RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 137 



been much extended and a new and larger one had opened at a 

 lower level, the draining began and the surface of lava commenced 

 rapidly to sink. 



When the rapid sinking of the lava surface occurred, the lower 

 lava layers were almost immediately relieved of pressure, thus 

 causing a sudden expansion of the contained steam and resulting 

 in grand crater explosions. The partially re-fused and fissured 

 upper chimney, now unable to withstand the inward pressure of 



FIG. 143. Outlines of the Pel6 spine upon successive dates. The full line repre- 

 sents its outline on December 26, 1902 ; the dotted-dashed line is a profile of 

 January 3, 1902 ; while the dotted line is that of January 9, 1903. The dark 

 line is a fissure( after E. O. Hovey). 



the surrounding tuff walls, since outward pressures no longer 

 existed, crushed in and contributed its materials and those of 

 the surrounding tuff to the fragments of fresh lava rising in 

 volume in the grand explosions (Fig. 141 c). In outline, then, 

 these seem to be the conditions which are indicated by the 

 sequence of observed events in connection with the late Vesuvian 

 outbreak. 



The spine of Pele. The disastrous eruption of Mont Pele 

 upon Martinique in the year 1902 is of importance in connection 

 with the interesting problem of the upward growth of volcanic 

 chimneys during the cone-building period of a volcano. After 

 the conclusion of this great Vulcanian eruption, a spine of lava 



