CHAPTER X 



THE RISE OF MOLTEN ROCK TO THE EARTH'S 

 SURFACE 



VOLCANIC MOUNTAINS OF EJECTED MATERIALS 



The mechanics of crater explosions. If we now turn from 

 the lava volcano to the active cinder cone, we encounter an entire 

 change of scene. In place of the quiet flow and convulsive move- 

 ments of the molten lava, we here meet with repeated explosions 

 of greater or less violence. If we are to profitably study the 

 manner of the explosions, considering the volcanic vent as a great 

 experimental apparatus, it would be well to select for our purpose 

 a volcano which is in a not too violent mood. The well-known 

 cinder cone of Stromboli in the Eolian group of islands north of 

 Sicily has, with short and unimportant interruptions, remained in 

 a state of light explosive activity since the beginning of the Chris- 

 tian era. Rising as it does some three thousand feet directly out 

 of the Mediterranean, and displaying by day a white steam cap 

 and an intermittent glow by night, its summit can be seen for a 

 distance of a hundred miles at sea and it has justly been called 

 the " Lighthouse of the Mediterranean." The "flash" interval 

 of this beacon may vary from one to twenty minutes, and it may 

 show, furthermore, considerable variation of intensity. 



For the reason that the crater of the mountain is located at 

 one side and at a considerable distance below the actual summit, 

 the opportunity here afforded of looking into the crater is most 

 favorable whenever the direction of the wind is such as to push 

 aside the overhanging steam cloud (Fig. 111). Long ago the 

 Italian vulcanologist Spallanzani undertook to make observations 

 from above the crater, and many others since his day have profited 

 by his example. 



Within the crater of the volcano there is seen a lava surface 

 lightly frozen over and traversed by many cracks from which 

 vapor jets are issuing. Here, as in the Kilauea crater, there are 

 open pools of boiling lava. From some of these, lava is seen 



115 



