510 S. POWERS TECTONIC LINES IN THE HAWAIIAN ISLANDS 



Mauna Loa is a vast mountaiu of basalt which has reached the stage 

 where foniitaining of very liquid lava takes place in the summit sink and 

 flows break out on the sides, principally along two lines of weakness which 

 are approximately parallel to the two best developed Kilauean lines of 

 weakness. These lines are well marked at Mokuaweoweo, according to 

 Dr. T. A. Jaggar, Jr., and the one extending to the south is marked by a 

 fault-scarp extending from Kahuku, near Waiohinu, to the sea at Ka Lae, 

 and attaining a height of from 800 to 1,000 feet near the sea. The dis- 

 placement is down on the west side, and west of the fault the country is 

 a waste of young lava flows, including those of 1907 and 1916. It was 

 near this fault that a lateral shift of 18 feet took place in 1868, along a 

 north-south line, the east side being moved north with respect to the west 

 side. Another north-south fault-scarp is seen east of Waiohinu extend- 

 ing toward Naalehu. Whether the volcano was built up along the two 

 lines of weakness which are now apparent is uncertain, but the elongation 

 of the mountain in one direction is certainly toward Kahuku. 



Elsewhere normal faulting occurred on the sides of Mauna Loa, for 

 Kealakakua Bay is bounded on the north between Kaawaloa and Napoo- 

 poo by a fault-scarp which appears to continue, beneath a thick covering 

 of later flows, south as far as Papa. Abnormal steepness of the mountain 

 slope below the highway from north of Hookena to Papa seems explicable 

 on no other grounds. N"ear Napoopoo a young flow cascades over the 

 fault-scarp, as do flows over the Keauhou pali. At ITonaunau, south of 

 the City of Eefuge, there is a low escarpment, overrun by a young flow, 

 which possibly represents a parallel fault of small magnitude. 



Mohokea, an amphitheatral depression in the side of Mauna Loa above 

 Hilea and Pahala, has been described as a crater (or sink) comparable to 

 tlie Kilauean sink.-- It is 6 miles long from northeast to southw^est 

 and 5 miles wide. The depression is younger tlian the surrouiRling flank 

 of Mauna Loa because the flows of tliat mountain are truncated in the 

 walls of Mohokea. The floor of Mohokea slopes seaward and on the 

 northeast side is underlain by alternating lava flows and ash beds.--' 

 Kaumaikeohn is a pointed hill rising at the entrance to Mohokea on the 

 northeast;^* Puu Iki rises on the northwest part of the rim, and Kaiho- 

 lena, Pakua, and Makanao rise on the southwest. In the center is a row 

 of conical and of flat-topped hills extending from Puu Enuhe toward 

 Puu Iki, Near the entrance to the depression a number of flows have 



22 c. H. Hitchcock : Hawaii and its volcanoes, Honolulu, 1911, pp. 149-153. 



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

 242-243. 



2* An ascent of this hill, with the aid of a cane knife, revealed no rock exposures, but 

 showed a fissure 6 feet deep crossing the northwest rim. 



