J. D. Dana — History of the Changes in Kilauea. 27 



fissure between. The block probably slid clown the slope to its 

 bottom ; and, as the talus at the bottom of the lower wall was 

 lifted on the rising floor to make Lyman's ridge, so it appears 

 that this loose block was lifted in the northwest corner ; and 

 the lift along that part of the crater consisted in the restoring 

 of the half engulfed mass with the lava-block on its surface, to 

 its former horizontal position — the position it had when Mr. 

 Brigham's map and observations were made. 



It is interesting to note thus how the 1864-1865 condition of 

 Kilauea grew out of that of 1840, and foreshadowed that of 

 1887. It is worthy of consideration also that just as the fault- 

 plane ah is concentric with the Halema'uma'u basin plus New 

 Lake, so the far greater Kilauea fault-planes, 2000 to 5000 feet 

 north and northeast of the crater (xxxiv, 358), are concentric, 

 not with Kilauea, but with Kilauea plus Kilauea-iki. 



2. DYNAMICAL CONCLUSIONS. 



General cycle of movement in Kilauea. — The history of 

 Kilauea, through all its course since 1823, illustrates the fact 

 that the cycle of movement of the volcano is simply : (1) a 

 rising in level of the liquid lavas and of the bottom of the cra- 

 ter ; (2) a discharge of the accumulated lavas down to some 

 level in the conduit determined by the outbreak ; (3) a down- 

 plunge of more or less of the floor of the region undermined 

 by the discharge. Then follows another cycle : a rising again, 

 commencing at the level of the lavas left in the conduit by the 

 discharge ; which rising continues until the augmenting forces, 

 from one source or another, are sufficient for another outbreak. 



In 1832 the conditions were ready for a discharge when the 

 lavas had risen until they were within 700 or 800 feet of the 

 top ; in 1840, when within 650 feet ; in 1868, when within 500 

 or 600 ; in 1886, when within 350 feet. The greater height of 

 recent time may seem to show that the mountain has become 

 stronger, or better able to resist the augmenting forces. But it 

 also may show a less amount of force at work. In 1823, 1832 

 and 1840, the down-plunge affected a large part of the whole 

 floor of the crater, which proves not only the vastness of the 

 discharges, but also indicates active lava through as large a part 

 of the whole area preceding the discharge, while in 1886, the 

 down-plunge and the active fires in view were confined to 

 Halema'uma'u and its vicinity. It was not in earlier time, 

 therefore, the greater weakness of the mountain, but probably 

 the greater power of the volcanic forces. 



The broad low-angled cone which the volcano tends to make, 

 has a great breadth of stratified lavas to withstand rupturing 

 forces. How great may easily be calculated by comparing a 



