CHAPTER VI 

 GLACIERS 



CHARACTERISTICS OF GLACIERS 



Formation of snow fields and ice fields. When the water 

 vapor of the air condenses at temperatures below the freezing 

 point, it is usually as ice crystals, which form snowflakes. 

 Above an irregular surface in the air all points in which have a 

 temperature of 32 Fahrenheit (the isothermal surface of 32), 

 condensing water vapor accordingly usually forms crystals of 

 ice, many of which become snowflakes, while below it the 

 moisture condenses as water, and forms cloud particles or rain- 

 drops. This surface of 32 Fahrenheit is encountered at vary- 

 ing altitudes. It is high near the equator (15,000 to 18,000 

 feet above sea level), and is at sea level in certain polar regions. 

 In many places, as in northern United States, for example, 

 its position varies notably with the seasons; it is higher in 

 summer and lower in winter. In sufficiently high places in 

 low latitudes and over wide areas in high latitudes, it is at or 

 near the surface during much or all of the year. In such situ- 

 ations more snow falls in the colder months than is melted and 

 evaporated in the warmer ones. The line above which snow 

 is always present is called the snow line. While the position 

 of the snow line is influenced chiefly (1) by temperature, it 

 varies also with (2) the amount of snowfall, being lower when 

 the snowfall is heavy and higher when it is light, and (3) the 

 character of the topography, for some situations favor the 

 gathering of snow and afford protection against the sun, 

 while others do not. In general it does not depart greatly 

 from the summer position of the isothermal surface of 32. 



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