Gravity Survey of Kauai- — Krivoy, Baker, and Moe 
357 
stations on the rather steep Mauna Kea The 
gravity configuration over the low shield vol- 
cano Kilauea, however, was only slightly modi- 
fied by consideration of terrain both on land 
and off-shore. The more subtle gravity anoma- 
lies, such as those on Mauna Kea and Mauna 
Loa, were "improved” by the addition of ter- 
rain correction, albeit this was in a direction 
which emphasized correlation between gravity 
and topography. Strong gravity features, such 
as the Kohaia and Kilauea anomalies, were in- 
creased in size and gradient but were not seri- 
ously displaced in the final terrain-corrected 
product. On Hawaii, for example, stations at 
the Bouguer high on Kohaia volcano received 
less than 6 mgal of terrain correction. Stations 
on Kilauea received less than 5 mgal. The major 
Kauai Bouguer anomaly, in this same sense, 
would be augmented but not seriously shifted. 
Figure 2 shows the location of gravity sta- 
tions and the Bouguer value for each on the 
island of Kauai. It also shows the location of 
the Olokele caldera mapped by Stearns (1946) 
and by Macdonald et al. (I960). Macdonald 
et al (1960:32-33) state that "the major cal- 
dera of the Kauai shield” is "twice the size of 
Mokuaweoweo on Mauna Loa . . . but its 
boundaries are not accurately known.” The 
Bouguer high, as mapped and contoured on 
Figure 2, does not coincide with the caldera 
inferred from geologic data. The 340-mgal high 
is centered about 10 miles east of the center of 
Olokele caldera. If the relations are similar to 
those of the other Hawaiian volcanoes studied, 
the gravity high outlines the most persistent 
source of lava responsible for building the Kauai 
shield and probably the caldera site, but the 
exact relationship between Bouguer high, topo- 
graphic high, and mapped caldera complex re- 
quires further study. 
The absence of a gravity nose extending from 
the gravity high, such as that along the east rift 
zone of Kilauea, is in agreement with the ab- 
sence of any marked submarine ridge radiating 
outward from the island in that direction. 
A second anomaly on Kauai is the west- 
trending high which emerges on the west side 
of the island. Mapping by Steams (1946) sug- 
gests that a center of volcanism was once active 
and formed the elongate ridge presently sur- 
mounted by Miihau, the island just west of 
Kauai. Macdonald et al. (I960) show many 
dikes in west Kauai which could be an exten- 
sion of a Niihau volcanic center. It should be 
possible to clarify the situation with additional 
gravity measurements, mainly on Niihau. How- 
ever, because of the angle between the two 
elongate Kauai gravity highs as presently 
mapped, it does not seem likely that they re- 
late to branches of a single volcanic system. 
Rather, it would appear that they point to an 
intergrowth of two distinct volcanoes. 
LOCAL GRAVITY FIELD 
Woollard (1951) offered the first complete 
interpretation of the gravity field of one of the 
Hawaiian Islands (Oahu). In this perceptive 
paper he described the probable source of the 
Waianae and Koolau gravity highs as the in- 
trusive complexes which mark their volcanic 
centers. This interpretation has been confirmed 
by recent studies of the gravity fields of active 
Hawaiian volcanoes (Kinoshita et ah, 1963). 
An additional mass excess may be provided by 
deeply ponded dense caldera fill. The juxtaposi- 
tion of intrusive complexes and caldera fill with 
density as great as 3, and of clinkery or scoria- 
ceous flow basalts with density of about 2.3, 
may produce the observed Bouguer anomaly. 
REGIONAL GRAVITY FIELD 
If Figure 2 is compared with the published 
Bouguer anomaly maps of Kilauea, Kohaia, 
Mauna Loa, Mauna Kea, Koolau, and Waianae, 
a striking difference is readily apparent. Kauai 
Bouguer values, both high and low, are 20-25 
mgal greater than are corresponding highs and 
lows on the volcanoes listed. 
Woollard and Strange (1962) offered im- 
portant data which bear on the gravity config- 
uration of the Pacific Basin. With an assump- 
tion of 0.4 density contrast between crust and 
mantle, Kauai’s gravity ( high as compared with 
the other volcanoes mentioned) could be ex- 
plained by up-warping and crustal thinning of 
4,000-5,000 ft. If the same density contrast is 
as great as 0.7, crustal thinning could be less 
than 3,000 ft. 
The Bouguer increase might be due also to 
a larger and/or more dense dike complex at 
