CHAPTER V 

 THE WORK OF SNOW AND ICE 



Snow is perhaps the most common form of ice, but ice on ponds, 

 lakes, and rivers is familiar to all who live where the winters are 

 cold. In middle latitudes the water in the soil and rocks freezes 

 to the depth of several feet in winter. In some parts of the world, 

 too, there are glaciers of which we shall learn in the following 

 pages. In most of its forms ice has some effect on the surface of 

 the land. 



Ice on lakes and ponds. When water freezes it expands about 

 one-tenth of its volume. This is why a bottle full of water breaks 

 if the water freezes. When ice forms on a pond or lake, it expands, 

 just as in a bottle, and crowds upon the shores (Fig. 1, PL XXVII, 

 p. 92). One result is shown in Fig. 2, PL XXVII. 



Suppose a lake frozen over to the depth of a foot or two. If 

 now the temperature falls, as during a "cold snap/' say to 20 below 

 zero (-20 F.), the ice contracts, as most solids do on cooling. It 

 then pulls away from the shore, or quite as often cracks open. The 

 cracks fill with water from below, and the water freezes. After 

 this has taken place, the ice again covers the pond or lake com- 

 pletely. If now the temperature rises, say to 25 F., the ice ex- 

 pands, and as it expands it crowds with great force upon the shores. 

 It is sometimes shoved up on the shore many feet, or even many 

 yards, if the shore is low and sloping (Fig. 1, PL XXVII). If the 

 shore is steep and not too resistant, the ice may be thrust under the 

 soil so as to disturb it, and even so as to overturn trees upon it, as 

 shown in Fig. 2, PL XXVII. 



The water of some lakes is very shallow along the shore, and in 

 such places ice may freeze to the sand, gravel, bowlders, etc., at the 

 bottom and border. When the ice is shoved shoreward it carries 

 these materials with it. Low ridges of sand or gravel, sometimes 



101 



