344 
PACIFIC SCIENCE, Vol. XIX, July 1965 
Offices 
Baggage 
and 
Terminal 
room 
Garages 
Chain link fence 
Apron 
Lamp- 
u posf 
truck | 
drive- 
way I 
FIG. 1. Plan of Molokai airport. X, site of gravity 
station No. 23. 
GRAVITY 
A Bouguer gravity map (Fig. 3) was pre- 
pared for the island from gravity measurements 
from 72 stations. The table of principal facts 
is reported elsewhere (Hawaii Inst. Geoph., 
1965, Table 3). As with gravity surveys of the 
Island of Hawaii (Kinoshita et al., 1963), a 
density of 2.3 g/cc was used for the Bouguer 
corrections. No systematic tidal, drift, or ter- 
rain corrections have been made. 
Like other Hawaiian volcanoes, West Molo- 
kai Volcano shows a well-marked gravity high 
near the center. This anomaly presumably rep- 
resents the higher percentage of denser intrusive 
rocks and perhaps ponded lavas associated with 
the magma reservoir and central conduit of the 
volcano. This anomaly, however, lies consider- 
ably east of the high part of the volcano and, 
in fact, is largely within the area of extensive 
faulting on the northeast flank of the volcano. 
Much of this central positive gravity anomaly 
lies in the area covered by the younger lavas of 
East Molokai Volcano. The relationship of the 
fault system on the northeast flank of West 
Molokai Volcano to the gravity-defined vol- 
canic center suggests that these faults, prob- 
ably caused by gravity sliding to the north, en- 
croached on the volcanic center in much the 
same way as the Hilina fault system is encroach- 
ing on the south flank of Kilauea Volcano 
(Moore and Krivoy, 1964:2043). 
Gravity noses trending northwest and south- 
west from this central gravity high (Fig. 3) 
presumably define the major rift zones of West 
Molokai Volcano. A gravity nose extending to 
the east may represent an east rift zone of the 
west volcano, but in this region of overlap the 
possibility that this structure belongs to East 
Molokai Volcano cannot be eliminated. Control 
of gravity measurements on the south coast of 
West Molokai is insufficient to test the presence 
of a southeast rift zone. 
The gravity measurements on East Molokai 
Volcano are few and are restricted chiefly to the 
south and east coastal region and to the Kalau- 
papa peninsula to the north. No gravity meas- 
urements were made near the mapped caldera 
complex and the character of the central gravity 
configuration is not known. Terrain corrections 
have been computed for four stations on East 
Fig. 2. Geologic sketch map of the island of Molokai. After Stearns and Macdonald (1947) and Stearns 
(1946). 
