506 S. POWERS TECTONIC LINES IN THE HAWAIIAN ISLANDS 



The average distance between these vents is 25.6 miles, the maximum 

 about 35 miles and the minimum about 19 miles. The Waialeale center 

 of Kauai is 100 miles from the Waianae center of western Oahu, the 

 Koolau center of eastern Oahu is 44 miles from Mauna Loa (western 

 Molokai), and the Kohala center is 52 miles from Haleakala. Dividing 

 these distances into four, two, and two units respectively, the average unit 

 is 24.5 miles, as if the spaces betM^een the islands had the same significance 

 as the spaces between the centers of activity now visible above sealevel. 



It was the regular arrangement above tabulated which led W. L. Green 

 to his hypothesis of the triangular network of lines with the centers of 

 activity at the intersections of these lines ; and, while the actual arrange- 

 ment does not fit Green's scheme, there appears to be an underlying cause 

 for the arrangement. Two parallel lines can be drawn along the axis of 

 the islands which will fall near the centers of activity, and these lines 

 may be intersected by a set of lines transverse to their axis which will fall 

 on these centers and which, by curving, may be made to fall along the 

 rift lines visible on the flanks of Mauna Loa and Kilauea. 



A theory explaining the origin of the volcanoes along intersecting 

 curved lines is supported by the field evidence of a row of cones on the 

 flank of Kohala pointing toward Haleakala and of a row of cones on 

 Haleakala pointing toward Kahoolawe and almost connecting these two 

 volcanoes above sealevel. On the contrary, the lines of weakness now 

 seen may have no connection with those beneath the volcanic piles. The 

 breakdown of the volcanoes has no connection with either the island align- 

 ment or with any hypothetical cross-lines. 



The most satisfactory theory yet advanced for the alignment of the 

 vents appears to be that based on a major fracture system in the earth's 

 crust, the principal volcanoes arising at about equal distances of 25 miles, 

 but not necessarily in successive order or at every point. The superficial 

 fracture system has its major trend following the direction of the island 

 chain on which are superimposed the secondary, divergent fractures 

 arranged en echelon. That there are some deeper-seated lines of weak- 

 ness on which the above system is superimposed appears probable, judging 

 by the morphology of the arcuate groups of islands fringing the Asiatic 

 continent and the more or less lineal chains of islands in Oceania.^^ 



Two factors with regard to the relative age of volcanoes must be con- 

 sidered — the time of their beginning and the time of their extinction. 

 The order of beginning, which may be judged only by the small summits 

 of this range of lofty peaks projecting above sealevel, is a matter of con- 



12 Prof. B. Koto has recently suggested that the "festoon islands" of Japan owe their 

 origin and form to a major fracture system. Morphological summary of Japan and 

 Korea, Jour. Geol. Soc. Tokyo, vol. 23, 1916, p. 172 (34). 



