56 THE FLOOR OF THE OCEAN 



therefore needs checking by adequate sounding of the adjacent 

 sea floor; for it is probable that the foundered debris must have 

 contours unlike those normal to the submarine slopes of a 

 basaltic mountain. 



Origin of the Volcanic Heat. — The visible volcanic island, 

 no matter how high, is but the attic story of a building with 

 vastly greater bulk. About this building as well as about its 

 dry-land fraction, we ask two fundamental questions: what is 

 the source of the volcanic heat ? ; and where does the lava itself 

 originate ? In turn the two questions are to be briefly discussed. 



The most accurate measurements of temperature for the 

 live lava in the islands have been made at Kilauea of Hawaii. 

 Figure 28 shows the lake of highly fluent lava, which on a 

 night of 1934 occupied this famous vent. Over most of the lake 

 a thin, opaque film of glass had been developed because of the 

 tremendously rapid radiation of heat to the sky, but near the 

 shore cliff of the lake the boiling liquid burst its way in high, 

 ever-changing fountains. On the left side of the photograph 

 the gas-charged liquid rock cascades from a wall fissure 400 feet 

 above the lake level. 



A few volcanologists attribute the high temperature chiefly 

 to heat-producing, chemical reactions among the primitive 

 gases originally dissolved in the liquid rock. When this com- 

 posite mass is forced up to levels of low pressure, the gases are 

 not in chemical equilibrium; they make new combinations and 

 this with the evolution of heat. Here, then, we have a true 

 furnace-effect, which is most intense at or near the surface. Yet 

 this kind of "combustion" supplies only a partial solution to 

 the heat problem. Still remaining is the fundamental question 

 as to the temperature of the primitive gas before it began to rise 

 from the depths. During the ascent to levels of lower pressure 

 the gas must expand and thereby tend to grow cooler. As yet 

 no way has been found to calculate the amount by which the 



