290 
PACIFIC SCIENCE, Vol. XX, July 1966 
using a susceptibility bridge, and for compara- 
tive remanence, using an astatic magnetometer. 
The samples ranged from tholeiite, collected 
from the Kilauea caldera walls, to alkalic ba- 
salt, collected from the area of recent eruption 
in the Puna district and from the 1919 and 1929 
Mauna Loa lava flows. Olivine nodule-rich lava 
samples were also collected from the 1801 
Hualalai lava flow. The susceptibilities ranged 
from 1.54 X 10“ 3 cgs units for tholeiite to 
3.62 X 10 -3 cgs units for samples of recent 
alkaline basalt. However, it should be noted 
that the susceptibilities of even neighboring 
samples of the same lava flow may vary by as 
much as — J— 1.0 X 10 -3 cgs units, depending on 
the absence or presence of local concentration 
of ferromagnetic minerals. Samples from rock 
quarries of massive fine-grained basalt, such as 
those collected in the vicinity of Kona airport, 
had variations of only — |— 0.2 cgs units. Olivine- 
rich samples of alkalic basalt from Hualalai 
Volcano yielded susceptibilities as low as 0.37 X 
10 -3 cgs units. This selection of surface 
samples, which certainly cannot be regarded as 
representative of the bulk of the lavas of the 
Hawaiian volcanoes, does give a reasonable as- 
semblage of representative susceptibilities. 
Decker (1963) obtained an excellent fit of 
measured and observed profiles across the walls 
and floor of the Kilauea caldera, using an 
average value of 1 X 10 -3 cgs units for sus- 
ceptibility of basalt and a natural remanent mag- 
netization of 10 X 10“ 3 cgs units. In the 
present study, the measured susceptibilities do 
not deviate by more than a factor of two from 
the averaged values of Decker. The observed 
remanence values are approximately the same. 
The value of susceptibility of 1.5 X 10“ 3 cgs 
units and a remanence of 11.0 X 10 -3 cgs 
units have been assumed in all the magnetic re- 
ductions and computations for the volcanoes of 
the Hawaiian Islands. 
By using depth estimation methods coupled 
with theoretical model studies, depth estimates 
and shape and size estimates were carried out 
for major magnetic anomalies. In order to sim- 
plify the mathematical computations, rectangu- 
lar shapes for the horizontal cross section of 
vents were adopted. 
A summary of all the analyses is shown in 
Table 2. The tops of the volcanic vent zones 
appear to lie within a zone extending from sea 
level to 4 km. The top surface of the postulated 
Ninole vent (Stearns and Macdonald, 1942), 
now buried beneath flows from Mauna Loa, 
appears to be located at a depth of 3.4 km below 
sea level. 
Another anomaly that is not represented by 
a surface feature is the Hilina volcanic vent. 
This feature is not reflected in the gravity 
anomalies (Fig. 15), yet it marks the center of 
a 400 -gamma peak-to-peak magnetic anomaly. 
In the geologic cross section by Stearns and 
Macdonald (Figs. 16 and 17), an upwarp of 
the Hilina volcanic series, as well as a system 
of faults, is shown to occur in the vicinity of 
the point of inflexion of the magnetic anomaly. 
Therefore, the Hilina magnetic anomaly (Figs. 
TABLE 2 
Analyses of the Total Force Magnetic Anomalies Over the Islands of Hawaii 
1* 
2* 
3* 
5* 
6* 
7* 
8* 
Kahuku pipe complex 
3.05 
14.5 by 09.5 
6.5 
— 3.40 
2.30 X 10-3 
400 
5 
Mauna Loa pipe complex 
4.30 
16.8 by 04.0 
2.7 
+ 1.60 
6.95 X IO - 3 
800 
20 
Hualalai pipe complex 
3.05 
8.8 by 04.9 
1.3 
+ 1.75 
6.95 X 10-3 
800 
15 
Kohala pipe complex 
3.05 
8.8 by 11.2 
5.7 
-2.65 
14.00 X 10-3 
800 
10 
Hilina pipe complex 
3.05 
9-6 by 05.6 
4.0 
—0.95 
11.30 X 10-3 
400 
12 
Mauna Kea pipe complex 
4.30 
12.0 by 06.0 
1.9 
+ 2.70 
13-80 X 10-3 
1500 
8 
1* Name of feature. 
2 * Elevation of flight level above sea level in kilometers. 
3* Cross sectional size of anomalous body in kilometers from the total magnetic intensity map. 
4 * Depth estimates to top of anomalous body in kilometers (Vacquier method). 
5* Top of anomalous body with respect to sea level in kilometers. 
6* Magnetization contrast of anomalous body with surrounding rock in cgs units (Vacquier method). 
7 * Maximum amplitude of anomaly in gammas peak-to-peak. 
8* Length of anomalous body in kilometers from theoretical models. 
