Gravity Survey of Lanai— K rivoy and LANE 
347 
PARKING LOT 
QUONSET BUILDING 
LANAI AIRPORT OFFICE 
BAGGAGE AND WAITING ROOM 
AIRPORT BASE IN GRASSED-IN CORNER 
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£ — MACADAM RUNWAY 
SKETCH COPIED FROM Moc DONALD NOTES- 1961 
LANAI AIRPORT BASE 
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' 1 ONE STEP DOWN TO 
STATION: CENTER OF WALK ? 
PARKING LOT 
AND DRIVEWAY 
LANAI INN -AUXILIARY BASE 
Fig. 1 . Sketch showing locations of two gravity 
base stations on Lanai, Hawaii, used in this prelim- 
inary survey. 
the assumption that bulk density above sea level 
was 2.3 g/cc. Because of the accumulation of 
low density material at the surface, an eleva- 
tion correction factor of 0.0693 mgal/ft was 
used in reducing Lanai data for the map of 
Figure 2. This factor corresponds to a density 
of 2.0 g/cc. 
Use of 2.0 instead of 2.3 for specific gravity 
has the result of enhancing the gravity anomaly 
centered on the Palawai Basin. The 40-60-mgal 
Bouguer anomaly over the assumed center of 
volcanism is a prominent feature of the gravity 
fields of other Hawaiian volcanoes (Kinoshita 
et al., 1963). The 40-mgal anomaly centered on 
the Palawai Basin is the major gravity feature 
on Lanai. The geological interpretation of 
Stearns (1940) suggests that the Lanai plateau 
and its contemporary depressions are the re- 
mains of the ancient center of volcanism for 
Lanai Volcano. The gravity interpretation tends, 
therefore, to confirm the geologic one. 
IMPLICATIONS OF THE 
LANAI BOUGUER ANOMALY 
Figure 2 shows the well-defined Palawai 
anomaly. The gravity ridge to the northwest 
indicates the possibility of an ancient rift in 
that direction. There is less control to the south- 
east where another rift zone could possibly 
exist. From R-10 and R-4 one gets a wonder- 
ful view of the scenery; but these stations are 
poor from the point of view of near-station 
elevation change. Whereas other stations along 
the beach or on the plateau get terrain correc- 
tions of less than 1 mgal, computed terrain 
corrections for stations on the mountain go 
from 5 to 15. And in some cases they would 
be even higher were the terrain variations fully 
known and accounted for. Thus R-4 and R-10, 
as plotted, represent idealized Bouguer anoma- 
lies which contain very liberal terrain correc- 
tions. Stations along the eastern shore of Lanai 
would be especially useful in delineating any 
east-west gravity trend not clarified by the pres- 
ent coverage. Such additional coverage is sug- 
gested, as well as possible additions on and 
around the northwest lobe of Lanai. 
ACKNOWLEDGMENTS 
We are grateful to William Aldrich, Dole 
Plantation Manager, for permission to use Doles 
rain gauge data and field maps. Adolph H. 
Desha, Dole Field Superintendent, was most 
generous with his time, advice, and engineer- 
ing data. He has since been kind enough to 
TABLE 1 
Readings at Lanai Inn, 
Corrected Only for Tidal Effect 
DATE 
TIME 
READING 
(mgal) 
12 - 27-62 
13:16 
2472.43 
12-27 
16:11 
2742.49 
12-27 
18:18 
2472.53 
12-28 
07:40 
2472.55 
12-28 
18:10 
2472.58 
12-29 
08:30 
2472.64 
12-29 
11:58 
2472.48 
12 - 29-62 
13:25 
2472.54 
