THE ERUPTION OF VESUVIUS IN APRIL, 1906. 227 



The Strombolian phase increased in intensity from 8 to 10.45 p. ni. 

 The incandescent material was elevated '2 kilometers above the crater. 

 The outbursts succeeded each other so quickly that they seemed con- 

 tinuous and resembled fountains of fire. According to Mercalli, 

 the summit of the mountain was covered with a continuous bed of 

 incandescent material, from which blocks were constanth^ rolling to 

 lower levels. 



At 10.45 p. m., at the moment when the opening of Cognoli became 

 most active, the crater seemed to calm itself for some minutes and 

 tlien suddenly its activity became more furious than ever. At 12.31 

 a. m., and then at 2.40 a. m.. great detonations were heard and earth- 

 quakes were experienced throughout the Vesuvian region. This was 

 tJie maxinnnn stage of the eruption, when the explosions passed 

 from the Strombolian phase to the Vulcanian. The material ejected 

 became less incandescent and finally Avas completely dark. 



At this moment an enormous quantity of lapilli, mixed with 

 blocks, was thrown northeast toward Ottajano. This fall of lapilli 

 caused most of the fatalities of the eruption and destroyed much 

 property. 



The explosive maximum ajiparently coincided with the effusive 

 maximum. 



The ejection of lapilli lasted only a few hours, but at the same time 

 and during the entire day of the 8th and the following days there 

 Avere successive violent Vulcanian explosions, casting their solid 

 materials upon the cone. The thick clouds of material brought dark- 

 ness upon the flanks of the volcano, and the condensation of water 

 vapor caused floods of mud. 



These Vulcanian ejections, at first continuous and violent, gradu- 

 ally diminished in intensity and took place at rarer intervals, until 

 about the middle of May, when they ceased. 



During some days succeeding the paroxysm of the 8th the slopes 

 were constantly enveloiDed in a thick cloud of dust. When it cleared 

 away the form of the summit was seen to have been profoundh' 

 altered by the truncation of the cone, accompanied by a widening 

 and deepening of the crater. This was the source of the enormous 

 amount of material thrown out by the Vulcanian explosions. 



The period of activity has been further characterized by the pro- 

 duction of dry avalanches, by earth movements, and by intense elec- 

 tric phenomena, and it has been followed by torrents of mud and by 

 exhalations. 



The principal phenomena will now be considered in greater detail. 



EFFUSION OF LAVA. 



The flows of basic magma present an entirely different aspect, 

 according to the temperature and velocit}^ with Avhich they are emit- 



