508 S. POWERS TECTONIC LINES IN THE HAWAIIAN ISLANDS 



are more evident than those of the higher mountain. The pit craters 

 can be duplicated on Hualalai, but the alignment along the course of the 

 1840 outbreak is lacking in the pits on the summit of Hualalai. 



(5) Normal faults^ as described below, bound the south shore of 

 Kilauea and rift lines diverge from the summit of the mountain, showing 

 the further breakdown of the old volcano. 



ISToRMAL Faulting 



Lines of weakness may be observed on almost all the islands of the 

 group as features quite distinct from the M^ave-cut cliffs or from con- 

 traction cracks in lava flows or from the escarpments formed by the abrupt 

 foot of a large aa flow. Commencing with Kilauea, the major structural 

 lines may be described as they occur on each island. 



Halemaumau, the summit sink of Kilauea, appears to have a direct 

 connection with certain lines of weakness^^ which radiate from it: one 

 extending down the Kau desert to the sea east of Pahala, and from which 

 the flows of 1823 and 1868 issued (plate 29, figure 1) ; another extending 

 from the prisoner's quarry north of the Volcano House toward Olaa ; and 

 probably a third extending from Keanakakoi and the Twin Craters past 

 Puu Huluhulu, Makaopuhi, Heiheialiulu, and in the direction of the 

 1840 flows and of the Kapoho craters. Along these lines true rifts may 

 be seen near the Kilauean sink, and in the case of the first line open 

 fissures and faults formed in part in 1823 and 1868, but principally in 

 prehistoric time, may be followed from Halemaumau to the sea. In 

 1868 a small graben or large fissure 30 feet in width and 40 feet in depth 

 was opened from near the Kapapala ranch house to the sea and the pahoe- 

 hoe flow issued from the head of the rift concomitantly with its forma- 

 tion. As the pahoehoe flowed toward the sea, on both sides of tlie open- 

 ing, small rivulets flowed into the fissure, as shown in plate 29, figure 2. 



A breakdown of Kilauea, previously mentioned by Hitchcock,^*^ is found 

 in the Keauhou pali, a series of cliffs south of the line of pit-craters and 

 extending from Kalapana to the flow of 1823, a distance of 27 miles. 

 On the west these cliffs, produced by normal faulting, are covered by the 

 great number of flows which have poured down the southwest flank of 

 the mountain from far back into historic time until 1868. Near the cen- 

 ter of the faulted area, on the trail from the Volcano House to the Keau- 

 hou landing, a number of fault-scarps are traversed. These cliffs, over 



i"> First pointed out to tlie writer by Prof. T. A. Jaggar, Jr., and by Mr. H. O. Wood ; 

 described in part by C. H. Hitchcock, Hawaii and its volcanoes, HonoluUi, 1911, pp. 

 108-109 ; Bull. Seis. Soc. Am., vol. 2, 1912, p. 190, and by H. O. Wood, Bull. Seis. Soc. 

 Am., vol. 4. 1914, pp. 169-203. 



18 The Hawaiian earthquake of 1868. Bull. Seis. Soc. Am., vol. 2, 1912, pp. 188-189. 



