RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 107 



excess of seven miles in circumference. In shape they are irregu- 

 larly elliptical and consist of a series of steps or terraces descend- 

 ing to a pit at the bottom, in which are open lakes of boiling lava. 

 Enough is known of the history of Kilauea to state that the steep 

 cliffs bounding the terraces are fault walls produced by inbreak 

 of a frozen lava surface. The cliff below the so-called " black 

 ledge " was produced by the falling in of the frozen lava surface 

 at the time of the outflow of 1840, the lava issuing upon the 

 eastern flank of the mountain and pouring into the sea near 

 Nanawale. Since that date the floor of the pit below the level 

 of this ledge has been essentially a movable platform of frozen 

 lava of unknown and doubtless variable thickness which has risen 

 and descended like the floor of an elevator car between its guiding 

 ways (Fig. 102). The floor has, however, never been complete, 

 for one or more open lakes are 

 always to be seen, that of Hale- 

 maumau located near the south- 

 western margin having been much 

 the most persistent. Within the 



,'',.,. , . FIG. 102. Schematic diagram to illus- 



open lakes the boiling lava is ap- trate the moving platform of frozen 



parently white hot at the depth lava which rises and falls in the crater 



of but a few inches below the of Kilauea. 

 surface, and in the overturnings of the mass these hotter portions 

 are brought to the surface and appear as white streaks marking 

 the redder surface portions. From time to time the surface 

 freezes over, then cracks open and erupt at favored points along 

 the fissures, sending up jets and fountains of lava, the material of 

 which falls in pasty fragments that build up driblet cones. Small 

 fluid clots are shot out, carrying a threadlike line of lava glass 

 behind them, the well-known " Pele's hair." Sometimes the open 

 lakes build up congealed walls, rising above the general level of 

 the pit, and from their rim the lava spills over in cascades to 

 spread out upon the frozen floor, thus increasing its thickness from 

 above (Fig. 103). At other times a great dome of lava has been 

 pushed up from the pit of Halemaumau under a frozen shell, the 

 molten lava shining red through cracks in its surface and exuding 

 so as to heal each widely opened fissure as it forms. 



At intervals of from a few years to nine or ten years the crater 

 has been periodically drained, at which times the moving plat- 



