A Gravity Survey of the Island of Niihau, Hawaii 1 
Harold L. Krivoy 2 
ABSTRACT: Gravity data collected on Niihau support geologic evidence that the 
island is an erosional remnant of a dead shield volcano whose center of volcanism 
was just east of the present Niihau highlands. Bathymetric and gravity evidence 
offer clues to a genetic link between Niihau and west Kauai; onshore gravity sug- 
gests a continuous Bouguer high connecting the two regions. This link would be 
in accord with ocean-bottom topography, which shows a prominent ridge rising 
above sea level at Niihau and at Kaula Rock to the west. 
A GRAVITY SURVEY of the island of Niihau, 
Hawaii, was made December 10-12, 1963. It 
is a pleasure to acknowledge the logistic sup- 
port, the check of place names, and the hospi- 
tality of Aylmer Robinson, Manager, Niihau 
Ranch. Without his interest this work would 
not have been possible. I am indebted also to 
Niihau residents Melvin Pahulehua, Gilbert 
Pahulehua, Jr., Jacob Kanahele, and Keoki Kea- 
moai, who helped me reach the station sites 
on Niihau. 
Stations were selected by use of the existing 
1929 U. S. Geological Survey topographic sheet 
to determine their elevations. Because of the 
somewhat generalized character of this map, 
elevations at many stations may be in error by 
as much as 20 ft. Such an error in elevation 
would lead to an error of about 1.4 mgal in 
the Bouguer anomaly, if we assume a density 
of 2.3 g/cm 3 for island rocks down to sea level. 
This basic uncertainty of exact elevation made 
it superfluous to consider other, much smaller, 
variables. Thus, I did not make corrections for 
tidal gravity changes or for meter drift. The 
latter correction, however, would have been 
especially small because of the accuracy of the 
LaCoste and Romberg low-drift portable grav- 
ity meter used in this survey. The table of 
principal facts is reported elsewhere (Hawaii 
Inst. Geoph., 1965, Table 8). 
Despite its rather small land area Niihau ex- 
hibits a large positive Bouguer anomaly similar 
to those anomalies found on other Hawaiian 
1 Publication authorized by the Director, U. S. Geo- 
logical Survey. 
2 U. S. Geological Survey, Denver, Colorado. 
volcanoes. A linear high, outlined by the 280- 
mgal contour, crosses Niihau in a direction N 
70° E (Fig. 1) approximately parallel to the 
submarine ridge which joins Niihau, Kauai, 
and Kaula (Stearns, 1947: Fig. 3). A 280- 
mgal high also enters Kauai (Krivoy et al. 
p. 354 in this issue) from the direction of 
Niihau, but no gravity data are available over 
the submarine ridge between Kauai and Niihau. 
Geologic mapping indicates that Niihau is 
a remnant of an ancient volcanic shield which 
had its center offshore east of the highlands 
(Stearns, 1947; Macdonald, 1947). The gravity 
map (Fig. 1) supports this interpretation. 
Comparison of the gravity field of Niihau with 
the fields of other, less dissected Hawaiian vol- 
canoes (Kinoshita et al., 1963) suggests that 
the original volcanic center of the Niihau vol- 
cano is close to its eastern shore. Kilauea and 
Mauna Loa have their centers of volcanism 
within 10 miles of the 280-mgal contour on 
their flanks or rifts. An offshore gravity survey 
between Kauai and Niihau would be of inter- 
est because it might delineate the central por- 
tion of the original Niihau volcano and clarify 
the relation between Niihau and west Kauai. 
The N 70° E trend of the Kaula-Niihau- 
west Kauai ridge (Stearns, 1946: PI. 1) is per- 
pendicular to the northwest trend of the main 
Hawaiian ridge. Recent bathymetric surveys 
(U. S. Navy Hydrographic Office, 1961) have 
detailed a system of topographic lineaments 
which give the appearance of having been 
parted by the growing Hawaiian ridge. These 
lineaments trend N 70° E to N 80° E, about 
parallel to the Kaula-Niihau-west Kauai ridge. 
359 
