136 



EARTH FEATURES AND THEIR MEANING 



temperature observations upon the lava in volcanic chimneys, 

 but it seems almost certain that these temperatures rise as the 

 Vulcanian stage is approaching, and such elevation of temperature 

 must be followed by a greater or less re-fusion of the chimney 

 walls. The sequence of events during the late Vesuvian eruption 



FIG. 142. The spine of Pele riding above the chimney of the volcano after 

 the eruption of 1902 (after Hovey). 



is, then, naturally explained by progressive re-fusion and conse- 

 quent weakening of the chimney walls, thus permitting a radial 

 fissure to open near the top and gradually extend downwards. 

 Thus at first small and high outlets were opened insufficient to 

 drain the chimney, but later, on April 7, after this fissure had 



