Snow, Ice, Avalanches, and Glaciers - Mountain Geography: Physical and Human Dimensions - page 152

FIGURE 4.5 Nakaya's diagram showing the consistent relationship between cloud conditions and ice
crystal form. (Nakaya, 1954, courtesy of L. R. Dexter and K. Birkeland.)
The Seasonal Snowcover and Old Snow
Upon reaching the ground, snowflakes quickly lose their original shapes as they become
packed together and undergo metamorphism (Seligman 1936; Bader et al. 1939; de
Quervain 1963; Colbeck 1983). Snow, then, displays continual change during formation,
falling, and accumulation on the ground, until it eventually melts. Snow may form in
the atmosphere at any latitude but, in order to maintain its identity, it must fall to the
Earth in an area with temperatures sufficiently low to prevent it from melting. Most
snow melts within a few days or months of the time it falls (referred to as the seasonal
snowcover ), but snow can remain year round depending on the amount received and on
climatic conditions. Polar areas receive very little snow, owing to their extremely low
temperatures, but what does fall is preserved with great efficiency. On the other hand,
snow may persist even in areas where temperatures are above freezing if sufficient