29 2 
PACIFIC SCIENCE, Vol. XX, July 1966 
Fig. 17 . Implied geological cross-section across Kilauea Volcano, island of Hawaii, with magnetic and 
gravity profiles along line A- A' (see Figs. 16 and 18 ). 
methods. However, the writers believe that, 
because the total force magnetic dipole anoma- 
lies are distinct and can be reasonably approxi- 
mated by Vacquier models, the G indices for 
the magnetic anomalies of Hawaii cannot be in 
error by more than 0.5 km. 
The apparent susceptibility contrast between 
the rocks of the volcanic vent complexes, cal- 
culated by using Vacquier’ s relationships, varies 
between 2.3 X 10“ 3 cgs units for the Ninole 
vent and 14.0 X 10 “ 3 cgs units for the Kohala 
vent. 
It is obvious from a study of Figure 16 and 
the above data that the horizontal dimensions 
of all the vent complexes are in excess of their 
geologic expression. This difference might well 
reflect the presence of shallow magma chambers 
as postulated by Eaton (1962), or represent a 
spreading of the vent zone at depth, as sug- 
gested by analyses of the gravity anomalies as- 
sociated with vents. Judging from the analyses 
of the vertical dimensions of the volcanic vent 
zones, the intrusive rock complex in the vents 
on the island of Hawaii extend upward from a 
depth of 19 km below present sea level (some 
4-5 km beneath the present level of the 
Mohorovicic discontinuity) to near the present 
surface. It is important to note though, that the 
bottom level of a 20-km-long vent zone may be 
varied by as much as 3 km without influencing 
the total anomaly profile by more than 5-20 
gammas. Similarly, the bottom of the vent zone 
may be raised or lowered by several kilometers 
by altering slightly the general susceptibility con- 
trast or natural remanent magnetization. 
Inasmuch as the top of the Ninole vent com- 
plex lies at the deepest level, it could represent 
the oldest vent, but this is by no means certain. 
Certainly one would not interpret the fact that 
the top of the vent complex associated with 
Mauna Kea Volcano stands higher than that 
associated with Mauna Loa as indicating that it 
is the younger of the two. 
MAGNETIC EFFECT OF TERRAIN ON THE 
island of Hawaii: As stated previously, the 
flight elevations for taking the profiles in Ha- 
waii were chosen so as to minimize the effect 
of terrain. All of the magnetic profiles used in 
