VULCANISM 



161 



vapors, some of them poisonous, are discharged along with the hot 

 rock. 



So long as a volcano is active there is likely to be a hollow, called 

 the crater (Fig. 164), in the top of its cone. Craters vary greatly in 



Fig. 164. Sketch of the crater of the cinder cone near Lassen Peak, Cal. 

 The funnel is 240 feet deep. 



size. Some of them are but a small fraction of a mile across, while 

 others are two or three miles across. An opening leads down from 

 the crater to the source of the lava, at an unknown depth. 



From the following accounts of a few active volcanoes, many 

 of the features of volcanic action will be gathered. 



Stromboli. The cone of this volcano is an island four or five 

 miles in diameter, in the Mediterranean Sea, north of Sicily. The 

 cone is built up from the bottom of the sea, and is about a mile high, 

 though but little more than half of it is above the water. About 

 1 ,000 feet below its top there is an opening in the side oi the moun- 

 tain, from which steam issues constantly. At a distance the steam 

 looks like smoke. 



It is sometimes possible to climb up to the crater and look in. 

 Its floor is then seen to be black rock, which is really hardened lava. 

 In this hardened lava there are deep cracks, and from some of 

 them steam puffs out somewhat as from an engine. In other 

 cracks boiling liquid lava may be seen. Bubbles form in it and 

 burst, much as bubbles form and burst in a pot of boiling mush. 

 When they burst, fragments of the lava of which the bubbles are 

 composed are hurled hundreds of feet into the air, and fall on the 

 slopes of the cone. These fragments may be white-hot or red-hot 

 when they are shot out, but they cool quickly in the air, and cease 

 to glow before they have fallen to the surface of the cone. At night 



