232 S. Powers — Explosive Ejectamenta of Kilauea. 



The age of the ejectamenta is very difficult to determine, 

 even with reference to the very recent geological history of 

 Kilauea, on account of the very meager descriptions of the early 

 visitors, [n 1823 Ellis saw "large stones and volcanic rocks" 

 of the 1789 eruption on the floor of the sink now covered with 

 lava.* The only material which has been ejected from Kilauea 

 over the surrounding region since the eruption of 1789 is Pele's 

 hair, which is frequently seen in large quantities on the Kau 

 desert. The largest part of the ash must be of pre-historic age 

 because it is overlain by the pre-historic Keamoku flow from 

 Mauna Loa, is greatly altered in places where the steam-vents 

 of past ages have been active, and is faulted in the fissures and 

 faults seen especially on the south side of the sink, as will be 

 shown below. 



The origin of the ash has been discussed by Dana, Hitch- 

 cock, J. S. Emerson, Perret, and others. A number of 

 measurements made by the writer in 1915 may serve as a basis 

 for the presentation of the subject in a more complete manner 

 than before. Heretofore the entire surficial deposit has been 

 considered as the material of the 1789 eruption. It is shown 

 below that this is probably not the case, and that there have 

 been at least two ash eruptions since the last flow of lava 

 spilled over the edge of the original Kilauea crater on to the 

 region surrounding the present sink.f 



On the northeast side of Kilauea, from the Halfway House 

 past Kilauea Iki as far as Keanakakoi, the sections show 

 thread-lace scoria at the base overlain by yellow ash with a 

 stratum of fragments of basalt, scoria, and coarse ash. On the 

 southwest side, the basal thread-lace scoria is missing and in 

 its place is found yellow ash, with occasional thin layers of 

 black sand with many olivine crystals, and of thread-lace scoria, 

 overlain by coarse ejectamenta. On the surface near the sink 

 are many blocks and bombs of large size which have made 

 depressions in the ground where they struck. A thin veneer 

 of the thread-lace scoria is found on the edge of the Kau 

 desert, but the greater part of this light material has blown 

 away since 1825 when seen by Goodrich, and even since 1864, 

 when Dr. W. T. Brigham made his first survey of Kilauea. 



The basal thread-lace scoria northeast of Kilauea rests 

 directly upon the pahoehoe flows and is overlain conformably 

 by ash. The thickness of the thread-lace scoria at places 

 where it can be measured is (see fig. 3) : 6 feet at the edge of 

 one of the fault-blocks just north of the place where the trail 

 from the Yolcano House to Halemaumau meets the floor of 



* C. H. Hitchcock, Hawaii and its Volcanoes, Honolulu, 1911, p. 171. 



fThe writer is indebted to Professor T. A. Jaggar, Jr., for many sugges- 

 tions in the field, and to Professor R. A. Daly for kindly criticism of the 

 manuscript. 



