Snow feeds glacier in the same way that rain feeds the rivers. For glaciers are frozen rivers – following, creeping, draining, tumbling off the mountains, wherever temperatures are low enough to keep the snow frozen throughout the year. They are driven by gravity, down the slopes, off and away from their mountain origins and their careless movement accounts of most of the complex variety of shapes and patterns into which they can evolve. So they are much more than just great white barriers; glaciers are active components of the landscape, powerful, just little mysterious and often very beautiful.
Where snow fall accumulates on a massive scale, great ice sheets can build up – with the two largest blanketing the central parts of Antarctica and Greenland. These are among the world’s most desolate environments, with flat or gently rolling white surfaces reaching to and beyond every horizon. The ice begins to develop more character where it flows as glaciers, down the slopes and away from the ice sheets. The scale can be tremendous; there are glaciers over 100km long in Antarctica, and the longest glacier outside the polar regions is one just 75 km long in the Karakoram mountains of Pakistan and that was very beautiful.