A Gravity Survey of the Island of Hawaii 1 
W. T. Kinoshita 
A BOUGUER ANOMALY CONTOUR MAP, based 
on a gravity survey made on the island of Ha- 
waii during parts of 1961 and 1962 (Kinoshita 
et al., 1963), is presented as Figure 1. The 
table of principal facts is reported elsewhere 
(Hawaii Inst. Geoph., 1965, Table 1). Meas- 
urements along the main roads and trails pro- 
vided generally good coverage at elevations 
below 6000 ft, but at higher elevations large 
areas are inaccessible, and the gravity map is 
necessarily generalized. 
About two-thirds of the stations were located 
at bench marks or spot elevations published on 
standard 1:24,000 scale U. S. Geological Sur- 
vey topographic quadrangle maps. The rest 
were located at similar points on 1:62,500 
scale maps. All of the gravity measurements 
were made with a LaCoste Romberg gravi- 
meter relative to a base station at the Ha- 
waiian Volcano Observatory, which has an 
observed gravity value of 978,664.42 mgal. 
Topographic and Bouguer corrections were 
made in the same manner as those on Maui 
(Kinoshita and Okamura, pp. 000 in this 
issue) with the exception that topographic 
corrections were made at about 50% of the 
stations instead of at 15% as on Maui. In the 
table the complete Bouguer anomaly is given 
to 0.1 mgal at those stations where the topo- 
graphic correction was calculated, and to the 
even mgal where they were estimated. 
The gravimeter was read at the base station 
several times during the course of approxi- 
mately 30 days of field work and the maximum 
variation in the readings was 0.7 mgal. Correc- 
tions for instrumental drift and tidal effects 
1 Publication authorized by the Director, U. S. Geo- 
logical Survey. 
were neglected in the calculations; their com- 
bined effects could be as large as 1 mgal. Al- 
though the maximum variation in base read- 
ings was as much as 0.7 mgal, about 90% of 
the readings were within 0.2 mgal. Thus, any 
one observed gravity value could be in error 
by as much as 1 mgal, but is probably correct 
to within 0.5 mgal. Most of the published ele- 
vations are accurate to within 5 ft of their true 
elevations, but for the parts of the island where 
only the smaller scale topographic maps were 
available, the elevations could be in error by 
15 ft. In terms of a combined free-air Bouguer 
correction, these elevation uncertainties would 
correspond to errors of about 0.3 mgal and 1 
mgal, respectively. Topographic corrections are 
probably correct to within 10%. Hence the 
largest topographic corrections, such as the 50- 
to 60-mgal values obtained at the summits of 
Mauna Loa and Mauna Kea, can introduce 
errors up to 6 mgal. However, most of the sta- 
tions had topographic corrections of less than 
20 mgal, so the complete Bouguer anomaly 
value at any one station is probably accurate 
to at least 3 mgal. 
REFERENCES 
Hawaii Institute of Geophysics. 1965. 
Data from gravity surveys over the Hawaiian 
Archipelago and other Pacific Islands. Hawaii 
Inst. Geoph. Rept. 65-4, March 1965. 10 
tables. 
Kinoshita, W. T., H. L. Krivoy, D. R. 
Mabey, and R. R. MacDonald. 1963. Grav- 
ity survey of the island of Hawaii. In: Short 
papers in the geological sciences. U. S. Geol. 
Survey Prof. Paper 47 5-C: Cl 14-C1 16. 
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