SPACING OF VOLCANOES 507 



jecture, but is of interest in the above problem in its relation to the 

 growth of the volcanoes progressively or irregularly along the major rift 

 which underlies the islands. The volcanoes which built the original 

 doublet Kauai were apparently contemporaneous. Western Oahu was 

 carved almost to its present form before eastern Oahu robbed it of the 

 moisture from the trade winds. Mauna Loa., on western Molokai, may 

 have appeared before eastern Oahu, and the latter is of approximately 

 the same age as eastern Molokai. Kohala and West Maui were probably 

 contemporaneous and both may have become extinct before Haleakala, 

 Hualalai, and Mauna Loa appeared. Ilualalai and Plaleakala ceased 

 activity in historic time long after Mauna Kea became extinct, but both 

 Hualalai and Kilauea were active before Mauna Kea ceased to grow and 

 before the sea-cliff from Hilo to Kukuihale was cut to its present depth. 



While the spacing of the major vents suggests a progression of activity 

 through each volcano in turn, the evidence observable on the summits of 

 the volcanic piles, as just indicated, does not substantiate this suggestion. 



Kilauea is here considered to be an independent volcano and older 

 than its more lofty neighbor for the reasons given below. This conclu- 

 sion does not prevent a sympathy in the activity of these volcanoes, as the 

 evidence at hand favors sympathetic action, often very marked, but occa- 

 sionally not especially noticed by observers in the past. 



(1) The Kilauean sink is surrounded by pahoehoe flows, which may 

 be seen in cross-section in the numerous fissures and faults found on all 

 sides of the sink, and which may be studied in the Kau desert beyond the 

 ash. The flows outside the sink are from one to three feet in thickness, 

 like those within the sink, and the individual flows and festoons in the 

 lava radiate from Kilauea, not Mauna Loa. The Mauna Loa flows, which 

 have been pouring down the slopes of that mountain toward Kilauea, are 

 largely thick, rough aa flows. 



(2) The walls of Kilauea show thick and thin ash sections^^; thin 

 lava flows of very local extent, such as would not be expected in flows 

 from the lofty slopes of Mauna Loa, and at least one unconformity,^* due 

 either to faulting or to erosion before the slopes of Mauna Loa diverted 

 the rainfall from the summit of Kilauea east of the Volcano House. 



(3) As seen from the vicinity of Punaluu and Honuapo, in Kau, the 

 form of Kilauea clearly resembles that of the summit of Mauna Loa from 

 a like distance. 



(4) The signs of old age in Kilauea, with ash. cones and pit craters on 

 the Kau desert and on the eastern flank of the mountain toward Kapoho, 



13 S. Powers : Explosive ejectamenta of Kilauea. Am, Jour. Sci., vol. 41, 1916, pp. 

 227-244. 



"Idem, p. 230. 



