MOHOKEA CALDERA OX HAWAII / 



western sides the slope is gradual and continuous to the sealevel. On the south- 

 east side tlie lower part of the slope seems to have been interrupted by fractures 

 and the subsidence of large segments of the crust. 



These and other characteristics are shown finely upon the recent (1901) map of 

 Hawaii on the scale of 1 inch equals 10.000 feet, and executed under the direction 

 of AV. D. Alexander."* 



The southerly sides of the Mauna Loa dome have been fractured somewhat dif- 

 ferently from those on the northeast, as evidenced by the eruptions of 186S and 

 1887, as compared with those of 1843, 1855, 1880-81, and 1899. The discharge of 

 lava was rapid through long rents, preceded by vigorous earthquakes in the former. 

 In the latter the discharge has been effected through comparatively small orifices— 

 sometimes gushing forth in fountains, sometimes flowing slowly for months down 

 the mountain's side. 



As is well known, the term "caldera'' was applied by Captain C. E. Button to 

 the three great pit-craters of the territory of Hawaii — Mokuaweoweo, Kilauea, and 

 Haleakala. Each one is an immense depression, ''formed by the dropping of a 

 block of the mountain crust which once covered a reservoir of lava." Within the 

 pit there may be true craters, consisting of lapilli that have been subsequently 

 ejected from beneath. 



Now in Kau, on the southeast side of Mauna Loa, there have been great dis- 

 turbances, giving rise to precipices and blocks of basalt of mountainous dimen- 

 sions, some of which may have been depressed and others elevated, the whole 

 group resembling the buttes of the region of the Cordilleras, with which they were 

 compared by Captain Button. In 1895 J. S. Emerson, of Honolulu, read a paper, 

 "Some characteristics of Kau,"' before the Social Science Association, which will 

 be published in the American Journal of Science. In this he argues the former 

 presence of vigorous volcanic action among these hills back of Hilea ; and, among 

 other things, he suggests the possible derivation of the abundant volcanic ashes 

 from some ancient vent in the Hilea-Mohokea region, rather than from Mokua- 

 weoweo or Keokeo. It was from Mr Emerson that I first learned of the existence 

 of these singular mountains, but it was not until the new map of Hawaii was in- 

 spected that the configuration suggested the presence of an immense caldera at 

 the base of Mauna Loa. Perceiving that the largest area of the depression had 

 the name of Mohokea, I proposed to apply that name to the caldera. This paper 

 was entered for the Rochester meeting, but was then read only by title. 



The Mohokea caldera is a depression carved out of the southern slope of Mauna 

 Loa, embracing an area of exceeding 30 square miles, largelj' occupied for the 

 cultivation of the sugar cane. The longest diameter is 7 miles and the width is 5 

 miles. It diffei*s from Kilauea in that one side has been broken down, and it 

 contains several islands or blocks, mostly depressed below the adjoining slope. 

 Kaiholena is higher than the slope behind it. The inclination from the highest 

 back wall to the front base amounts to 4,500 feet. The base in front may be placed 

 at 1,200 feet ; that behind at 4,000 feet ; and three-fourths of the border has a wall 

 500 feet high. The mountainous blocks are mostly in two parallel lines, though 

 it is likely that a careful survey would exhibit irregularities. The name of the 

 outermost block of the eastern line is Puu Enuhe. Behind it runs into Kulua or 

 Pukulua, the whole range being 4 miles long. Makanao lies in the opening of the 



* A photographic copy was shown at the time of the presentation of this paper. 



