You have probably been told about the huge masses of ice that exist at the north and south poles today. You may also h., have heard that thousands of years ago great tongues of ice stretched southward from the north as far as Britain and northern Europe, and that millions of years before many of countries of the southern hemisphere were similarly affected by an Ice Age as these periods of extremely harsh conditions are called. But how do these tongues of ice occur what effects can they have on the face of the Earth?
It has already been mentioned that some of the water falling from the sky may do so as snow rather than rain. This is particularly likely to happen at the tops of mountains and in the regions closer to the north and south poles, where the temperatures are generally lower. Of course, we quite often wake up on a cold winter's morning to find everything outside shrouded by a glistening, soft, white mantle, but our snow soon melts again. In some parts of the world, however, such as in Greenland or the Himalayas, not all of the snow which falls in the winter is melted during the short, cool summer months and the snow tends to build up into snowfields. This is the first condition necessary for the formation of the frozen sculptors of our planet, the glaciers. As the snow builds up in the snowfield, it becomes compacted into bluish ice rather than the familiar, white snowflakes.
The glaciers often flow down-hill from the snowfield where they are formed and only come to rest when the rat of melting of the ice-fronts, or snouts, as they are often called is greater than the amount of ice which can be provided by the snowfield.
When the snout of a glacier meets the sea as often happen in Alaska, for example, great chunks of ice may break from the parent glacier by a process called calving to send an iceberg out into the icy seas. If you have seen photographs of these great blocks of ice you will know what an impressive sight they are, but it is as well to remember that the mountain of ice which you see rising grandly out of the water is only the tip of the iceberg, and that nine-tenths of it is under water. It is not surprising then that it was an iceberg that was responsible for the tragic sinking of the great steam ship which was thought to be unsinkable, the Titanic. She foundered and sank very quickly on her maiden voyage with the loss of over 1000 lives after a collision with an iceberg.