412 MOUNTAINS, EARTHQUAKES, VOLCANOES, GEYSERS 



small fragments of rock called volcanic ash or dust, gases, 

 and vapor are hurled out. The outstreaming lava flows 

 around the crater and on cooling solidifies and builds up into 

 a gently sloping mound or cone. Some of the rock frag- 



B. F. Loomls. 



FIG. 279. Mt. Lassen in eruption. 



ments also fall around the crater and help to build up the 

 cone. The smallest rock fragments are hurled far into the air, 

 where they are caught by the winds and carried long distances. 

 The hot gases and vapor are also blown far and wide, and some 



