. Out in the cold, it soon freezes back to solid ice again. The dripping
How does melting snow for Friday, April 24, 1970 water freezes into glassy fingers of ice. As more snow melts on the roof, more cold water drips down the same paths. It slithers over the smaller icicles and freezes solid. Drip by drip the melting water freezes and the icicles grow fatter and longer.
The key to this miracle is the freezing point of water 32 degrees Fahrenheit. Icicles form when the temperature switches back and forth from a little warmer to a little cooler than 32 degrees Fahrenheit. This can happen in snowy weather when the days are warmer than the nights. Then we sometimes find icicles hanging on the trees. But most often it happens when the snow on a roof is warmed by the furnace inside the house.