RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 111 



far below the crater, gigantic lava fountains arise at the point of 

 outflow, the fluid rock shooting up to heights which range from 

 250 to 600 or more feet above the surface. A certain proportion 

 of this fluid lava is sufficiently cooled to consolidate while travel- 

 ing in the air, and falling, it builds up a cinder cone which is left 

 as a location monument for the place of discharge. From this 

 outlet the molten lava begins its journey down the slope of the 

 mountain, and quickly freezes over to produce a tunnel, beneath 

 the roof of which the fluid lava flows with comparatively slow 

 further loss of heat. Save for occasional steam jets issuing from 

 its surface, it may give little indication of its presence until it has 

 reached the sea (Fig. 105). 



If sufficient in volume and the shore be not too distant, the 

 stream of lava arrives at the sea, where, discharging from the 



FIG. 106. Lava stream discharging into the sea from beneath the frozen roof of 

 a lava tunnel. Eruption of Matavanu on Savaii in 1906 (after Sapper). 



mouth of its tunnel, it throws up vast volumes of steam and in- 

 duces ebullition of the water over a wide area (Fig. 106). Pro- 

 fessor Dana, who visited Hawaii a few months only after the 

 great outflow of 1840, states that the lava, upon reaching the 



