202 



melting of the surface ice in the lower portion of a glacier 

 sometimes forms streams which cut ice valleys in the glacier. 

 The above considerations help to explain the rough, broken 

 surfaces of such glaciers as shown in Figure 206. Travel 

 across them is difficult and often dangerous. 



PIEDMONT GLACIERS 



Unrestrained by valley walls, glaciers which extend beyond 

 the mouths of their mountain valleys tend to spread (Fig. 210), 

 and may come to occupy a considerable area. As already 

 indicated, when several glaciers descending from neighboring 

 mountain valleys spread out along the base of the mountains, 

 they may unite to form a piedmont glacier. The Malaspina 



Glacier of Alaska is the 

 type example of this class 

 (Fig. 211). It is about 

 1500 square miles in ex- 

 tent (larger than Rhode 

 Island), and its stagnant 

 margin is covered deeply 

 with rock waste which 

 locally supports a dense 

 forest. 



ICE SHEETS 



Some ice sheets or ice 

 caps are rudely circular, 

 and others are irregular in 

 form. The largest attain 

 great size. 



South polar ice sheet. 



Antarctic explorers 



have made known the 



existence of a great ice 



sheet surrounding the 



FIG. 212. Map of Greenland ice sheet. 



