RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 127 



vius we find the crescent-like rim of Monte Somma; on Etna it 

 is the Val del Bove, etc. It is this caldera of composite cones 

 which gave rise to the theory of the " elevation crater " of von 

 Buch (see ante, p. 95, and Fig. 127). 



The eruption of Vesuvius in 1906. The volcano Vesuvius 

 rises on the shores of the beautiful bay of Naples only about ten 

 miles distant from the city of Naples. The mountain consists of 

 the remnant of an earlier broad-mouthed explosion crater, the 

 Monte Somma, and an inner, more conical elevation, the Monte 

 Vesuvio. Before the eruption of 1906 this central cone was sharply 

 conical and rose to 

 a height of about 

 4300 feet above 

 the surface of the 

 bay, or above the 

 highest point of the 

 ancient caldera. 

 The base of this 

 inner cone is at an 

 elevation of some- 

 thing less than half 

 that of the entire 

 mass, and is sepa- 

 rated from the en- 

 circling ring wall of the old crater by the atrio, to which corre- 

 sponds in height a perceptible shelf or piano upon the slope toward 

 the bay of Naples (Fig. 128). 



An active composite cone like that of Vesuvius is for the greater 

 part of the time in the Strombolian condition ; that is to say, light 

 crater explosions continue with varying intensity and interval, 

 except when the mountain has been excited to the periodic Vul- 

 canian outbreaks with which its history has been punctuated. 

 The Strombolian explosions have sufficient violence to eject small 

 fragments of hot lava, which, falling about the crater, slowly built 

 up a rather sharp cone. The period of Strombolian activity has, 

 therefore, been called the cone-producing period. Just before each 

 new outbreak of the Vulcanian type, the altitude of the mountain 

 has, therefore, reached a maximum, and since the larger explosive 

 eruptions remove portions of this cone at the same time that 



FIG. 128. View of Mount Vesuvius as it appeared from 

 the Bay of Naples shortly before the eruption of 1906 

 The horn to the left is Monte Somma. 



