112 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Mauna Loa lava uplifted by a geologically recent intrusion of magma 

 which is still fluid. The form of the arch suggests a laccolithic body. 

 Though there is, perhaps, no possibility of proving it, this hypothesis 

 has high value in giving a new explanation for the general indepen- 

 dence in the activity of Mokuaweoweo and Halemaumau. The feed- 

 ing channels of a typical laccolith are always narrow. They must 

 freeze quickly and the satellitic injection loses hydrostatic connection 

 with its parent abyssal injection. The latter may most simply be re- 

 garded as that underlying Mokuaweoweo now and during the building 



:> ^ 



MAUNA LOA "^ "o 



- 'S 



•Seo /et^e/ 



(C 



Figure 13. Diagrammatic section to illustrate the hypothesis that the 

 Kilauean vent is fed from a large, still partly fluid laccolith injected into the 

 side of Mauna Loa. The broken line represents the now sealed channel through 

 which the laccolithic magma was injected; its course merely conjectural. 

 Natural scale. 



of most or all of the island of Hawaii. In other words, the postulated 

 laccolith is an offshoot from the main Pacific fissure which located the 

 Hawaiian archipelago. (Figure 13.) 



The remaining evidences favoring this hypothesis may be briefly 

 listed. 



1. The many pit-craters in the eastern Kau district and in the Puna 

 district, including Kilauea, Kilauea Iki, Keanakakoi, Mokaopuohi, etc., 

 are almost unique features in the whole island. (Plate IV, A.) Some 

 of the pits on Hualalai are of similar form and their mode of origin 

 may possibly be connected with another satellitic injection beneath 

 that western cone. The pit-craters of Kau and Puna are not arranged 

 in lines, as if located on master fissures, but are irregularly grouped 

 in clusters. The field evidences show that most, perhaps all, of them 

 have not been opened by explosion, and also that most of them have 

 not emitted lava. The extinct ones, like the active Halemaumau, 

 have been kept open by fusing gases. Their lives have been brief, 

 because dependent upon temporary concentration of juvenile gases 

 at the various points. In origin they are analogous to the clustered 

 blow-holes on the crust of the Kilauean lake between 1820 and 1840. 



2. The Kilauean records show that, from 1820 to 1911, that crater 



