S. Powers — Explosive Ejectamenta of Kilauea. 239 



outside the pit-craters Kilauea Iki and Keanakakoi ; and the 

 fault-blocks inside the sink which have not been buried by 

 lava flows from the various Kilanean lakes of former times. 

 The bedding planes of this explosive material are always 

 parallel to the upper surface of the lava-flows upon which they 

 rest, no matter at what angle the fault-blocks are tilted. More- 

 over, the faults which bound these blocks truncate the partly 

 consolidated ash beds as well as the underlying lava flows, and 

 the fault-scarps in the ash are almost perpendicular. If the 

 faulting had taken place before the fall of the ash, the latter 

 should have accumulated to a greater thickness on the lower 

 side of a block tilted at an angle of 10° than on the upper side 

 unless the ash fell when the trade winds were not blowing. 

 Moreover, ash deposits 5 to 10 feet in thickness would have 

 smoothed off the topography and filled small fissures; and 

 even in the case of a fault such as bounds the "Peninsula" 

 on the south, where there is a cliff of ash and ejectamenta 36 

 feet in thickness standing in an almost perpendicular wall, the 

 ash could scarcely have fallen on the edge of a preexisting 

 cliff of truncated lava-flows and not have reached an angle of 

 repose of about 30°. It may be argued that the faults 

 referred to are not a part of the series of major collapses by 

 which the sink has gradually been formed ; but the same story 

 is told in the blocks in front of the Volcano House, at Uweka- 

 huna, at the monocline southwest of the crater, and in the 

 rifts from Keanakakoi westward. Surely almost all of these 

 faults were seen by Ellis in 1823 and they must have been 

 formed before 1789 and during the collapse of the sink. 



The formation of a sink the size of those at Kilauea and at 

 the summit of Mauna Loa (Mokuaweoweo) must be a very 

 slow break-down, judging from the changes which have gone 

 on in these sinks from the time of the earliest records up to 

 the present, by a mechanism not well understood. Even if the 

 Kilanean sink took a very long time to form, and if the ash 

 eruptions took place early in the process, these porous beds of 

 ash would not show their great age because they do not retain 

 water and therefore suffer extensive alteration only by steam. 



One more question presents itself if the arguments above be 

 accepted. From what source did the ash come : was the sum- 

 mit of Kilauea pitted by a few craters similar to those on 

 Hualalai or Mauna Kea which have thrown out extensive ash 

 deposits, or was there just a summit crater which suddenly 

 became explosive? As there is no evidence that there ever 

 were any ash cones of any magnitude on the summit of 

 Kilauea, the flrst suggestion is unlikely. If there was a crater 

 of the Halemaumau type on the summit, there may have been 

 a situation somewhat resembling 1789, when, after a long 



