514 S. POWERS TECTONIC LINES IN THE HAWAIIAN ISLANDS 



point near Kolekole Pass. Likewise, lava flows surrounding lao Valley 

 and Kilohana crater (Kauai) do not dip away from these areas, which are 

 frequently called calderas and compared with the Lualualei basin. 



Kauai was originally composed of two volcanoes, as stated above. Dana, 

 in his first visit to the islands, was the first to notice that the flows trun- 

 cated in the Napali cliffs (plate 33) dip toward Waialeale; but he sup- 

 posed that Mihau represented the missing volcano, moved southward. 



Niihau is so carefully protected from visitation by its owner that little 

 is known concerning this desert island. The northeastern portion is 

 bounded by a fault-scarp, along which the greater part of the original 

 island has subsided; but this scarp is not a continuation of that at Napali. 



Summary 



An examination of the hypotheses which have been proposed to account 

 for the spacing of the volcanoes of the Hawaiian Islands has shown that 

 the most plausible is based on a series of fracture lines which are part of 

 a major fracture system. A remarkably uniform spacing of the vents 

 has led to the suggestion that they have arisen in an orderly manner along 

 two sets of fractures which comprise this system. The explanation of a 

 rather definite arrangement of vents in purely volcanic islands in contrast 

 to the frequent lack of arrangement in continental islands and on conti- 

 nents lies in the fact that the former have arisen from the deep-sea floor 

 instead of having broken through groups of resistant rocks. 



Along the Hawaiian rift the volcanoes have arisen not in exact order 

 from west to east, but in a somewhat irregular manner, with a general 

 migration of the lava in an easterly direction. Furthermore, the order 

 of extinction of volcanic activity has not always been the same as the 

 order of initiation. Evidence is presented to show that Mauna Loa is 

 younger than Kilauea. 



No connection has been found to exist between the lines of fracture 

 now apparent in the islands with any other tectonic lines. While the 

 growth of the volcanoes is dependent on the major fracture system and 

 while there may be a sympathy of action between volcanoes during growth, 

 the breakdown of each volcanic mass appears to be independent of that 

 of any other mass. Normal faulting with the development of graben has 

 been shown to offer an explanation for the structural features described. 



