386 



EARTH FEATURES AND THEIR MEANING 



FIG. 412. The Harriman fjord glacier of Alaska, 

 a tidewater variety of dendritic glacier (after a 

 map by Gannett). 



is in such sensitive adjustment to air temperature that a fall or rise 

 of a few degrees only in the average annual temperature of the dis- 

 trict may prove sufficient to fuse many glaciers into one or separate 

 one ice mass into many smaller ones. 



When in high latitudes a dendritic glacier descends in fjords 

 to below the level of the sea, it is attacked by the water in the same 

 manner as are the outlets of Greenland glaciers, and is then known 



as a " tidewater' glacier," 

 which may thus be a 

 subtype or variety of the 

 dendritic glacier (Fig. 

 412). 



The radiating (Alpine) 

 glacier. In the pro- 

 gressive wastings of 

 dendritic glaciers, there 

 comes a time when their 

 dendritic outlines give 

 place to radiating ones. Attention has already been called to the 

 division of the cirque into subordinate basins separated by small 

 rock aretes and yielding a markedly scalloped border (Fig. 394, 

 p. 371). When the ice front retires from the main valley into one 

 of these mature cirques, the now wasted ice stream is broken up 

 into subordinate glacierets, each of which occupies one of the 

 basins within the larger cirque, and these ice streams 

 flow together to produce a glacier whose compo- 

 nent elements radiate like the sticks within a lady's 

 fan (Fig. 408, stage IV, and Fig. 413). 



The horseshoe glacier. As the glacier draws 

 near to its final extinction, it is crowded hard 

 against the wall of the amphitheater in which it 

 has so long been nourished. Up to this stage it 

 has offered a swelling front outwardly convex as a 

 direct consequence of the laws controlling its flow. 

 No longer-amply nourished, for the first time its 

 front is hollowed, and it awaits its final dissolu- 

 tion curled up against the cirque wall (Fig. 408, 

 stage V, and Fig. 414). Practically all the glaciers of the United 

 States and southern Canada are of this type. 



FIG. 413. Map 

 of the Rotmoos 

 glacier, a radi- 

 ating glacier 

 of Switzerland 

 (after Sonklar). 



